SMART ARM-based Microcontrollers
AT03243: SAM D/R Analog to Digital Converter
(ADC) Driver
APPLICATION NOTE
Introduction
®
®
This driver for Atmel | SMART ARM -based microcontrollers provides an
interface for the configuration and management of the device's Analog-toDigital Converter functionality, for the conversion of analog voltages into a
corresponding digital form. The following driver Application Programming
Interface (API) modes are covered by this manual:
•
Polled APIs
•
Callback APIs
The following peripheral is used by this module:
•
ADC (Analog-to-Digital Converter)
The following devices can use this module:
•
Atmel | SMART SAM D20/D21
•
Atmel | SMART SAM R21
•
Atmel | SMART SAM D09/D10/D11
•
Atmel | SMART SAM DA1
The outline of this documentation is as follows:
•
Prerequisites
•
Module Overview
•
Special Considerations
•
Extra Information
•
Examples
•
API Overview
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Table of Contents
Introduction......................................................................................................................1
1. Software License....................................................................................................... 4
2. Prerequisites..............................................................................................................5
3. Module Overview....................................................................................................... 6
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
3.7.
3.8.
3.9.
3.10.
Sample Clock Prescaler............................................................................................................... 6
ADC Resolution............................................................................................................................6
Conversion Modes........................................................................................................................7
Differential and Single-ended Conversion.................................................................................... 7
Sample Time................................................................................................................................ 7
Averaging..................................................................................................................................... 7
Offset and Gain Correction...........................................................................................................8
Pin Scan....................................................................................................................................... 9
Window Monitor............................................................................................................................9
Events...........................................................................................................................................9
4. Special Considerations............................................................................................ 10
5. Extra Information......................................................................................................11
6. Examples................................................................................................................. 12
7. API Overview........................................................................................................... 13
7.1.
7.2.
7.3.
7.4.
7.5.
Variable and Type Definitions..................................................................................................... 13
7.1.1.
Type adc_callback_t.................................................................................................... 13
Structure Definitions................................................................................................................... 13
7.2.1.
Struct adc_config......................................................................................................... 13
7.2.2.
Struct adc_correction_config....................................................................................... 14
7.2.3.
Struct adc_events........................................................................................................ 15
7.2.4.
Struct adc_module.......................................................................................................15
7.2.5.
Struct adc_pin_scan_config.........................................................................................15
7.2.6.
Struct adc_window_config........................................................................................... 15
Macro Definitions........................................................................................................................16
7.3.1.
Module Status Flags.................................................................................................... 16
Function Definitions....................................................................................................................16
7.4.1.
Driver Initialization and Configuration.......................................................................... 16
7.4.2.
Status Management.....................................................................................................18
7.4.3.
Enable, Disable, and Reset ADC Module, Start Conversion and Read Result........... 19
7.4.4.
Runtime Changes of ADC Module...............................................................................21
7.4.5.
Enable and Disable Interrupts..................................................................................... 22
7.4.6.
Callback Management................................................................................................. 23
7.4.7.
Job Management......................................................................................................... 25
7.4.8.
ADC Gain and Pin Scan Mode.................................................................................... 26
Enumeration Definitions............................................................................................................. 27
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7.5.1.
Enum adc_accumulate_samples.................................................................................27
7.5.2.
7.5.3.
7.5.4.
7.5.5.
7.5.6.
7.5.7.
7.5.8.
7.5.9.
7.5.10.
7.5.11.
7.5.12.
7.5.13.
7.5.14.
Enum adc_callback......................................................................................................28
Enum adc_clock_prescaler..........................................................................................28
Enum adc_divide_result.............................................................................................. 29
Enum adc_event_action.............................................................................................. 29
Enum adc_gain_factor.................................................................................................29
Enum adc_interrupt_flag..............................................................................................30
Enum adc_job_type..................................................................................................... 30
Enum adc_negative_input........................................................................................... 30
Enum adc_oversampling_and_decimation..................................................................31
Enum adc_positive_input.............................................................................................31
Enum adc_reference................................................................................................... 32
Enum adc_resolution................................................................................................... 32
Enum adc_window_mode............................................................................................33
8. Extra Information for ADC Driver............................................................................. 34
8.1.
8.2.
8.3.
8.4.
Acronyms....................................................................................................................................34
Dependencies.............................................................................................................................34
Errata..........................................................................................................................................34
Module History............................................................................................................................34
9. Examples for ADC Driver.........................................................................................35
9.1.
9.2.
9.3.
Quick Start Guide for ADC - Basic............................................................................................. 35
9.1.1.
Setup........................................................................................................................... 35
9.1.2.
Use Case..................................................................................................................... 36
Quick Start Guide for ADC - Callback........................................................................................ 37
9.2.1.
Setup........................................................................................................................... 37
9.2.2.
Use Case..................................................................................................................... 40
Quick Start Guide for Using DMA with ADC/DAC...................................................................... 40
9.3.1.
Setup........................................................................................................................... 41
9.3.2.
Use Case..................................................................................................................... 46
10. Document Revision History..................................................................................... 48
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1.
Software License
Redistribution and use in source and binary forms, with or without modification, are permitted provided
that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this list of conditions and the
following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other materials provided with the distribution.
3. The name of Atmel may not be used to endorse or promote products derived from this software without
specific prior written permission.
4. This software may only be redistributed and used in connection with an Atmel microcontroller product.
THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE EXPRESSLY AND SPECIFICALLY
DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
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2.
Prerequisites
There are no prerequisites for this module.
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3.
Module Overview
This driver provides an interface for the Analog-to-Digital conversion functions on the device, to convert
analog voltages to a corresponding digital value. The ADC has up to 12-bit resolution, and is capable of
converting up to 500K samples per second (KSPS).
The ADC has a compare function for accurate monitoring of user defined thresholds with minimum
software intervention required. The ADC may be configured for 8-, 10-, or 12-bit result, reducing the
conversion time. ADC conversion results are provided left or right adjusted which eases calculation when
the result is represented as a signed integer.
The input selection is flexible, and both single-ended and differential measurements can be made. For
differential measurements, an optional gain stage is available to increase the dynamic range. In addition,
several internal signal inputs are available. The ADC can provide both signed and unsigned results.
The ADC measurements can either be started by application software or an incoming event from another
peripheral in the device, and both internal and external reference voltages can be selected.
Note: Internal references will be enabled by the driver, but not disabled. Any reference not used by the
application should be disabled by the application.
A simplified block diagram of the ADC can be seen in Figure 3-1 Module Overview on page 6.
Figure 3-1. Module Overview
PRESCALER
Positive input
Negative input
ADC
Post processing
RESULT
Reference
3.1.
Sample Clock Prescaler
The ADC features a prescaler, which enables conversion at lower clock rates than the input Generic
Clock to the ADC module. This feature can be used to lower the synchronization time of the digital
interface to the ADC module via a high speed Generic Clock frequency, while still allowing the ADC
sampling rate to be reduced.
3.2.
ADC Resolution
The ADC supports full 8-, 10-, or 12-bit resolution. Hardware oversampling and decimation can be used
to increase the effective resolution at the expense of throughput. Using oversampling and decimation
mode the ADC resolution is increased from 12-bit to an effective 13-, 14-, 15-, or 16-bit. In these modes
the conversion rate is reduced, as a greater number of samples is used to achieve the increased
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resolution. The available resolutions and effective conversion rate is listed in Table 3-1 Effective ADC
Conversion Speed Using Oversampling on page 7.
Table 3-1. Effective ADC Conversion Speed Using Oversampling
3.3.
Resolution
Effective conversion rate
13-bit
Conversion rate divided by 4
14-bit
Conversion rate divided by 16
15-bit
Conversion rate divided by 64
16-bit
Conversion rate divided by 256
Conversion Modes
ADC conversions can be software triggered on demand by the user application, if continuous sampling is
not required. It is also possible to configure the ADC in free running mode, where new conversions are
started as soon as the previous conversion is completed, or configure the ADC to scan across a number
of input pins (see Pin Scan).
3.4.
Differential and Single-ended Conversion
The ADC has two conversion modes; differential and single-ended. When measuring signals where the
positive input pin is always at a higher voltage than the negative input pin, the single-ended conversion
mode should be used in order to achieve a full 12-bit output resolution.
If however the positive input pin voltage may drop below the negative input pin the signed differential
mode should be used.
3.5.
Sample Time
The sample time for each ADC conversion is configurable as a number of half prescaled ADC clock
cycles (depending on the prescaler value), allowing the user application to achieve faster or slower
sampling depending on the source impedance of the ADC input channels. For applications with high
impedance inputs the sample time can be increased to give the ADC an adequate time to sample and
convert the input channel.
The resulting sampling time is given by the following equation:
������
������� = ������_�����ℎ + 1 ×
2
3.6.
Averaging
The ADC can be configured to trade conversion speed for accuracy by averaging multiple samples in
hardware. This feature is suitable when operating in noisy conditions.
You can specify any number of samples to accumulate (up to 1024) and the divide ratio to use (up to
divide by 128). To modify these settings the ADC_RESOLUTION_CUSTOM needs to be set as the
resolution. When this is set the number of samples to accumulate and the division ratio can be set by the
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configuration struct members adc_config::accumulate_samples and adc_config::divide_result. When
using this mode the ADC result register will be set to be 16-bit wide to accommodate the larger result
sizes produced by the accumulator.
The effective ADC conversion rate will be reduced by a factor of the number of accumulated samples;
however, the effective resolution will be increased according to Table 3-2 Effective ADC Resolution From
Various Hardware Averaging Modes on page 8.
Table 3-2. Effective ADC Resolution From Various Hardware Averaging Modes
3.7.
Number of samples
Final result
1
12-bit
2
13-bit
4
14-bit
8
15-bit
16
16-bit
32
16-bit
64
16-bit
128
16-bit
256
16-bit
512
16-bit
1024
16-bit
Offset and Gain Correction
Inherent gain and offset errors affect the absolute accuracy of the ADC.
The offset error is defined as the deviation of the ADC's actual transfer function from ideal straight line at
zero input voltage.
The gain error is defined as the deviation of the last output step's midpoint from the ideal straight line,
after compensating for offset error.
The offset correction value is subtracted from the converted data before the result is ready. The gain
correction value is multiplied with the offset corrected value.
The equation for both offset and gain error compensation is shown below:
��������� = ��������� + ���������� × ��������
When enabled, a given set of offset and gain correction values can be applied to the sampled data in
hardware, giving a corrected stream of sample data to the user application at the cost of an increased
sample latency.
In single conversion, a latency of 13 ADC Generic Clock cycles is added for the final sample result
availability. As the correction time is always less than the propagation delay, in free running mode this
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latency appears only during the first conversion. After the first conversion is complete, future conversion
results are available at the defined sampling rate.
3.8.
Pin Scan
In pin scan mode, the first ADC conversion will begin from the configured positive channel, plus the
requested starting offset. When the first conversion is completed, the next conversion will start at the next
positive input channel and so on, until all requested pins to scan have been sampled and converted. SAM
L21/L22 has automatic sequences feature instead of pin scan mode. In automatic sequence mode, all of
32 positives inputs can be included in a sequence. The sequence starts from the lowest input, and go to
the next enabled input automatically.
Pin scanning gives a simple mechanism to sample a large number of physical input channel samples,
using a single physical ADC channel.
3.9.
Window Monitor
The ADC module window monitor function can be used to automatically compare the conversion result
against a preconfigured pair of upper and lower threshold values.
The threshold values are evaluated differently, depending on whether differential or single-ended mode is
selected. In differential mode, the upper and lower thresholds are evaluated as signed values for the
comparison, while in single-ended mode the comparisons are made as a set of unsigned values.
The significant bits of the lower window monitor threshold and upper window monitor threshold values are
user-configurable, and follow the overall ADC sampling bit precision set when the ADC is configured by
the user application. For example, only the eight lower bits of the window threshold values will be
compared to the sampled data whilst the ADC is configured in 8-bit mode. In addition, if using differential
mode, the 8th bit will be considered as the sign bit even if bit 9 is zero.
3.10.
Events
Event generation and event actions are configurable in the ADC.
The ADC has two actions that can be triggered upon event reception:
•
Start conversion
•
Flush pipeline and start conversion
The ADC can generate two events:
•
Window monitor
•
Result ready
If the event actions are enabled in the configuration, any incoming event will trigger the action.
If the window monitor event is enabled, an event will be generated when the configured window condition
is detected.
If the result ready event is enabled, an event will be generated when a conversion is completed.
Note: The connection of events between modules requires the use of the SAM Event System Driver
(EVENTS) to route output event of one module to the input event of another. For more information on
event routing, refer to the event driver documentation.
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4.
Special Considerations
An integrated analog temperature sensor is available for use with the ADC. The bandgap voltage, as well
as the scaled I/O and core voltages can also be measured by the ADC. For internal ADC inputs, the
internal source(s) may need to be manually enabled by the user application before they can be
measured.
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5.
Extra Information
For extra information, see Extra Information for ADC Driver. This includes:
•
Acronyms
•
Dependencies
•
Errata
•
Module History
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6.
Examples
For a list of examples related to this driver, see Examples for ADC Driver.
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7.
API Overview
7.1.
Variable and Type Definitions
7.1.1.
Type adc_callback_t
typedef void(* adc_callback_t )(struct adc_module *const module)
Type of the callback functions.
7.2.
Structure Definitions
7.2.1.
Struct adc_config
Configuration structure for an ADC instance. This structure should be initialized by the
adc_get_config_defaults() function before being modified by the user application.
Table 7-1. Members
Type
Name
Description
enum
adc_accumulate_samples
accumulate_samples
Number of ADC samples to accumulate
when using the
ADC_RESOLUTION_CUSTOM mode.
Note: if the result width increases, result
resolution will be changed accordingly.
enum adc_clock_prescaler
clock_prescaler
Clock prescaler
enum gclk_generator
clock_source
GCLK generator used to clock the
peripheral
struct
adc_correction_config
correction
Gain and offset correction configuration
structure
bool
differential_mode
Enables differential mode if true. if false,
ADC will run in singled-ended mode.
enum adc_divide_result
divide_result
Division ration when using the
ADC_RESOLUTION_CUSTOM mode
enum adc_event_action
event_action
Event action to take on incoming event
bool
freerunning
Enables free running mode if true
enum adc_gain_factor
gain_factor
Gain factor
bool
left_adjust
Left adjusted result
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7.2.2.
Type
Name
Description
enum adc_negative_input
negative_input
Negative MUX input. For singled-ended
conversion mode, the negative input
must be connected to ground. This
ground could be the internal GND,
IOGND or an external ground
connected to a pin.
struct adc_pin_scan_config pin_scan
Pin scan configuration structure
enum adc_positive_input
positive_input
Positive Multiplexer (MUX) input
enum adc_reference
reference
Voltage reference
bool
reference_compensation_enable Enables reference buffer offset
compensation if true. This will increase
the accuracy of the gain stage, but
decreases the input impedance;
therefore the startup time of the
reference must be increased.
enum adc_resolution
resolution
Result resolution
bool
run_in_standby
Enables ADC in standby sleep mode if
true
uint8_t
sample_length
This value (0-63) control the ADC
sampling time in number of half ADC
prescaled clock cycles (depends of
ADC_PRESCALER value), thus
controlling the ADC input impedance.
Sampling time is set according to the
formula: Sample time = (sample_length
+1) * (ADCclk / 2).
struct adc_window_config
window
Window monitor configuration structure
Struct adc_correction_config
Gain and offset correction configuration structure. Part of the adc_config struct and will be initialized by
adc_get_config_defaults.
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Table 7-2. Members
7.2.3.
Type
Name
Description
bool
correction_enable Enables correction for gain and offset based on values of gain_correction
and offset_correction if set to true
uint16_t gain_correction
This value defines how the ADC conversion result is compensated for gain
error before written to the result register. This is a fractional value, 1-bit
integer plus an 11-bit fraction, therefore 1/2 <= gain_correction < 2. Valid
gain_correction values ranges from 0b010000000000 to
0b111111111111.
int16_t
This value defines how the ADC conversion result is compensated for
offset error before written to the result register. This is a 12-bit value in
two's complement format.
offset_correction
Struct adc_events
Event flags for the ADC module. This is used to enable and disable events via adc_enable_events() and
adc_disable_events().
Table 7-3. Members
7.2.4.
Type
Name
Description
bool
generate_event_on_conversion_done
Enable event generation on conversion done
bool
generate_event_on_window_monitor
Enable event generation on window monitor
Struct adc_module
ADC software instance structure, used to retain software state information of an associated hardware
module instance.
Note: The fields of this structure should not be altered by the user application; they are reserved for
module-internal use only.
7.2.5.
Struct adc_pin_scan_config
Pin scan configuration structure. Part of the adc_config struct and will be initialized by
adc_get_config_defaults.
Table 7-4. Members
Type
Name
Description
uint8_t inputs_to_scan
Number of input pins to scan in pin scan mode. A value below two will
disable pin scan mode.
uint8_t offset_start_scan Offset (relative to selected positive input) of the first input pin to be used in
pin scan mode
7.2.6.
Struct adc_window_config
Window monitor configuration structure.
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Table 7-5. Members
Type
Name
Description
int32_t
window_lower_value
Lower window value
enum adc_window_mode
window_mode
Selected window mode
int32_t
window_upper_value
Upper window value
7.3.
Macro Definitions
7.3.1.
Module Status Flags
ADC status flags, returned by adc_get_status() and cleared by adc_clear_status().
7.3.1.1.
Macro ADC_STATUS_RESULT_READY
#define ADC_STATUS_RESULT_READY
ADC result ready.
7.3.1.2.
Macro ADC_STATUS_WINDOW
#define ADC_STATUS_WINDOW
Window monitor match.
7.3.1.3.
Macro ADC_STATUS_OVERRUN
#define ADC_STATUS_OVERRUN
ADC result overwritten before read.
7.4.
Function Definitions
7.4.1.
Driver Initialization and Configuration
7.4.1.1.
Function adc_init()
Initializes the ADC.
enum status_code adc_init(
struct adc_module *const module_inst,
Adc * hw,
struct adc_config * config)
Initializes the ADC device struct and the hardware module based on the given configuration struct values.
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Table 7-6. Parameters
Data direction
Parameter name
Description
[out]
module_inst
Pointer to the ADC software instance struct
[in]
hw
Pointer to the ADC module instance
[in]
config
Pointer to the configuration struct
Returns
Status of the initialization procedure.
Table 7-7. Return Values
7.4.1.2.
Return value
Description
STATUS_OK
The initialization was successful
STATUS_ERR_INVALID_ARG
Invalid argument(s) were provided
STATUS_BUSY
The module is busy with a reset operation
STATUS_ERR_DENIED
The module is enabled
Function adc_get_config_defaults()
Initializes an ADC configuration structure to defaults.
void adc_get_config_defaults(
struct adc_config *const config)
Initializes a given ADC configuration struct to a set of known default values. This function should be called
on any new instance of the configuration struct before being modified by the user application.
The default configuration is as follows:
•
GCLK generator 0 (GCLK main) clock source
•
1V from internal bandgap reference
•
Div 4 clock prescaler
•
12-bit resolution
•
Window monitor disabled
•
No gain
•
Positive input on ADC PIN 0
•
Negative input on ADC PIN 1
•
Averaging disabled
•
Oversampling disabled
•
Right adjust data
•
Single-ended mode
•
Free running disabled
•
All events (input and generation) disabled
•
Sleep operation disabled
•
No reference compensation
•
No gain/offset correction
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•
•
No added sampling time
Pin scan mode disabled
Table 7-8. Parameters
Data direction
Parameter name
Description
[out]
config
Pointer to configuration struct to initialize to default values
7.4.2.
Status Management
7.4.2.1.
Function adc_get_status()
Retrieves the current module status.
uint32_t adc_get_status(
struct adc_module *const module_inst)
Retrieves the status of the module, giving overall state information.
Table 7-9. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Returns
Bitmask of ADC_STATUS_* flags.
Table 7-10. Return Values
7.4.2.2.
Return value
Description
ADC_STATUS_RESULT_READY
ADC result is ready to be read
ADC_STATUS_WINDOW
ADC has detected a value inside the set window range
ADC_STATUS_OVERRUN
ADC result has overrun
Function adc_clear_status()
Clears a module status flag.
void adc_clear_status(
struct adc_module *const module_inst,
const uint32_t status_flags)
Clears the given status flag of the module.
Table 7-11. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
status_flags
Bitmask of ADC_STATUS_* flags to clear
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7.4.3.
Enable, Disable, and Reset ADC Module, Start Conversion and Read Result
7.4.3.1.
Function adc_enable()
Enables the ADC module.
enum status_code adc_enable(
struct adc_module *const module_inst)
Enables an ADC module that has previously been configured. If any internal reference is selected it will
be enabled.
Table 7-12. Parameters
7.4.3.2.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Function adc_disable()
Disables the ADC module.
enum status_code adc_disable(
struct adc_module *const module_inst)
Disables an ADC module that was previously enabled.
Table 7-13. Parameters
7.4.3.3.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Function adc_reset()
Resets the ADC module.
enum status_code adc_reset(
struct adc_module *const module_inst)
Resets an ADC module, clearing all module state, and registers to their default values.
Table 7-14. Parameters
7.4.3.4.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Function adc_enable_events()
Enables an ADC event input or output.
void adc_enable_events(
struct adc_module *const module_inst,
struct adc_events *const events)
Enables one or more input or output events to or from the ADC module. See Struct adc_events for a list
of events this module supports.
Note: Events cannot be altered while the module is enabled.
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Table 7-15. Parameters
7.4.3.5.
Data direction
Parameter name
Description
[in]
module_inst
Software instance for the ADC peripheral
[in]
events
Struct containing flags of events to enable
Function adc_disable_events()
Disables an ADC event input or output.
void adc_disable_events(
struct adc_module *const module_inst,
struct adc_events *const events)
Disables one or more input or output events to or from the ADC module. See Struct adc_events for a list
of events this module supports.
Note: Events cannot be altered while the module is enabled.
Table 7-16. Parameters
7.4.3.6.
Data direction
Parameter name
Description
[in]
module_inst
Software instance for the ADC peripheral
[in]
events
Struct containing flags of events to disable
Function adc_start_conversion()
Starts an ADC conversion.
void adc_start_conversion(
struct adc_module *const module_inst)
Starts a new ADC conversion.
Table 7-17. Parameters
7.4.3.7.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Function adc_read()
Reads the ADC result.
enum status_code adc_read(
struct adc_module *const module_inst,
uint16_t * result)
Reads the result from an ADC conversion that was previously started.
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Table 7-18. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[out]
result
Pointer to store the result value in
Returns
Status of the ADC read request.
Table 7-19. Return Values
Return value
Description
STATUS_OK
The result was retrieved successfully
STATUS_BUSY
A conversion result was not ready
STATUS_ERR_OVERFLOW The result register has been overwritten by the ADC module before the
result was read by the software
7.4.4.
Runtime Changes of ADC Module
7.4.4.1.
Function adc_flush()
Flushes the ADC pipeline.
void adc_flush(
struct adc_module *const module_inst)
Flushes the pipeline and restarts the ADC clock on the next peripheral clock edge. All conversions in
progress will be lost. When flush is complete, the module will resume where it left off.
Table 7-20. Parameters
7.4.4.2.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
Function adc_set_window_mode()
Sets the ADC window mode.
void adc_set_window_mode(
struct adc_module *const module_inst,
const enum adc_window_mode window_mode,
const int16_t window_lower_value,
const int16_t window_upper_value)
Sets the ADC window mode to a given mode and value range.
Table 7-21. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
window_mode
Window monitor mode to set
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7.4.4.3.
Data direction
Parameter name
Description
[in]
window_lower_value
Lower window monitor threshold value
[in]
window_upper_value
Upper window monitor threshold value
Function adc_set_positive_input()
Sets positive ADC input pin.
void adc_set_positive_input(
struct adc_module *const module_inst,
const enum adc_positive_input positive_input)
Sets the positive ADC input pin selection.
Table 7-22. Parameters
7.4.4.4.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
positive_input
Positive input pin
Function adc_set_negative_input()
Sets negative ADC input pin for differential mode.
void adc_set_negative_input(
struct adc_module *const module_inst,
const enum adc_negative_input negative_input)
Sets the negative ADC input pin, when the ADC is configured in differential mode.
Table 7-23. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
negative_input
Negative input pin
7.4.5.
Enable and Disable Interrupts
7.4.5.1.
Function adc_enable_interrupt()
Enable interrupt.
void adc_enable_interrupt(
struct adc_module *const module_inst,
enum adc_interrupt_flag interrupt)
Enable the given interrupt request from the ADC module.
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Table 7-24. Parameters
7.4.5.2.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
interrupt
Interrupt to enable
Function adc_disable_interrupt()
Disable interrupt.
void adc_disable_interrupt(
struct adc_module *const module_inst,
enum adc_interrupt_flag interrupt)
Disable the given interrupt request from the ADC module.
Table 7-25. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
interrupt
Interrupt to disable
7.4.6.
Callback Management
7.4.6.1.
Function adc_register_callback()
Registers a callback.
void adc_register_callback(
struct adc_module *const module,
adc_callback_t callback_func,
enum adc_callback callback_type)
Registers a callback function which is implemented by the user.
Note: The callback must be enabled by for the interrupt handler to call it when the condition for the
callback is met.
Table 7-26. Parameters
7.4.6.2.
Data direction
Parameter name
Description
[in]
module
Pointer to ADC software instance struct
[in]
callback_func
Pointer to callback function
[in]
callback_type
Callback type given by an enum
Function adc_unregister_callback()
Unregisters a callback.
void adc_unregister_callback(
struct adc_module * module,
enum adc_callback callback_type)
Unregisters a callback function which is implemented by the user.
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Table 7-27. Parameters
7.4.6.3.
Data direction
Parameter name
Description
[in]
module
Pointer to ADC software instance struct
[in]
callback_type
Callback type given by an enum
Function adc_enable_callback()
Enables callback.
void adc_enable_callback(
struct adc_module *const module,
enum adc_callback callback_type)
Enables the callback function registered by adc_register_callback. The callback function will be called
from the interrupt handler when the conditions for the callback type are met.
Table 7-28. Parameters
Data direction
Parameter name
Description
[in]
module
Pointer to ADC software instance struct
[in]
callback_type
Callback type given by an enum
Returns
Status of the operation.
Table 7-29. Return Values
7.4.6.4.
Return value
Description
STATUS_OK
If operation was completed
STATUS_ERR_INVALID
If operation was not completed, due to invalid callback_type
Function adc_disable_callback()
Disables callback.
void adc_disable_callback(
struct adc_module *const module,
enum adc_callback callback_type)
Disables the callback function registered by the adc_register_callback.
Table 7-30. Parameters
Data direction
Parameter name
Description
[in]
module
Pointer to ADC software instance struct
[in]
callback_type
Callback type given by an enum
Returns
Status of the operation.
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Table 7-31. Return Values
Return value
Description
STATUS_OK
If operation was completed
STATUS_ERR_INVALID
If operation was not completed, due to invalid callback_type
7.4.7.
Job Management
7.4.7.1.
Function adc_read_buffer_job()
Read multiple samples from ADC.
enum status_code adc_read_buffer_job(
struct adc_module *const module_inst,
uint16_t * buffer,
uint16_t samples)
Read samples samples from the ADC into the buffer buffer. If there is no hardware trigger defined
(event action) the driver will retrigger the ADC conversion whenever a conversion is complete until
samples samples has been acquired. To avoid jitter in the sampling frequency using an event trigger is
advised.
Table 7-32. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
samples
Number of samples to acquire
[out]
buffer
Buffer to store the ADC samples
Returns
Status of the job start.
Table 7-33. Return Values
7.4.7.2.
Return value
Description
STATUS_OK
The conversion job was started successfully and is in progress
STATUS_BUSY
The ADC is already busy with another job
Function adc_get_job_status()
Gets the status of a job.
enum status_code adc_get_job_status(
struct adc_module * module_inst,
enum adc_job_type type)
Gets the status of an ongoing or the last job.
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Table 7-34. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
type
Type of job to get status
Returns
Status of the job.
7.4.7.3.
Function adc_abort_job()
Aborts an ongoing job.
void adc_abort_job(
struct adc_module * module_inst,
enum adc_job_type type)
Aborts an ongoing job.
Table 7-35. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
type
Type of job to abort
7.4.8.
ADC Gain and Pin Scan Mode
7.4.8.1.
Function adc_set_gain()
Sets ADC gain factor.
void adc_set_gain(
struct adc_module *const module_inst,
const enum adc_gain_factor gain_factor)
Sets the ADC gain factor to a specified gain setting.
Table 7-36. Parameters
7.4.8.2.
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
gain_factor
Gain factor value to set
Function adc_set_pin_scan_mode()
Sets the ADC pin scan mode.
enum status_code adc_set_pin_scan_mode(
struct adc_module *const module_inst,
uint8_t inputs_to_scan,
const uint8_t start_offset)
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Configures the pin scan mode of the ADC module. In pin scan mode, the first conversion will start at the
configured positive input + start_offset. When a conversion is done, a conversion will start on the next
input, until inputs_to_scan number of conversions are made.
Table 7-37. Parameters
Data direction Parameter name Description
[in]
module_inst
Pointer to the ADC software instance struct
[in]
inputs_to_scan
Number of input pins to perform a conversion on (must be two or
more)
[in]
start_offset
Offset of first pin to scan (relative to configured positive input)
Returns
Status of the pin scan configuration set request.
Table 7-38. Return Values
7.4.8.3.
Return value
Description
STATUS_OK
Pin scan mode has been set successfully
STATUS_ERR_INVALID_ARG
Number of input pins to scan or offset has an invalid value
Function adc_disable_pin_scan_mode()
Disables pin scan mode.
void adc_disable_pin_scan_mode(
struct adc_module *const module_inst)
Disables pin scan mode. The next conversion will be made on only one pin (the configured positive input
pin).
Table 7-39. Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the ADC software instance struct
7.5.
Enumeration Definitions
7.5.1.
Enum adc_accumulate_samples
Enum for the possible numbers of ADC samples to accumulate. This setting is only used when the
ADC_RESOLUTION_CUSTOM resolution setting is used.
Table 7-40. Members
Enum value
Description
ADC_ACCUMULATE_DISABLE
No averaging
ADC_ACCUMULATE_SAMPLES_2
Average 2 samples
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7.5.2.
Enum value
Description
ADC_ACCUMULATE_SAMPLES_4
Average 4 samples
ADC_ACCUMULATE_SAMPLES_8
Average 8 samples
ADC_ACCUMULATE_SAMPLES_16
Average 16 samples
ADC_ACCUMULATE_SAMPLES_32
Average 32 samples
ADC_ACCUMULATE_SAMPLES_64
Average 64 samples
ADC_ACCUMULATE_SAMPLES_128
Average 128 samples
ADC_ACCUMULATE_SAMPLES_256
Average 256 samples
ADC_ACCUMULATE_SAMPLES_512
Average 512 samples
ADC_ACCUMULATE_SAMPLES_1024
Average 1024 samples
Enum adc_callback
Callback types for ADC callback driver.
Table 7-41. Members
7.5.3.
Enum value
Description
ADC_CALLBACK_READ_BUFFER
Callback for buffer received
ADC_CALLBACK_WINDOW
Callback when window is hit
ADC_CALLBACK_ERROR
Callback for error
Enum adc_clock_prescaler
Enum for the possible clock prescaler values for the ADC.
Table 7-42. Members
Enum value
Description
ADC_CLOCK_PRESCALER_DIV4
ADC clock division factor 4
ADC_CLOCK_PRESCALER_DIV8
ADC clock division factor 8
ADC_CLOCK_PRESCALER_DIV16
ADC clock division factor 16
ADC_CLOCK_PRESCALER_DIV32
ADC clock division factor 32
ADC_CLOCK_PRESCALER_DIV64
ADC clock division factor 64
ADC_CLOCK_PRESCALER_DIV128
ADC clock division factor 128
ADC_CLOCK_PRESCALER_DIV256
ADC clock division factor 256
ADC_CLOCK_PRESCALER_DIV512
ADC clock division factor 512
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7.5.4.
Enum adc_divide_result
Enum for the possible division factors to use when accumulating multiple samples. To keep the same
resolution for the averaged result and the actual input value, the division factor must be equal to the
number of samples accumulated. This setting is only used when the ADC_RESOLUTION_CUSTOM
resolution setting is used.
Table 7-43. Members
7.5.5.
Enum value
Description
ADC_DIVIDE_RESULT_DISABLE
Don't divide result register after accumulation
ADC_DIVIDE_RESULT_2
Divide result register by 2 after accumulation
ADC_DIVIDE_RESULT_4
Divide result register by 4 after accumulation
ADC_DIVIDE_RESULT_8
Divide result register by 8 after accumulation
ADC_DIVIDE_RESULT_16
Divide result register by 16 after accumulation
ADC_DIVIDE_RESULT_32
Divide result register by 32 after accumulation
ADC_DIVIDE_RESULT_64
Divide result register by 64 after accumulation
ADC_DIVIDE_RESULT_128
Divide result register by 128 after accumulation
Enum adc_event_action
Enum for the possible actions to take on an incoming event.
Table 7-44. Members
7.5.6.
Enum value
Description
ADC_EVENT_ACTION_DISABLED
Event action disabled
ADC_EVENT_ACTION_FLUSH_START_CONV
Flush ADC and start conversion
ADC_EVENT_ACTION_START_CONV
Start conversion
Enum adc_gain_factor
Enum for the possible gain factor values for the ADC.
Table 7-45. Members
Enum value
Description
ADC_GAIN_FACTOR_1X
1x gain
ADC_GAIN_FACTOR_2X
2x gain
ADC_GAIN_FACTOR_4X
4x gain
ADC_GAIN_FACTOR_8X
8x gain
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7.5.7.
Enum value
Description
ADC_GAIN_FACTOR_16X
16x gain
ADC_GAIN_FACTOR_DIV2
1/2x gain
Enum adc_interrupt_flag
Enum for the possible ADC interrupt flags.
Table 7-46. Members
7.5.8.
Enum value
Description
ADC_INTERRUPT_RESULT_READY
ADC result ready
ADC_INTERRUPT_WINDOW
Window monitor match
ADC_INTERRUPT_OVERRUN
ADC result overwritten before read
Enum adc_job_type
Enum for the possible types of ADC asynchronous jobs that may be issued to the driver.
Table 7-47. Members
7.5.9.
Enum value
Description
ADC_JOB_READ_BUFFER
Asynchronous ADC read into a user provided buffer
Enum adc_negative_input
Enum for the possible negative Multiplexer(MUX) input selections for the ADC.
Table 7-48. Members
Enum value
Description
ADC_NEGATIVE_INPUT_PIN0
ADC0 pin
ADC_NEGATIVE_INPUT_PIN1
ADC1 pin
ADC_NEGATIVE_INPUT_PIN2
ADC2 pin
ADC_NEGATIVE_INPUT_PIN3
ADC3 pin
ADC_NEGATIVE_INPUT_PIN4
ADC4 pin
ADC_NEGATIVE_INPUT_PIN5
ADC5 pin
ADC_NEGATIVE_INPUT_PIN6
ADC6 pin
ADC_NEGATIVE_INPUT_PIN7
ADC7 pin
ADC_NEGATIVE_INPUT_GND
Internal ground
ADC_NEGATIVE_INPUT_IOGND
I/O ground
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7.5.10.
Enum adc_oversampling_and_decimation
Enum for the possible numbers of bits resolution can be increased by when using oversampling and
decimation.
Table 7-49. Members
Enum value
Description
ADC_OVERSAMPLING_AND_DECIMATION_DISABLE Don't use oversampling and decimation mode
7.5.11.
ADC_OVERSAMPLING_AND_DECIMATION_1BIT
1-bit resolution increase
ADC_OVERSAMPLING_AND_DECIMATION_2BIT
2-bit resolution increase
ADC_OVERSAMPLING_AND_DECIMATION_3BIT
3-bit resolution increase
ADC_OVERSAMPLING_AND_DECIMATION_4BIT
4-bit resolution increase
Enum adc_positive_input
Enum for the possible positive MUX input selections for the ADC.
Table 7-50. Members
Enum value
Description
ADC_POSITIVE_INPUT_PIN0
ADC0 pin
ADC_POSITIVE_INPUT_PIN1
ADC1 pin
ADC_POSITIVE_INPUT_PIN2
ADC2 pin
ADC_POSITIVE_INPUT_PIN3
ADC3 pin
ADC_POSITIVE_INPUT_PIN4
ADC4 pin
ADC_POSITIVE_INPUT_PIN5
ADC5 pin
ADC_POSITIVE_INPUT_PIN6
ADC6 pin
ADC_POSITIVE_INPUT_PIN7
ADC7 pin
ADC_POSITIVE_INPUT_PIN8
ADC8 pin
ADC_POSITIVE_INPUT_PIN9
ADC9 pin
ADC_POSITIVE_INPUT_PIN10
ADC10 pin
ADC_POSITIVE_INPUT_PIN11
ADC11 pin
ADC_POSITIVE_INPUT_PIN12
ADC12 pin
ADC_POSITIVE_INPUT_PIN13
ADC13 pin
ADC_POSITIVE_INPUT_PIN14
ADC14 pin
ADC_POSITIVE_INPUT_PIN15
ADC15 pin
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7.5.12.
Enum value
Description
ADC_POSITIVE_INPUT_PIN16
ADC16 pin
ADC_POSITIVE_INPUT_PIN17
ADC17 pin
ADC_POSITIVE_INPUT_PIN18
ADC18 pin
ADC_POSITIVE_INPUT_PIN19
ADC19 pin
ADC_POSITIVE_INPUT_TEMP
Temperature reference
ADC_POSITIVE_INPUT_BANDGAP
Bandgap voltage
ADC_POSITIVE_INPUT_SCALEDCOREVCC
1/4 scaled core supply
ADC_POSITIVE_INPUT_SCALEDIOVCC
1/4 scaled I/O supply
ADC_POSITIVE_INPUT_DAC
DAC input
Enum adc_reference
Enum for the possible reference voltages for the ADC.
Table 7-51. Members
7.5.13.
Enum value
Description
ADC_REFERENCE_INT1V
1.0V voltage reference
ADC_REFERENCE_INTVCC0
1/1.48VCC reference
ADC_REFERENCE_INTVCC1
1/2VCC (only for internal VCC > 2.1V)
ADC_REFERENCE_AREFA
External reference A
ADC_REFERENCE_AREFB
External reference B
Enum adc_resolution
Enum for the possible resolution values for the ADC.
Table 7-52. Members
Enum value
Description
ADC_RESOLUTION_12BIT
ADC 12-bit resolution
ADC_RESOLUTION_16BIT
ADC 16-bit resolution using oversampling and decimation
ADC_RESOLUTION_10BIT
ADC 10-bit resolution
ADC_RESOLUTION_8BIT
ADC 8-bit resolution
ADC_RESOLUTION_13BIT
ADC 13-bit resolution using oversampling and decimation
ADC_RESOLUTION_14BIT
ADC 14-bit resolution using oversampling and decimation
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Enum value
Description
ADC_RESOLUTION_15BIT
ADC 15-bit resolution using oversampling and decimation
ADC_RESOLUTION_CUSTOM ADC 16-bit result register for use with averaging. When using this
mode the ADC result register will be set to 16-bit wide, and the number
of samples to accumulate and the division factor is configured by the
adc_config::accumulate_samples and adc_config::divide_result
members in the configuration struct.
7.5.14.
Enum adc_window_mode
Enum for the possible window monitor modes for the ADC.
Table 7-53. Members
Enum value
Description
ADC_WINDOW_MODE_DISABLE
No window mode
ADC_WINDOW_MODE_ABOVE_LOWER
RESULT > WINLT
ADC_WINDOW_MODE_BELOW_UPPER
RESULT < WINUT
ADC_WINDOW_MODE_BETWEEN
WINLT < RESULT < WINUT
ADC_WINDOW_MODE_BETWEEN_INVERTED
!(WINLT < RESULT < WINUT)
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8.
Extra Information for ADC Driver
8.1.
Acronyms
Below is a table listing the acronyms used in this module, along with their intended meanings.
8.2.
Acronym
Description
ADC
Analog-to-Digital Converter
DAC
Digital-to-Analog Converter
LSB
Least Significant Bit
MSB
Most Significant Bit
DMA
Direct Memory Access
Dependencies
This driver has the following dependencies:
•
8.3.
System Pin Multiplexer Driver
Errata
There are no errata related to this driver.
8.4.
Module History
An overview of the module history is presented in the table below, with details on the enhancements and
fixes made to the module since its first release. The current version of this corresponds to the newest
version in the table.
Changelog
Added support for SAM R21
Added support for SAM D21 and new DMA quick start guide
Added ADC calibration constant loading from the device signature row when the module is initialized
Initial Release
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9.
Examples for ADC Driver
This is a list of the available Quick Start guides (QSGs) and example applications for SAM Analog-toDigital Converter (ADC) Driver. QSGs are simple examples with step-by-step instructions to configure
and use this driver in a selection of use cases. Note that a QSG can be compiled as a standalone
application or be added to the user application.
•
•
•
9.1.
Quick Start Guide for ADC - Basic
Quick Start Guide for ADC - Callback
Quick Start Guide for Using DMA with ADC/DAC
Quick Start Guide for ADC - Basic
In this use case, the ADC will be configured with the following settings:
•
1V from internal bandgap reference
•
Div 4 clock prescaler
•
12-bit resolution
•
Window monitor disabled
•
No gain
•
Positive input on ADC PIN x (depend on default configuration)
•
Negative input to GND (single ended)
•
Averaging disabled
•
Oversampling disabled
•
Right adjust data
•
Single-ended mode
•
Free running disabled
•
All events (input and generation) disabled
•
Sleep operation disabled
•
No reference compensation
•
No gain/offset correction
•
No added sampling time
•
Pin scan mode disabled
9.1.1.
Setup
9.1.1.1.
Prerequisites
There are no special setup requirements for this use-case.
9.1.1.2.
Code
Add to the main application source file, outside of any functions:
struct adc_module adc_instance;
Copy-paste the following setup code to your user application:
void configure_adc(void)
{
struct adc_config config_adc;
adc_get_config_defaults(&config_adc);
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#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
adc_enable(&adc_instance);
}
Add to user application initialization (typically the start of main()):
configure_adc();
9.1.1.3.
Workflow
1.
Create a module software instance structure for the ADC module to store the ADC driver state
while in use.
struct adc_module adc_instance;
2.
Note: This should never go out of scope as long as the module is in use. In most cases, this
should be global.
Configure the ADC module.
1.
Create an ADC module configuration struct, which can be filled out to adjust the configuration
of a physical ADC peripheral.
struct adc_config config_adc;
2.
Initialize the ADC configuration struct with the module's default values.
adc_get_config_defaults(&config_adc);
3.
Note: This should always be performed before using the configuration struct to ensure that
all values are initialized to known default settings.
Set ADC configurations.
#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
4.
Enable the ADC module so that conversions can be made.
adc_enable(&adc_instance);
9.1.2.
Use Case
9.1.2.1.
Code
Copy-paste the following code to your user application:
adc_start_conversion(&adc_instance);
uint16_t result;
do {
/* Wait for conversion to be done and read out result */
} while (adc_read(&adc_instance, &result) == STATUS_BUSY);
while (1) {
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/* Infinite loop */
}
9.1.2.2.
Workflow
1.
Start conversion.
adc_start_conversion(&adc_instance);
2.
Wait until conversion is done and read result.
uint16_t result;
do {
/* Wait for conversion to be done and read out result */
} while (adc_read(&adc_instance, &result) == STATUS_BUSY);
3.
Enter an infinite loop once the conversion is complete.
while (1) {
/* Infinite loop */
}
9.2.
Quick Start Guide for ADC - Callback
In this use case, the ADC will convert 128 samples using interrupt driven conversion. When all samples
have been sampled, a callback will be called that signals the main application that conversion is
complete.
The ADC will be set up as follows:
•
VCC /2 as reference
•
Div 8 clock prescaler
•
12-bit resolution
•
Window monitor disabled
•
1/2 gain
•
Positive input on ADC PIN 0
•
Negative input to GND (single ended)
•
Averaging disabled
•
Oversampling disabled
•
Right adjust data
•
Single-ended mode
•
Free running disabled
•
All events (input and generation) disabled
•
Sleep operation disabled
•
No reference compensation
•
No gain/offset correction
•
No added sampling time
•
Pin scan mode disabled
9.2.1.
Setup
9.2.1.1.
Prerequisites
There are no special setup requirements for this use-case.
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9.2.1.2.
Code
Add to the main application source file, outside of any functions:
struct adc_module adc_instance;
#define ADC_SAMPLES 128
uint16_t adc_result_buffer[ADC_SAMPLES];
Callback function:
volatile bool adc_read_done = false;
void adc_complete_callback(
struct adc_module *const module)
{
}
adc_read_done = true;
Copy-paste the following setup code to your user application:
void configure_adc(void)
{
struct adc_config config_adc;
adc_get_config_defaults(&config_adc);
#if (!SAML21) && (!SAML22) && (!SAMC21)
config_adc.gain_factor
= ADC_GAIN_FACTOR_DIV2;
#endif
config_adc.clock_prescaler = ADC_CLOCK_PRESCALER_DIV8;
config_adc.reference
= ADC_REFERENCE_INTVCC1;
#if (SAMC21)
config_adc.positive_input = ADC_POSITIVE_INPUT_PIN5;
#else
config_adc.positive_input = ADC_POSITIVE_INPUT_PIN6;
#endif
config_adc.resolution
= ADC_RESOLUTION_12BIT;
#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
}
adc_enable(&adc_instance);
void configure_adc_callbacks(void)
{
}
adc_register_callback(&adc_instance,
adc_complete_callback, ADC_CALLBACK_READ_BUFFER);
adc_enable_callback(&adc_instance, ADC_CALLBACK_READ_BUFFER);
Add to user application initialization (typically the start of main()):
configure_adc();
configure_adc_callbacks();
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9.2.1.3.
Workflow
1.
Create a module software instance structure for the ADC module to store the ADC driver state
while in use.
struct adc_module adc_instance;
2.
Note: This should never go out of scope as long as the module is in use. In most cases, this
should be global.
Create a buffer for the ADC samples to be stored in by the driver asynchronously.
#define ADC_SAMPLES 128
uint16_t adc_result_buffer[ADC_SAMPLES];
3.
Create a callback function that will be called each time the ADC completes an asynchronous read
job.
volatile bool adc_read_done = false;
void adc_complete_callback(
struct adc_module *const module)
{
}
4.
adc_read_done = true;
Configure the ADC module.
1. Create an ADC module configuration struct, which can be filled out to adjust the configuration
of a physical ADC peripheral.
struct adc_config config_adc;
2.
Initialize the ADC configuration struct with the module's default values.
adc_get_config_defaults(&config_adc);
3.
Note: This should always be performed before using the configuration struct to ensure that
all values are initialized to known default settings.
Change the ADC module configuration to suit the application.
#if (!SAML21) && (!SAML22) && (!SAMC21)
config_adc.gain_factor
= ADC_GAIN_FACTOR_DIV2;
#endif
config_adc.clock_prescaler = ADC_CLOCK_PRESCALER_DIV8;
config_adc.reference
= ADC_REFERENCE_INTVCC1;
#if (SAMC21)
config_adc.positive_input = ADC_POSITIVE_INPUT_PIN5;
#else
config_adc.positive_input = ADC_POSITIVE_INPUT_PIN6;
#endif
config_adc.resolution
= ADC_RESOLUTION_12BIT;
4.
Set ADC configurations.
#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
5.
Enable the ADC module so that conversions can be made.
adc_enable(&adc_instance);
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5.
Register and enable the ADC Read Buffer Complete callback handler.
1. Register the user-provided Read Buffer Complete callback function with the driver, so that it
will be run when an asynchronous buffer read job completes.
adc_register_callback(&adc_instance,
adc_complete_callback, ADC_CALLBACK_READ_BUFFER);
2.
Enable the Read Buffer Complete callback so that it will generate callbacks.
adc_enable_callback(&adc_instance, ADC_CALLBACK_READ_BUFFER);
9.2.2.
Use Case
9.2.2.1.
Code
Copy-paste the following code to your user application:
system_interrupt_enable_global();
adc_read_buffer_job(&adc_instance, adc_result_buffer, ADC_SAMPLES);
while (adc_read_done == false) {
/* Wait for asynchronous ADC read to complete */
}
while (1) {
/* Infinite loop */
}
9.2.2.2.
Workflow
1.
Enable global interrupts, so that callbacks can be generated by the driver.
system_interrupt_enable_global();
2.
Start an asynchronous ADC conversion, to store ADC samples into the global buffer and generate
a callback when complete.
adc_read_buffer_job(&adc_instance, adc_result_buffer, ADC_SAMPLES);
3.
Wait until the asynchronous conversion is complete.
while (adc_read_done == false) {
/* Wait for asynchronous ADC read to complete */
}
4.
Enter an infinite loop once the conversion is complete.
while (1) {
/* Infinite loop */
}
9.3.
Quick Start Guide for Using DMA with ADC/DAC
The supported board list:
•
SAM D21 Xplained Pro
•
SAM D11 Xplained Pro
•
SAM L21 Xplained Pro
•
SAM DA1 Xplained Pro
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•
SAM C21 Xplained Pro
This quick start will convert an analog input signal from AIN4 and output the converted value to DAC on
PA2. The data between ADC and DAC with be transferred through DMA instead of a CPU intervene.
The ADC will be configured with the following settings:
•
1/2 VDDANA
•
Div 16 clock prescaler
•
10-bit resolution
•
Window monitor disabled
•
•
•
•
•
•
•
•
•
•
•
•
•
No gain
Positive input on ADC AIN4
Averaging disabled
Oversampling disabled
Right adjust data
Single-ended mode
Free running enable
All events (input and generation) disabled
Sleep operation disabled
No reference compensation
No gain/offset correction
No added sampling time
Pin scan mode disabled
The DAC will be configured with the following settings:
•
Analog VCC as reference
•
Internal output disabled
•
Drive the DAC output to PA2
•
Right adjust data
•
The output buffer is disabled when the chip enters STANDBY sleep mode
The DMA will be configured with the following settings:
•
Move data from peripheral to peripheral
•
Using ADC result ready trigger
•
Using DMA priority level 0
•
Beat transfer will be triggered on each trigger
•
Loopback descriptor for DAC conversion
9.3.1.
Setup
9.3.1.1.
Prerequisites
There are no special setup requirements for this use-case.
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9.3.1.2.
Code
Add to the main application source file, outside of any functions:
struct dac_module dac_instance;
struct adc_module adc_instance;
struct dma_resource example_resource;
COMPILER_ALIGNED(16)
DmacDescriptor example_descriptor SECTION_DMAC_DESCRIPTOR;
Copy-paste the following setup code to your user application:
void configure_adc(void)
{
struct adc_config config_adc;
adc_get_config_defaults(&config_adc);
#if !(SAML21)
#if !(SAMC21)
config_adc.gain_factor
#endif
config_adc.resolution
#endif
config_adc.clock_prescaler
config_adc.reference
config_adc.positive_input
config_adc.freerunning
config_adc.left_adjust
= ADC_GAIN_FACTOR_DIV2;
= ADC_RESOLUTION_10BIT;
=
=
=
=
=
ADC_CLOCK_PRESCALER_DIV16;
ADC_REFERENCE_INTVCC1;
ADC_POSITIVE_INPUT_PIN4;
true;
false;
#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
}
adc_enable(&adc_instance);
void configure_dac(void)
{
struct dac_config config_dac;
dac_get_config_defaults(&config_dac);
#if (SAML21)
config_dac.reference = DAC_REFERENCE_INTREF;
#else
config_dac.reference = DAC_REFERENCE_AVCC;
#endif
dac_init(&dac_instance, DAC, &config_dac);
}
void configure_dac_channel(void)
{
struct dac_chan_config config_dac_chan;
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dac_chan_get_config_defaults(&config_dac_chan);
dac_chan_set_config(&dac_instance, DAC_CHANNEL_0, &config_dac_chan);
}
dac_chan_enable(&dac_instance, DAC_CHANNEL_0);
void configure_dma_resource(struct dma_resource *resource)
{
struct dma_resource_config config;
dma_get_config_defaults(&config);
#if (SAMC21)
config.peripheral_trigger = ADC1_DMAC_ID_RESRDY;
#else
config.peripheral_trigger = ADC_DMAC_ID_RESRDY;
#endif
config.trigger_action = DMA_TRIGGER_ACTON_BEAT;
}
dma_allocate(resource, &config);
void setup_transfer_descriptor(DmacDescriptor *descriptor)
{
struct dma_descriptor_config descriptor_config;
dma_descriptor_get_config_defaults(&descriptor_config);
descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
descriptor_config.dst_increment_enable = false;
descriptor_config.src_increment_enable = false;
descriptor_config.block_transfer_count = 1000;
descriptor_config.source_address = (uint32_t)(&adc_instance.hw>RESULT.reg);
#if (SAML21)
descriptor_config.destination_address = (uint32_t)(&dac_instance.hw>DATA[DAC_CHANNEL_0].reg);
#else
descriptor_config.destination_address = (uint32_t)(&dac_instance.hw>DATA.reg);
#endif
descriptor_config.next_descriptor_address = (uint32_t)descriptor;
}
dma_descriptor_create(descriptor, &descriptor_config);
Add to user application initialization (typically the start of main()):
configure_adc();
configure_dac();
configure_dac_channel();
dac_enable(&dac_instance);
configure_dma_resource(&example_resource);
setup_transfer_descriptor(&example_descriptor);
dma_add_descriptor(&example_resource, &example_descriptor);
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9.3.1.3.
Workflow
Configure the ADC
1.
Create a module software instance structure for the ADC module to store the ADC driver state
while it is in use.
struct adc_module adc_instance;
Note: This should never go out of scope as long as the module is in use. In most cases, this
should be global.
2.
Configure the ADC module.
1. Create an ADC module configuration struct, which can be filled out to adjust the configuration
of a physical ADC peripheral.
struct adc_config config_adc;
2.
Initialize the ADC configuration struct with the module's default values.
adc_get_config_defaults(&config_adc);
3.
Note: This should always be performed before using the configuration struct to ensure that
all values are initialized to known default settings.
Set extra configurations.
#if !(SAML21)
#if !(SAMC21)
config_adc.gain_factor
#endif
config_adc.resolution
#endif
config_adc.clock_prescaler
config_adc.reference
config_adc.positive_input
config_adc.freerunning
config_adc.left_adjust
4.
= ADC_GAIN_FACTOR_DIV2;
= ADC_RESOLUTION_10BIT;
=
=
=
=
=
ADC_CLOCK_PRESCALER_DIV16;
ADC_REFERENCE_INTVCC1;
ADC_POSITIVE_INPUT_PIN4;
true;
false;
Set ADC configurations.
#if (SAMC21)
adc_init(&adc_instance, ADC1, &config_adc);
#else
adc_init(&adc_instance, ADC, &config_adc);
#endif
5.
Enable the ADC module so that conversions can be made.
adc_enable(&adc_instance);
Configure the DAC
1.
Create a module software instance structure for the DAC module to store the DAC driver state
while it is in use.
struct dac_module dac_instance;
2.
Note: This should never go out of scope as long as the module is in use. In most cases, this
should be global.
Configure the DAC module.
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1.
Create a DAC module configuration struct, which can be filled out to adjust the configuration
of a physical DAC peripheral.
struct dac_config config_dac;
2.
Initialize the DAC configuration struct with the module's default values.
dac_get_config_defaults(&config_dac);
3.
Note: This should always be performed before using the configuration struct to ensure that
all values are initialized to known default settings.
Set extra DAC configurations.
#if (SAML21)
config_dac.reference = DAC_REFERENCE_INTREF;
#else
config_dac.reference = DAC_REFERENCE_AVCC;
#endif
4.
Set DAC configurations to DAC instance.
dac_init(&dac_instance, DAC, &config_dac);
5.
Enable the DAC module so that channels can be configured.
dac_enable(&dac_instance);
3.
Configure the DAC channel.
1. Create a DAC channel configuration struct, which can be filled out to adjust the configuration
of a physical DAC output channel.
struct dac_chan_config config_dac_chan;
2.
Initialize the DAC channel configuration struct with the module's default values.
dac_chan_get_config_defaults(&config_dac_chan);
3.
Note: This should always be performed before using the configuration struct to ensure that
all values are initialized to known default settings.
Configure the DAC channel with the desired channel settings.
dac_chan_set_config(&dac_instance, DAC_CHANNEL_0,
&config_dac_chan);
4.
Enable the DAC channel so that it can output a voltage.
dac_chan_enable(&dac_instance, DAC_CHANNEL_0);
Configure the DMA
1.
Create a DMA resource configuration structure, which can be filled out to adjust the configuration of
a single DMA transfer.
struct dma_resource_config config;
2.
Initialize the DMA resource configuration struct with the module's default values.
dma_get_config_defaults(&config);
Note: This should always be performed before using the configuration struct to ensure that all
values are initialized to known default settings.
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3.
Set extra configurations for the DMA resource. ADC_DMAC_ID_RESRDY trigger causes a beat
transfer in this example.
#if (SAMC21)
config.peripheral_trigger = ADC1_DMAC_ID_RESRDY;
#else
config.peripheral_trigger = ADC_DMAC_ID_RESRDY;
#endif
config.trigger_action = DMA_TRIGGER_ACTON_BEAT;
4.
Allocate a DMA resource with the configurations.
dma_allocate(resource, &config);
5.
Create a DMA transfer descriptor configuration structure, which can be filled out to adjust the
configuration of a single DMA transfer.
struct dma_descriptor_config descriptor_config;
6.
Initialize the DMA transfer descriptor configuration struct with the module's default values.
dma_descriptor_get_config_defaults(&descriptor_config);
7.
Note: This should always be performed before using the configuration struct to ensure that all
values are initialized to known default settings.
Set the specific parameters for a DMA transfer with transfer size, source address, and destination
address.
descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
descriptor_config.dst_increment_enable = false;
descriptor_config.src_increment_enable = false;
descriptor_config.block_transfer_count = 1000;
descriptor_config.source_address = (uint32_t)(&adc_instance.hw>RESULT.reg);
#if (SAML21)
descriptor_config.destination_address = (uint32_t)
(&dac_instance.hw->DATA[DAC_CHANNEL_0].reg);
#else
descriptor_config.destination_address = (uint32_t)
(&dac_instance.hw->DATA.reg);
#endif
descriptor_config.next_descriptor_address = (uint32_t)descriptor;
8.
Create the DMA transfer descriptor.
dma_descriptor_create(descriptor, &descriptor_config);
9.
Add DMA descriptor to DMA resource.
dma_add_descriptor(&example_resource, &example_descriptor);
9.3.2.
Use Case
9.3.2.1.
Code
Copy-paste the following code to your user application:
adc_start_conversion(&adc_instance);
dma_start_transfer_job(&example_resource);
while (true) {
}
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9.3.2.2.
Workflow
1.
Start ADC conversion.
adc_start_conversion(&adc_instance);
2.
Start the transfer job.
dma_start_transfer_job(&example_resource);
3.
Enter endless loop.
while (true) {
}
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10.
Document Revision History
Doc. Rev. Date
Comments
42109E
12/2015 Added support for SAM DA1 and SAM D09
42109D
12/2014 Added support for SAM R21 and SAM D10/D11
42109C
01/2014 Added support for SAM D21
42109B
06/2013 Added additional documentation on the event system. Corrected documentation
typos.
42109A
06/2013 Initial release
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