SMART ARM-based Microcontrollers
AT13481: SAM Frequency Meter (FREQM) Driver
APPLICATION NOTE
Introduction
®
®
This driver for Atmel | SMART ARM -based microcontrollers provides an
interface for the configuration and management of the device's Frequency
Meter functionality.
The following driver API modes are covered by this manual:
•
Polled APIs
•
Callback APIs
The following peripheral is used by this module:
•
FREQM (Frequency Meter)
The following devices can use this module:
•
Atmel | SMART SAM L22
•
Atmel | SMART SAM C20
•
Atmel | SMART SAM C21
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
4. Special Considerations.............................................................................................. 7
5. Extra Information....................................................................................................... 8
6. Examples................................................................................................................... 9
7. API Overview........................................................................................................... 10
7.1.
7.2.
7.3.
7.4.
Variable and Type Definitions..................................................................................................... 10
7.1.1.
Type freqm_callback_t.................................................................................................10
7.1.2.
Variable _freqm_instance............................................................................................ 10
Structure Definitions................................................................................................................... 10
7.2.1.
Struct freqm_config......................................................................................................10
7.2.2.
Struct freqm_module................................................................................................... 10
Function Definitions....................................................................................................................10
7.3.1.
Driver Initialization and Configuration.......................................................................... 10
7.3.2.
Read FREQM Result................................................................................................... 12
7.3.3.
Callback Configuration and Initialization......................................................................13
7.3.4.
Callback Enabling and Disabling................................................................................. 14
7.3.5.
Function freqm_is_syncing()........................................................................................15
Enumeration Definitions............................................................................................................. 15
7.4.1.
Enum freqm_callback.................................................................................................. 15
7.4.2.
Enum freqm_callback_type......................................................................................... 16
7.4.3.
Enum freqm_status......................................................................................................16
8. Extra Information for FREQM Driver........................................................................17
8.1.
8.2.
8.3.
Acronyms....................................................................................................................................17
Dependencies.............................................................................................................................17
Errata..........................................................................................................................................17
8.4.
Module History............................................................................................................................17
9. Examples for FREQM Driver................................................................................... 18
9.1.
9.2.
Quick Start Guide for FREQM - Basic........................................................................................18
9.1.1.
Setup........................................................................................................................... 18
9.1.2.
Implementation............................................................................................................ 19
Quick Start Guide for FREQM - Callback................................................................................... 20
9.2.1.
Setup........................................................................................................................... 20
9.2.2.
Implementation............................................................................................................ 22
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10. Document Revision History..................................................................................... 24
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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
The module accurately measures the frequency of a clock by comparing it to a known reference clock as
soon as the FREQM is enabled. Two generic clocks are used by the FREQM. The frequency of the
measured clock is:
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Ratio can be measured with 24-bit accuracy.
The FREQM has one interrupt source, which generates when a frequency measurement is done. It can
be used to wake up the device from sleep modes.
This driver provides an interface for the FREQM functions on the device.
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4.
Special Considerations
There are no special considerations for this module.
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5.
Extra Information
For extra information see Extra Information for FREQM 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 FREQM Driver.
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7.
API Overview
7.1.
Variable and Type Definitions
7.1.1.
Type freqm_callback_t
typedef void(* freqm_callback_t )(void)
Type definition for a FREQM module callback function.
7.1.2.
Variable _freqm_instance
struct freqm_module * _freqm_instance
7.2.
Structure Definitions
7.2.1.
Struct freqm_config
Configuration structure for a Frequency Meter.
Table 7-1 Members
Type
Name
Description
enum gclk_generator msr_clock_source GCLK source select for measurement
uint16_t
ref_clock_circles
enum gclk_generator ref_clock_source
7.2.2.
Measurement duration in number of reference clock cycles.
Range 1~255
GCLK source select for reference
Struct freqm_module
FREQM 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.
7.3.
Function Definitions
7.3.1.
Driver Initialization and Configuration
7.3.1.1.
Function freqm_init()
Initializes a hardware FREQM module instance.
enum status_code freqm_init(
struct freqm_module *const module_inst,
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Freqm *const hw,
struct freqm_config *const config)
Enables the clock and initializes the FREQM module, based on the given configuration values.
Table 7-2 Parameters
Data direction
Parameter name
Description
[in, out]
module_inst
Pointer to the software module instance struct
[in]
hw
Pointer to the FREQM hardware module
[in]
config
Pointer to the FREQM configuration options struct
Returns
Status of the initialization procedure.
Table 7-3 Return Values
7.3.1.2.
Return value
Description
STATUS_OK
The module was initialized successfully
Function freqm_get_config_defaults()
Initializes all members of a FREQM configuration structure to safe defaults.
void freqm_get_config_defaults(
struct freqm_config *const config)
Initializes all members of a given Frequency Meter configuration structure to safe known default values.
This function should be called on all new instances of these configuration structures before being
modified by the user application.
The default configuration is as follows:
•
Measurement clock source is GCLK0
•
Reference clock source is GCLK1
•
Frequency Meter Reference Clock Cycles 127
Table 7-4 Parameters
7.3.1.3.
Data direction
Parameter name
Description
[in]
config
Configuration structure to initialize to default values
Function freqm_enable()
Enables a FREQM that was previously configured.
void freqm_enable(
struct freqm_module *const module_inst)
Enables Frequency Meter that was previously configured via a call to freqm_init().
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Table 7-5 Parameters
7.3.1.4.
Data direction
Parameter name
Description
[in]
module_inst
Software instance for the Frequency Meter peripheral
Function freqm_disable()
Disables a FREQM that was previously enabled.
void freqm_disable(
struct freqm_module *const module_inst)
Disables Frequency Meter that was previously started via a call to freqm_enable().
Table 7-6 Parameters
Data direction
Parameter name
Description
[in]
module_inst
Software instance for the Frequency Meter peripheral
7.3.2.
Read FREQM Result
7.3.2.1.
Function freqm_start_measure()
Start a manual measurement process.
void freqm_start_measure(
struct freqm_module *const module)
Table 7-7 Parameters
7.3.2.2.
Data direction
Parameter name
Description
[in]
module
Pointer to the FREQM software instance struct
Function freqm_clear_overflow()
Clears module overflow flag.
void freqm_clear_overflow(
struct freqm_module *const module)
Clears the overflow flag of the module.
Table 7-8 Parameters
7.3.2.3.
Data direction
Parameter name
Description
[in]
module
Pointer to the FREQM software instance struct
Function freqm_get_result_value()
Read the measurement data result.
enum freqm_status freqm_get_result_value(
struct freqm_module *const module_inst,
uint32_t * result)
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Reads the measurement data result.
Table 7-9 Parameters
Data direction
Parameter name
Description
[in]
module_inst
Pointer to the FREQM software instance struct
[out]
result
Pointer to store the result value in
Note: If overflow occurred, configure faster reference clock or reduce reference clock cycles.
Returns
Status of the FREQM read request.
Table 7-10 Return Values
Return value
Description
FREQM_STATUS_MEASURE_DONE
Measurement result was retrieved successfully
FREQM_STATUS_MEASURE_BUSY
Measurement result was not ready
FREQM_STATUS_CNT_OVERFLOW
Measurement result was overflow
7.3.3.
Callback Configuration and Initialization
7.3.3.1.
Function freqm_register_callback()
Registers a callback.
enum status_code freqm_register_callback(
struct freqm_module *const module,
freqm_callback_t callback_func,
enum freqm_callback callback_type)
Registers a callback function which is implemented by the user.
Note: The callback must be enabled by freqm_enable_callback, in order for the interrupt handler to call
it when the conditions for the callback type is met.
Table 7-11 Parameters
Data direction
Parameter name
Description
[in]
module
Pointer to FREQM software instance struct
[in]
callback_func
Pointer to callback function
[in]
callback_type
Callback type given by an enum
Table 7-12 Return Values
Return value
Description
STATUS_OK
The function exited successfully
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7.3.3.2.
Function freqm_unregister_callback()
Unregisters a callback.
enum status_code freqm_unregister_callback(
struct freqm_module * module,
enum freqm_callback callback_type)
Unregisters a callback function implemented by the user. The callback should be disabled before it is
unregistered.
Table 7-13 Parameters
Data direction
Parameter name
Description
[in]
module
Pointer to FREQM software instance struct
[in]
callback_type
Callback type given by an enum
Table 7-14 Return Values
Return value
Description
STATUS_OK
The function exited successfully
7.3.4.
Callback Enabling and Disabling
7.3.4.1.
Function freqm_enable_callback()
Enable an FREQM callback.
enum status_code freqm_enable_callback(
struct freqm_module *const module,
const enum freqm_callback_type type)
Table 7-15 Parameters
Data direction
Parameter name
Description
[in, out]
module
Pointer to the software instance struct
[in]
type
Callback source type
Returns
Status of the callback enable operation.
Table 7-16 Return Values
Return value
Description
STATUS_OK
The callback was enabled successfully
STATUS_ERR_INVALID_ARG
If an invalid callback type was supplied
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7.3.4.2.
Function freqm_disable_callback()
Disable an FREQM callback.
enum status_code freqm_disable_callback(
struct freqm_module *const module,
const enum freqm_callback_type type)
Table 7-17 Parameters
Data direction
Parameter name
Description
[in, out]
module
Pointer to the software instance struct
[in]
type
Callback source type
Returns
Status of the callback enable operation.
Table 7-18 Return Values
7.3.5.
Return value
Description
STATUS_OK
The callback was enabled successfully
STATUS_ERR_INVALID_ARG
If an invalid callback type was supplied
Function freqm_is_syncing()
Determines if the hardware module(s) are currently synchronizing to the bus.
bool freqm_is_syncing( void )
Checks to see if the underlying hardware peripheral module(s) are currently synchronizing across multiple
clock domains to the hardware bus. This function can be used to delay further operations on a module
until such time that it is ready, to prevent blocking delays for synchronization in the user application.
Returns
Synchronization status of the underlying hardware module(s).
Table 7-19 Return Values
Return value
Description
false
If the module has completed synchronization
true
If the module synchronization is ongoing
7.4.
Enumeration Definitions
7.4.1.
Enum freqm_callback
Enum for possible callback types for the FREQM module.
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Table 7-20 Members
7.4.2.
Enum value
Description
FREQM_CALLBACK_DONE
Callback for measurement done
Enum freqm_callback_type
FREQM callback type.
Table 7-21 Members
7.4.3.
Enum value
Description
FREQM_CALLBACK_MEASURE_DONE
Measurement done callback.
Enum freqm_status
Enum for the possible status types for the FREQM module.
Table 7-22 Members
Enum value
Description
FREQM_STATUS_MEASURE_DONE
FREQM measurement is finish
FREQM_STATUS_MEASURE_BUSY
FREQM measurement is ongoing or not
FREQM_STATUS_CNT_OVERFLOW
FREQM sticky count value overflow
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8.
Extra Information for FREQM Driver
8.1.
Acronyms
Below is a table listing the acronyms used in this module, along with their intended meanings.
8.2.
Acronym
Description
FREQM
Frequency Meter
Dependencies
This driver has no dependencies.
8.3.
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
Initial Release
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9.
Examples for FREQM Driver
This is a list of the available Quick Start guides (QSGs) and example applications for SAM Frequency
Meter (FREQM) 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 FREQM - Basic
Quick Start Guide for FREQM - Callback
Quick Start Guide for FREQM - Basic
In this use case, the Frequency Meter (FREQM) module is configured for:
•
The FREQM peripheral will not be stopped in standby sleep mode.
This use case will read measurement data in polling mode repeatly. After reading a data, the board LED
will be toggled.
9.1.1.
Setup
9.1.1.1.
Prerequisites
There are no special setup requirements for this use-case.
9.1.1.2.
Code
Copy-paste the following setup code to your user application:
/* FREQM module software instance (must not go out of scope while in use)
*/
static struct freqm_module freqm_instance;
void configure_freqm(void)
{
/* Create a new configuration structure for the FREQM settings
* and fill with the default module settings. */
struct freqm_config config_freqm;
freqm_get_config_defaults(&config_freqm);
/* Alter any FREQM configuration settings here if required */
}
/* Initialize FREQM with the user settings */
freqm_init(&freqm_instance, FREQM, &config_freqm);
Add to user application initialization (typically the start of main()):
system_init();
configure_freqm();
freqm_enable(&freqm_instance);
9.1.1.3.
Workflow
1.
Create an FREQM device instance struct, which will be associated with a FREQM peripheral
hardware instance.
static struct freqm_module freqm_instance;
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2.
Note: Device instance structures shall never go out of scope when in use.
Create a new function configure_freqm(), which will be used to configure the overall FREQM
peripheral.
void configure_freqm(void)
3.
Create an FREQM peripheral configuration structure that will be filled out to set the module
configuration.
struct freqm_config config_freqm;
4.
Fill the FREQM peripheral configuration structure with the default module configuration values.
freqm_get_config_defaults(&config_freqm);
5.
Initialize the FREQM peripheral and associate it with the software instance structure that was
defined previously.
freqm_init(&freqm_instance, FREQM, &config_freqm);
6.
Enable the now initialized FREQM peripheral.
freqm_enable(&freqm_instance);
9.1.2.
Implementation
9.1.2.1.
Code
Copy-paste the following code to your user application:
uint32_t measure_result;
enum freqm_status status;
freqm_start_measure(&freqm_instance);
while ((status = freqm_get_result_value(&freqm_instance, &measure_result))
== FREQM_STATUS_MEASURE_BUSY) {
};
switch(status) {
case FREQM_STATUS_MEASURE_DONE:
LED_On(LED_0_PIN);
while (true) {
}
case FREQM_STATUS_CNT_OVERFLOW:
freqm_clear_overflow(&freqm_instance);
while (true) {
LED_Toggle(LED_0_PIN);
volatile uint32_t delay = 50000;
while(delay--) {
}
}
default:
Assert(false);
break;
}
9.1.2.2.
Workflow
1.
Start FREQM measurement and wait until measure done then read result data.
freqm_start_measure(&freqm_instance);
while ((status = freqm_get_result_value(&freqm_instance,
&measure_result))
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};
2.
== FREQM_STATUS_MEASURE_BUSY) {
The board LED is on to indicate a measurement data is read.
case FREQM_STATUS_MEASURE_DONE:
LED_On(LED_0_PIN);
while (true) {
}
3.
The board LED is toggle to indicate measurement is overflow.
case FREQM_STATUS_CNT_OVERFLOW:
freqm_clear_overflow(&freqm_instance);
while (true) {
LED_Toggle(LED_0_PIN);
volatile uint32_t delay = 50000;
while(delay--) {
}
}
9.2.
Quick Start Guide for FREQM - Callback
In this use case, the Frequency Meter (FREQM) module is configured for:
•
The FREQM peripheral will not be stopped in standby sleep mode.
This use case will read measurement data in interrupt mode repeatly. After reading specific size of buffer
data, the board LED will be toggled.
9.2.1.
Setup
9.2.1.1.
Prerequisites
There are no special setup requirements for this use-case.
9.2.1.2.
Code
Copy-paste the following setup code to your user application:
bool volatile freqm_read_done = false;
void configure_freqm(void);
void configure_freqm_callback(void);
void freqm_complete_callback(void);
/* FREQM module software instance (must not go out of scope while in use)
*/
static struct freqm_module freqm_instance;
void configure_freqm(void)
{
/* Create a new configuration structure for the FREQM settings
* and fill with the default module settings. */
struct freqm_config config_freqm;
freqm_get_config_defaults(&config_freqm);
config_freqm.ref_clock_circles = 255;
/* Alter any FREQM configuration settings here if required */
/* Initialize FREQM with the user settings */
freqm_init(&freqm_instance, FREQM, &config_freqm);
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}
void freqm_complete_callback(void)
{
freqm_read_done = true;
}
void configure_freqm_callback(void)
{
freqm_register_callback(&freqm_instance, freqm_complete_callback,
FREQM_CALLBACK_MEASURE_DONE);
freqm_enable_callback(&freqm_instance, FREQM_CALLBACK_MEASURE_DONE);
}
Add to user application initialization (typically the start of main()):
system_init();
configure_freqm();
configure_freqm_callback();
freqm_enable(&freqm_instance);
9.2.1.3.
Workflow
1.
Create an FREQM device instance struct, which will be associated with an FREQM peripheral
hardware instance.
static struct freqm_module freqm_instance;
2.
Note: Device instance structures shall never go out of scope when in use.
Create a new function configure_freqm(), which will be used to configure the overall FREQM
peripheral.
void configure_freqm(void)
3.
Create an FREQM peripheral configuration structure that will be filled out to set the module
configuration.
struct freqm_config config_freqm;
4.
Fill the FREQM peripheral configuration structure with the default module configuration values.
freqm_get_config_defaults(&config_freqm);
config_freqm.ref_clock_circles = 255;
5.
Initialize the FREQM peripheral and associate it with the software instance structure that was
defined previously.
freqm_init(&freqm_instance, FREQM, &config_freqm);
6.
Create a new callback function.
void freqm_complete_callback(void)
{
freqm_read_done = true;
}
7.
Create a callback status software flag.
bool volatile freqm_read_done = false;
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8.
Let the callback function set the flag to true when read job done.
freqm_read_done = true;
9.
Create a new function configure_freqm_callback(), which will be used to configure the
callbacks.
void configure_freqm_callback(void)
{
freqm_register_callback(&freqm_instance, freqm_complete_callback,
FREQM_CALLBACK_MEASURE_DONE);
freqm_enable_callback(&freqm_instance,
FREQM_CALLBACK_MEASURE_DONE);
}
10. Register callback function.
freqm_register_callback(&freqm_instance, freqm_complete_callback,
FREQM_CALLBACK_MEASURE_DONE);
11. Enable the callbacks.
freqm_enable_callback(&freqm_instance, FREQM_CALLBACK_MEASURE_DONE);
12. Enable the now initialized FREQM peripheral.
freqm_enable(&freqm_instance);
Note: This should not be done until after the FREQM is setup and ready to be used.
9.2.2.
Implementation
9.2.2.1.
Code
Copy-paste the following code to your user application:
uint32_t measure_result;
enum freqm_status status;
freqm_start_measure(&freqm_instance);
while (!freqm_read_done) {
}
status = freqm_get_result_value(&freqm_instance, &measure_result);
switch(status) {
case FREQM_STATUS_MEASURE_DONE:
LED_On(LED_0_PIN);
while (true) {
}
case FREQM_STATUS_CNT_OVERFLOW:
freqm_clear_overflow(&freqm_instance);
while (true) {
LED_Toggle(LED_0_PIN);
volatile uint32_t delay = 50000;
while(delay--) {
}
}
default:
Assert(false);
break;
}
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9.2.2.2.
Workflow
1.
Start an asynchronous FREQM read job, to store measurement data into the global buffer and
generate a callback when complete.
freqm_start_measure(&freqm_instance);
2.
Wait until the asynchronous read job is complete.
while (!freqm_read_done) {
}
status = freqm_get_result_value(&freqm_instance, &measure_result);
3.
The board LED on to indicate measurement data read.
case FREQM_STATUS_MEASURE_DONE:
LED_On(LED_0_PIN);
while (true) {
}
4.
The board LED toggled to indicate measurement overflow occous.
case FREQM_STATUS_CNT_OVERFLOW:
freqm_clear_overflow(&freqm_instance);
while (true) {
LED_Toggle(LED_0_PIN);
volatile uint32_t delay = 50000;
while(delay--) {
}
}
Atmel AT13481: SAM Frequency Meter (FREQM) Driver [APPLICATION NOTE]
Atmel-42506A-SAM-Frequency-Meter-(FREQM)-Driver_AT13481_Application Note-08/2015
23
10.
Document Revision History
Doc. Rev.
Date
Comments
42506A
08/2015
Initial document release
Atmel AT13481: SAM Frequency Meter (FREQM) Driver [APPLICATION NOTE]
Atmel-42506A-SAM-Frequency-Meter-(FREQM)-Driver_AT13481_Application Note-08/2015
24
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