View detail for Single-slope PWM Implementation using SAM D21 TCC in a Touch-based Application

TRAINING MANUAL
Single-slope PWM Implementation using SAM D21 TCC in
a Touch-based Application
AN-9232
Prerequisites
• Hardware Prerequisites
• Atmel® SAM D21 Xplained Pro Evaluation Kit
• Atmel QT1 Xplained Pro Kit
• USB Micro Cable (TypeA/Micro-B)
• Software Prerequisites
• Atmel Studio 6.2 or higher
• Atmel Software Framework 3.17.0 or higher
• Atmel QTouch® Composer 5.3 or higher
• Atmel QTouch Library 5.3 or higher
• Documentation Prerequisites
• Atmel-42271-Introduction-to-QTouch-Design-Parameters-using-
SAM-D21-Xplained-Pro_Training-Manual_AN-7846 Training Manual
• Estimated completion time: 60min.
Introduction
The goal of this hands-on is to:
• Create a Touch project using QTouch Project Builder
• Use QTouch Analyzer to test the project
• Implement a PWM signal using the SAM D21 Timer/Counters for Control
peripheral (TCC) to drive the brightness of a LED
• Modify the LED brightness in relation to the Touch Delta value of a Button
sensor by updating the PWM duty cycle
42327A−07/2014
Table of Contents
Prerequisites .....................................................................................1
Introduction .......................................................................................1
Icon Key Identifiers ...........................................................................3
1.
Training Module Architecture .....................................................4
1.1
Atmel Studio Extension (.vsix) ............................................................. 4
1.2
Atmel Training Executable (.exe) ......................................................... 4
2.
Introduction ................................................................................5
3.
Assignment 1: Create a Touch project using QTouch Project
Builder ........................................................................................6
4.
5.
6.
3.1
Project Creation ................................................................................... 6
3.2
Conclusion ......................................................................................... 18
Assignment 2: Use QTouch Analyzer to Test the Project ........19
4.1
Connect the Kit to QTouch Analyzer ................................................. 19
4.2
Test the Proximity Effect of the QTouch Application ......................... 23
4.3
Conclusion ......................................................................................... 24
Assignment 3: Implement a PWM Signal using the SAM D21
Timer/Counters for Control Application Peripheral (TCC) ........25
5.1
Introduction to Timer/Counters for Control Application (TCC) ........... 25
5.2
TCC Peripheral Initialization Using ASF Quick Start Guide. ............. 27
5.3
Conclusion ......................................................................................... 34
Assignment 4: Use QTouch Button to Control LED Brightness35
6.1
Reading and using Button Touch Delta Value ................................... 35
6.2
Using PWM to Control LED Brightness ............................................. 37
6.3
Conclusion ......................................................................................... 41
7.
Conclusion ...............................................................................42
8.
Revision History .......................................................................43
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Icon Key Identifiers
Delivers contextual information about a specific topic.
Highlights useful tips and techniques.
Highlights objectives to be completed.
Highlights the expected result of an assignment step.
Indicates important information.
Highlights actions to be executed out of the target when
necessary.
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1.
Training Module Architecture
This training material can be retrieved through different Atmel deliveries:
•
As an Atmel Studio Extension (.vsix file) usually found on the Atmel Gallery web site
(http://gallery.atmel.com/) or using the Atmel Studio Extension manager
•
As an Atmel Training Executable (.exe file) usually provided during Atmel Training sessions
Depending on the delivery type, the different resources needed by this training material (hands-on
documentation, datasheets, application notes, software, and tools) will be found on different locations.
1.1
Atmel Studio Extension (.vsix)
Once the extension installed, you can open and create the different projects using “New Example Project
from ASF..." in Atmel Studio.
The projects installed from an extension are usually under “Atmel Training >
Atmel Corp. Extension Name”.
There are different projects which can be available depending on the extension:
•
•
•
Hands-on Documentation: contains the documentation as required resources
Hands-on Assignment: contains the initial project that may be required to start
Hands-on Solution: contains the final application which is a solution for this hands-on
Each time a reference is made to some resources in the following pages, the user
must refer to the Hands-on Documentation project folder.
1.2
Atmel Training Executable (.exe)
Depending where the executable has been installed, you will find the following architecture which is
composed by two main folders:
•
•
AN-XXXX_Hands-on: contains the initial project that may be required to start and a solution
Resources: contains required resources (datasheets, software, and tools…)
Unless a specific location is specified, each time a reference is made to some
resources in the following pages, the user must refer to this Resources folder.
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2.
Introduction
This hands-on will focus on the development of a simple Touch application that uses a Button sensor from the
Atmel QT1 Xplained Pro Self Capacitance extension board to modify the brightness of a LED.
The LED brightness is controlled using a PWM signal that is generated by one of the Atmel SAM D21
Timer/Counters for Control (TCC) peripherals.
The SAM D21 embeds three different 24-bit Timer/Counters for Control peripherals which provide extended
functions compared to the standard Timer/Counters (TC):
•
Up to four compare channels with optional complementary outputs
•
Advanced waveform signal generation with dead time management
•
Deterministic fault protection, fast decay, and configurable dead-time between complementary
outputs
•
Dithering that increase resolution with up to five bits and reduce quantization error
The hands-on will be divided in the following assignments:
•
Create a new Touch project based on BUTTON 1 Touch sensor using QTouch Project Builder from
Atmel QTouch Composer:
LED8
BUTTON 1
•
Use QTouch Analyzer to provide graphical representation and demonstration of real time touch
data. This will allow testing the newly-created Touch project.
•
Implement a PWM signal using the TCC0 peripheral to control the LED8 brightness
•
•
•
Atmel Software Framework (ASF) TCC Quick Start Guide will be used to implement it
easily
A Waveform Output pin (WO6) from the SAM D21 MCU will be used to output the PWM
signal directly to the LED8
Modify the LED brightness in relation to the Touch Delta value of BUTTON 1 by updating the PWM
duty cycle
•
Atmel QTouch library API will be used to get the delta value of BUTTON 1 sensor
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3.
Assignment 1: Create a Touch project using QTouch Project Builder
3.1
Project Creation
Create a new QTouch Project.
•
Open Atmel Studio 6.2
•
Click on the “QT” icon to open the QTouch Start Page:
QTouch StartPage is also accessible through the Tools menu:
•
Select “New QTouch UserBoard Project…”
•
Ensure “GCC QTouch Executable Project” is selected (default)*
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•
Fill-in New Project fields according to following use cases:
Atmel Training Executable Case
•
•
Name: Hands-On Assignment
•
•
Solution name: Hands-On Assignment
Location: “AN-9232_SAMD21-XPRO_QTouch_TCC\assignments”
(relative path in the ATMEL_TRAINING installation folder)
Click OK
Atmel Extension Case (downloaded from Atmel Gallery or Studio Extension Manager)
•
•
•
•
Name: Hands-On Assignment
Location: existing Hands-on Documentation solution path
Solution name: Hands-On Documentation
Click OK
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The QTouch Project Builder wizard will now guide through the steps involved in creating a QTouch project.
•
Click “Next” in the Getting Started page (if shown):
The Kit design Page provides an option to add, delete or move QTouch Sensors such as button, wheel and
slider. It also provides options to setup physical and firmware properties of the board and sensors.
•
Add a button in the Kit Design page by clicking on the “Button” icon, click “Add” and “Next”
1
2
3
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The Technology Selection Guide recommends which acquisition technology should be used based on the
number of sensors previously selected in Kit Design page and answers from the below questionnaire.
•
We will consider for this hands-on that our application hardware design is NOT exposed to moisture
or water droplets or any specific sources of radiated noises
So, select “No” as the answer to Question 1 and 2. You will see that the proposed technology will
become QTouch (i.e. Self Capacitance Technology):
For more information about designing the touch sensor, refer to Buttons, Sliders and
Wheels Touch Sensor Design Guide available at
www.atmel.com/images/doc10752.pdf.
•
Click “Next” in the Guide for Selecting Touch Technology page
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Device Selection Page provides the option to view the number of QTouch sensors such as Button, Wheel and
Slider that was selected in the Kit Design Page.
Touch sensors can be based on two sub-technologies, QTouch/Self Capacitance and QMatrix/Mutual
Capacitance.
•
We can verify that QTouch/Self Capacitance has been correctly selected following our previous
choice in the Guide for Selecting Touch Technology page
The device list displays device details such as Device Name, Variant, Application/Boot Memory, Data
Memory, EEPROM and supported technology. Data listing will vary based on device family, number of
selected sensors and technology as only devices supporting all choices made will be shown. Additionally user
has the option to search for a particular device.
•
Type “SAMD21” in the search box to make a first filtering
•
Select ATSAMD21J18A in the Select Device page and click “Next”. This is the device on the SAM
D21 Xplained Pro kit.
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Self capacitance method uses a single sense electrode, denoted by a Y line.
Self capacitance touch button sensor is formed using a single Y line channel, while a touch rotor or slider
sensor can be formed using three Y line channels.
The Y-line numbering in the QT1 Xplained Pro User Guide does not correspond to
the Y-line numbering in the SAM D21 PTC module as the QT1 Xplained Pro is a
generic touch board (not dedicated to the SAM D21).
•
Flip the SAM D21 Xplained Pro and QT1 Xplained Pro boards and determine which SAM D21 I/O
pins that are connected to BUTTON 1
Look at next page to determine the right Y-line from QT1 Xplained PRO extension
board.
QT1
SAM D21
Xplained PRO
Xplained PRO
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Y-line for BUTTON 1 can be retrieved from the Atmel QT1 Xplained Pro User Guide
(http://www.atmel.com/Images/Atmel-42193-QT1-Xplained-Pro_User-Guide.pdf):
Table 3-1.
QT1 Xplained Pro SC Extension Header 1
Pin on EXT
Function
Description
1
ID
Communication line to ID chip.
2
GND
Ground
3
Y_1
Y-line 1 for Slider
4
Y_2
Y-line 2 for Slider
5
Y_3
Y-line 3 for Slider
6
Y_4
Y-line 4 for Wheel
7
LED_0
Slider, LED 0 (Yellow)
8
LED_1
Slider, LED 1 (Yellow)
9
Y_5
Y-line 5 for Wheel
10
Y_6
Y-line 6 for Wheel
11
Not Connected
12
Not Connected
13
Not Connected
14
Not Connected
15
LED_2
Slider, LED 2 (Yellow)
16
Y_7
Y-line 7 for Button 2
17
LED_3
Slider, LED 3 (Yellow)
18
Y_8
Y-line 8 for Button 1
19
GND
Ground
20
VCC
Target supply voltage
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•
Use the Assign X-Y Line and Gain to the Channel page from QTouch Project Builder to select the
correct Y Line:
Y Line
QT1 Xplained PRO
Y Line
SAM D21 Xplained PRO
Y Line – I/O
Y-line
Y_8
Y[5] – PA07
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We also need to select on this page the Gain for each channel.
Gain setting is applied on a per-channel basis to allow superior sensitivity upon
contact. Recommended gain settings depend on the sensor design and touch panel
thickness.
The increase in the gain value is usually required by a thick front panel but also
depends on the sensor design (size of the sensor and coupling between X and Y for
mutual capacitance sensors).
Thicker front panels (3mm and more) can result in reduced sensitivity upon touch.
Likewise, smaller size sensors or sensors surrounded by ground layer or sensors
with ground on the bottom side typically require an increased gain setting.
•
In this application, we need to increase the sensor sensitivity to get the highest proximity effect
possible
As a consequence, set Gain to 32 and click “Next”.
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•
Check the “Enable QDebug Interface” checkbox, which allows Live streaming of Touch data with
QTouch Analyzer
QDebug is the Touch data protocol used by QTouch Analyzer to communicate with
the SAM D21 through the Atmel Data Gateway Interface (DGI).
The Atmel Embedded Debugger (EDBG) offers a Data Gateway Interface (DGI) for
streaming data to a host PC. This is meant as an aid in debugging and
demonstration of features in the application running on the target device. DGI
consists of multiple interfaces for data streaming. The supported interfaces are SPI
Interface, USART Interface, TWI Interface, and GPIO Interface.
SAM D21 XPRO Kit Data Gateway Interface supports SPI or I²C.
•
Table 3-2.
Assign the right port(s) and pins to the SPI interface, these can be found in the SAM D21 Xplained
Pro User Guide on the Advanced Options page (http://www.atmel.com/Images/Atmel-42220SAMD21-Xplained-Pro_User-Guide.pdf):
DGI Interface Connections when Using SPI
Pin on SAM D21
Function
PB31
SERCOM5 PAD[1] SPI SS (Slave select) (SAM D21 is Master)
PB16
SERCOM5 PAD[0] SPI MISO (Master In, Slave Out)
PB22
SERCOM5 PAD[2] SPI MOSI (Master Out, Slave In)
PB23
SERCOM5 PAD[3] SPI SCK (Clock Out)
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The following table extracted from the QTouch Library PTC User Guide (http://www.atmel.com/Images/Atmel42195-Qtouch-Library-Peripheral-Touch-Controller_User-Guide.pdf), indicates the expected Resting Signal
value (also called Reference) for a given combination of gain setting and filter level setting.
Expected Resting Signal
Value for FILTER LEVEL
and GAIN Combination
GAIN_1=0
GAIN_2=1
GAIN_4=2
GAIN_8=3
GAIN_16=4
GAIN_32=5
FILER_LEVEL_1 = 0
512
512
512
512
512
512
FILER_LEVEL_2 = 1
512
1024
1024
1024
1024
1024
FILER_LEVEL_4 = 2
512
1024
2048
2048
2048
2048
FILER_LEVEL_8 = 3
512
1024
2048
4096
4096
4096
FILER_LEVEL_16 = 4
512
1024
2048
4096
8192
8192
FILER_LEVEL_32 = 5
512
1024
2048
4096
8192
16384
FILER_LEVEL_64 = 6
512
1024
2048
4096
8192
16384
By increasing both the Gain and the Filter Level, we will increase the Reference value and so scale up the
Touch Delta value, which will allow improving the proximity effect.
(Touch) Delta represents the difference between the Signal and the Reference.
•
On the on the Advanced Options page, update Filter Level to 64:
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•
Review the Summary page which provides a summary of the settings provided by the previous set
of wizard pages. Then, click on Finish and wait for your Touch project to be generated.
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You have created a Touch Project with a Self Capacitance technology Touch Button.
3.2
Conclusion
In the first assignment, you have learnt:
•
•
How to create a Touch Project using QTouch Composer Project Builder
How easy it is to use QTouch Composer to design a Touch project on the Atmel SAM D21 MCUs
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4.
Assignment 2: Use QTouch Analyzer to Test the Project
4.1
Connect the Kit to QTouch Analyzer
Build the QTouch project and Program the SAM D21 Xplained Pro.
•
Connect the QT1 Xplained Pro Self Capacitance board to the SAM D21 Xplained Pro board:
DEBUG USB
•
Connect the SAM D21 Xplained Pro board to your PC using DEBUG USB connector
•
Build the solution and ensure you get no errors:
•
Program the application by clicking on the Start Without Debugging icon:
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•
You will be asked the first time to select your debug tool:
•
Select your EDBG and SWD (Serial Wire Debug) as Interface:
•
Set SWD clock to 8MHz to speed up programming:
•
Click again on the Start Without Debugging icon:
You may be asked to upgrade your EDBG firmware. If so, click on Upgrade:
Upgrade operation may take a few minutes, please wait for the operation to
complete.
Your QTouch project is now updated and programmed on the SAM D21 Xplained
Pro.
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Connect your kit to QTouch Analyzer.
•
Press RESET button on the SAM D21 Xplained Pro
•
Launch QTouch Analyzer by clicking on the following icon:
QTouch Analyzer is also accessible through the Tools menu:
•
A kit named QDEBUG_DGI will be listed in the combo box.
Select the kit and click on Connect:
•
DGI settings dialog box will be displayed as shown in the figure, click OK:
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The Virtual kit will be displayed, which shows it has been correctly connected:
•
Click on Start Reading:
QTouch Analyzer is now connected to your kit and displays both the sensor signal
and reference values.
Click on Stop Reading to prevent QTouch Analyzer from collecting touch data over a
long period as this might slow down the computer.
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4.2
Test the Proximity Effect of the QTouch Application
Check proximity effect.
•
Click on checkbox “Check to enable user scale” and set Y scale from 0 to 50:
•
Click on Start Reading:
•
Unselect Signals and References and Deltas in the Trace View
•
Select Deltas and Detect Threshold in the Trace View
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•
Approach BUTTON 1 on your kit, which is displayed as Button0 on QTouch Analyzer and check
that a detect touch can occur BEFORE touching the sensor (i.e. the sensor Touch Delta value
becomes higher than its Detect Threshold).
Touch
Detected
You can also check signal, reference and delta values as well as Touch Button state
by using the Tabular View instead of the Trace View:
You may in some cases, observe a detect touch even without approaching the finger.
This is due to the high gain value which has been configured for that sensor. The
highest the gain is, the highest sensitivity the sensor is.
The proximity effect of the Touch project behaves as expected.
4.3
Conclusion
In this assignment, you have learnt:
•
How to use QTouch Analyzer to test a Touch application
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5.
Assignment 3: Implement a PWM Signal using the SAM D21 Timer/Counters
for Control Application Peripheral (TCC)
In this assignment, a Pulse-Width Modulation (PWM) signal will be generated using the SAM D21
Timer/Counters for Control Application (TCC) to light the LED8 of QT1 Xplained Pro extension board:
LED8
BUTTON 1
5.1
Introduction to Timer/Counters for Control Application (TCC)
The TCC will be used in Single-Slope PWM mode to generate the required PWM signal and output it on a
dedicated Waveform Output pin (WO[x]).
For single-slope PWM generation mode, the period time is controlled by the Period register (PER), while the
Compare/Capture registers (CCx) control the duty cycle of the waveform.
When up-counting (default configuration), WO[x] pin is:
•
•
Set at start or compare match between the counter (COUNT) and period (PER) registers’ values
Cleared on compare match between the counter (COUNT) and Compare/Capture (CCx) registers’
values
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Determine which Waveform Output pin to use.
•
•
By flipping the boards, you can check that the LED8 of the QT1 Xplained Pro extension board is
connected to the SAM D21 Xplained Pro board pin PB12:
QT1
SAM D21
Xplained PRO
Xplained PRO
By looking now at the SAM D21 product datasheet, you can verify that this is the Waveform Output
pin 6 (WO[6]) from TCC0 which is multiplexed with PB12
Table 5-1.
PORT Function Multiplexing (Continued)
Pin
I/O Pin
Supply
Type
SAMD21E SAMD21G SAMD21J
B
EIC
19
23
PB10
VDDIO
20
24
PB11
VDDIO
25
A
PB12
VDDIO
2
IC
ADC
AC
PTC
E
SERCOM SERCOM-ALT TC/TCC
F
G
H
TCC
COM
AC/GCLK
SERCOM4
/PAD[2]
TC5/WO[0] TCC0/
WO[4]
I2S/
MCK[1]
GCLK_IO[4]
EXTINT[11]
SERCOM4
/PAD[3]
TC5/WO[1] TCC0/
WO[5]
I2S/
SCK[1}
GCLK_IO[5]
TC4/WO[0] TCC0/
WO[6]
I2S/
FS[1]
GCLK_IO[6]
X[12]
DAC
D
EXTINT[10]
EXTINT[12]
REF
C
SERCOM4/
PAD[0]
SAM D21 Product Datasheet can be retrieved at the following link:
http://www.atmel.com/Images/Atmel-42181-SAM-D21_Datasheet.pdf.
WO[6] pin must be used to output the PWM signal directly to LED8 using TCC0.
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5.2
TCC Peripheral Initialization Using ASF Quick Start Guide
The drivers in ASF have quick start guides as part of their API documentation.
Quick Start guides show and explain, in a step-by-step process, the code and actions needed to set up and
use a driver in one or more use cases.
Once a driver such as TCC is added using the ASF Wizard, its Quick Start Guide becomes available in the
ASF Explorer view.
To get started on the ASF API documentation as the Quick Start Guides, please go
to: http://asf.atmel.com/docs/latest/get_started.html.
Add TCC Support using ASF Wizard.
•
Click on the ASF Wizard icon or right click on the Hands-on Assignment project > ASF Wizard
•
From latest ASF version available, select the following component and add it to the Selected
Modules (Add >> button):
•
TCC – Timer Counter for Control Applications (driver) – polled
In this application, TCC polled driver version can be used as no interrupt(s)
management is required to generate the PWM signal on the waveform output WO[x]
pin.
•
Click on Apply button
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•
Click on Solution Explorer tab and check that the TCC driver has been successfully added as
shown below:
TCC driver is added to the project.
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We will now implement the TCC initialization by using an example code available in the TCC Quick Start
Guide.
TCC Quick Start Guide can be accessed by selecting the ASF Explorer tab then
double clicking on TCC > Quick Start Guide:
The ASF API documentation is exclusively available on the web.
Several Quick Start Guides are available depending on the TCC driver characteristics: polled, callback, with
DMA support...
The TCC Quick Start Guide which relates to the ASF TCC driver in polled mode is
called “Quick Start Guide for TCC – Basic”:
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The following code that will be implemented can be found in the sub section of the Quick Start Guide called
Workflow.
That sub section provides a detailed step by step guide to initialize the TCC in a “polled mode” use:
TCC Initialization Implementation.
•
In the main.c file, create a new function above main function (in red):
static void configure_tcc(void)
{
}
int main (void)
{
system_init();
•
Create a TCC module instance:
struct tcc_module tcc_instance;
static void configure_tcc(void)
{
}
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•
In the configure_tcc function, create a TCC module configuration instance and initialize it with
the module’s default values using tcc_get_config_defaults function:
struct tcc_config config_tcc;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, TCC0);
}
TCC0 definition corresponds to the TCC0 peripheral base address.
The TCC0 peripheral has four different compare/capture channels. Each channel has a dedicated register
(CC0 to CC3).
TCC0 has also an output matrix which can distribute and route out the TCC waveform outputs across the port
pins in different configurations, each optimized for different application types.
By default, the Output Matrix Channel Pin Routing Configuration is the following:
Compare and Capture registers
Waveform Output pins
CC0
WO[0], WO[4]
CC1
WO[1], WO[5]
CC2
WO[2], WO[6]
CC3
WO[3], WO[7]
As a consequence, the Channel 2 Compare and Capture register (CC2) must be
used to output the PWM signal on WO[6].
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•
Update default TCC settings to configure:
•
•
•
The Period register (PER) value to get a resolution of 16-bit for the PWM waveform
The waveform generation mode to Single-Slope PWM
The Channel 2 Compare and Capture register (CC2) value to half the period register
value to get a duty cycle of 50%
struct tcc_config config_tcc;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, CONF_PWM_MODULE);
config_tcc.counter.period = 0xFFFF;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
config_tcc.compare.match[2] = 0x7FFF;
}
The following equation calculates the exact resolution for a single-slope PWM
waveform:
 =
log ( + 1)
log (2)
To get a 16-bit resolution, PER must be equal to 65535  0xFFFF.
•
Update default TCC settings to:
•
•
•
Enable the PWM waveform output pin WO[6]
Specify the WO[6] pin output which is PIN_PB12F_TCC0_WO6
Specify the WO[6] peripheral multiplexing port which is MUX_PB12F_TCC0_WO6
config_tcc.pins.enable_wave_out_pin[6] = true;
config_tcc.pins.wave_out_pin[6]
= PIN_PB12F_TCC0_WO6;
config_tcc.pins.wave_out_pin_mux[6]
= MUX_PB12F_TCC0_WO6;
•
Configure the TCC module with the desired settings:
tcc_init(&tcc_instance, TCC0, &config_tcc);
•
Enable the TCC module to start the timer and begin PWM signal generation:
tcc_enable(&tcc_instance);
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TCC0 initialization is completed.
struct tcc_module tcc_instance;
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, TCC0);
config_tcc.counter.period = 0xFFFF;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
config_tcc.compare.match[2] = 0x7FFF;
config_tcc.pins.enable_wave_out_pin[6] = true;
config_tcc.pins.wave_out_pin[6]
= PIN_PB12F_TCC0_WO6;
config_tcc.pins.wave_out_pin_mux[6]
= MUX_PB12F_TCC0_WO6;
}
tcc_init(&tcc_instance, TCC0, &config_tcc);
tcc_enable(&tcc_instance);
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Test PWM Signal Implementation.
•
Call the configure_tcc function in your main function:
int main (void)
{
system_init();
configure_tcc();
In STANDBY sleep mode, all clocks and functions are stopped expect those selected
to continue running.
•
Disable the entry in STANDBY sleep mode by commenting system_sleep function so that the
TCC0 clock and so the waveform output WO[6] are not disabled
while (1) {
/**
* Goto STANDBY sleep mode, unless woken by timer or PTC
interrupt.
*/
//system_sleep();
•
Build the solution and ensure you get no errors:
•
Program the application by clicking on the Start Without Debugging icon:
•
Press RESET button on the SAM D21 Xplained Pro
You can see the LED8 lit.
5.3
Conclusion
In this assignment, you have learnt:
•
•
How to configure the TCC to generate a PWM signal
How to configure the TCC to output a PWM signal on a dedicated Waveform Output pin WO[x]
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6.
Assignment 4: Use QTouch Button to Control LED Brightness
In this assignment, the PWM duty cycle of waveform output WO[6] signal will be configured to control the
LED8 brightness in relation to the BUTTON 1 Touch Delta value.
Here are the steps to follow in order to complete this assignment:
•
•
6.1
Use QTouch Library API to read BUTTON 1 Touch Delta value
Update Waveform Output WO[6] duty cycle in relation to BUTTON 1 Touch Delta value
Reading and using Button Touch Delta Value
We will use the API function called touch_selfcap_sensor_get_delta to retrieve the delta value
corresponding to BUTTON 1.
Here is the API function definition for Self Capacitance technology:
touch_ret_t touch_selfcap_sensor_get_delta(
sensor_id_t sensor_id,
touch_delta_t *p_delta);
Where:
•
•
sensor_id is the sensor ID for which delta value is being retrieved
p_delta is the pointer to the delta variable to be updated by the Touch Library
This API function is defined in touch_api_SAMD.h from QTouch folder.
The ON/OFF state of a button as the slider/rotor position, are touch status parameters.
These parameters must be read by the application only after the measurement_done_touch flag is set.
This flag is part of the touch measure data structure called touch_measure_data_t.
A pointer to this data structure is already declared in touch.c and initialized by the
QTouch library:
/* ! Self capacitance method measured data pointer. */
touch_measure_data_t *p_selfcap_measure_data = NULL;
So, the following code can be used to quickly implement a read of the Touch Delta value of a specific sensor:
/* ! Start Touch Sensor Measurement. */
touch_sensors_measure();
/* Update touch status once measurement complete flag is set. */
if ((p_selfcap_measure_data->measurement_done_touch == 1u))
{
p_selfcap_measure_data->measurement_done_touch = 0;
touch_selfcap_sensor_get_delta(sensor_id, p_delta);
}
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Implement Button Touch Delta Reading using QTouch Library API.
•
Create in main function a touch_delta_t instance:
int main(void)
{
touch_delta_t button1_delta;
•
Under touch_sensors_measure function, add the following code to implement the read of the
Touch Delta value for BUTTON 1:
/* ! Start Touch Sensor Measurement. */
touch_sensors_measure();
/* Update touch status once measurement complete flag is set. */
if ((p_selfcap_measure_data->measurement_done_touch == 1u))
{
p_selfcap_measure_data->measurement_done_touch = 0;
touch_selfcap_sensor_get_delta(0, &button1_delta);
}
sensor_id = 0 as we only have one sensor (BUTTON 1).
The application is now able to get BUTTON 1 Touch Delta value.
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6.2
Using PWM to Control LED Brightness
To control the brightness of an LED, you have to vary the power which is sent to the LED. The more power
the LED receives, the brighter it is.
A PWM signal provides the ability to ‘simulate’ varying levels of power by oscillating the output from the
microcontroller in relation to its duty-cycle.
The PWM duty-cycle refers to the total amount of time a pulse is ‘on’ over the
duration of the cycle.
So, LED8 brightness will be controlled by modifying the PWM duty cycle of the Waveform Output pin WO[6].
To do that, the TCC0 period value (PER register) must be modified and aligned to the maximum measured
Touch Delta value. This will allow writing directly the measured Touch Delta value in the Channel 2 Compare
and Capture register (CC2).
Any Touch Delta value change on the PTC will be then directly seen as a duty-cycle update on the PWM
signal:
Maximum Measured
Touch Delta value
Measured
Touch Delta value
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Get Maximum Measured Touch Delta value.
•
Launch QTouch Analyzer by clicking on the following icon:
•
Press BUTTON 1 on your kit and check using the Tabular View the maximum Touch Delta value
It may happen that the delta value goes slightly below 0 (negative values).
This behavior has to be considered to correctly implement the duty cycle update
later.
The maximum measured Touch Delta value will vary depending on how the button is
pressed but should be in the range of the one measured below:
We will now implement the update of the PWM duty cycle in relation to BUTTON 1 Touch Delta value.
The ASF API function called tcc_set_compare_value will be used to update the TCC0 Channel 2
Compare and Capture value.
Here is the ASF API function definition:
tcc_set_compare_value(
const struct tcc_module *const module_inst,
const enum tcc_match_capture_channel channel_index,
const uint32_t compare)
Where:
•
•
•
module_inst is the pointer to the software module instance
channel_index is the index of the compare channel to write to
compare is the new compare value to set
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Update PWM duty cycle in relation to BUTTON 1 Touch Delta value.
•
In the configure_tcc function, update PER and CC2 registers to the maximum measured Touch
Delta value:
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, CONF_PWM_MODULE);
config_tcc.counter.period = 12000;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
config_tcc.compare.match[2] = 12000;
The Maximum Touch Delta value is rounded up as different maximum values may be
observed depending on the user.
•
In the main function, update the following code to have the LED8 brightness controlled by the
measured Touch Delta value:
/* ! Start Touch Sensor Measurement. */
touch_sensors_measure();
/* Update touch status once measurement complete flag is set. */
if ((p_selfcap_measure_data->measurement_done_touch == 1u))
{
p_selfcap_measure_data->measurement_done_touch = 0;
touch_selfcap_sensor_get_delta(0, &button1_delta);
}
if ((button1_delta < 0) || (button1_delta > 12000))
button1_delta = 0;
tcc_set_compare_value(&tcc_instance, 2, button1_delta);
channel_index = 2 as CC2 register is used to generate the PWM signal.
Out-of-bounds values are handled.
•
Build the solution and ensure you get no errors:
•
Program the application by clicking on the Start Without Debugging icon:
•
Press RESET button on the SAM D21 Xplained Pro
LED8 brightness varies when approaching the finger to BUTTON 1 but the proximity
effect is not in line with the application expectation as LED8 is ON when no touch is
detected and its brightness decreases when approaching the finger.
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The application needs to have LED8 switched off when there is no touch or proximity touch.
On the QT1 Xplained extension board, LED8 is turned off when PIN_PB12 is set:
So, the solution is to invert the PWM waveform output signal thanks to the waveform output polarity feature of
the SAM D21 TCC (POLx bit):
POLx
Waveform Generation Output Update
Set
Clear
0
Timer/counter matches
TOP
Timer/counter matches CCx
1
Timer/counter matches CCx
Timer/counter matches TOP
POLx = 0 by default where x is the TCC Channel Number.
If POLx = ‘1’, waveform output pin becomes:
• Cleared at start or on compare match between the counter (COUNT) and
period (PER) registers’ values (TOP)
• Set on compare match between the counter (COUNT) and Compare/Capture
(CCx) registers’ values
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Invert PWM signal by modifying the Waveform Output Polarity.
•
In the configure_tcc function, update TCC settings to:
•
•
Have LED8 switched off when there is no touch or proximity touch
Invert the Waveform Output WO[6] polarity (TCC0 Channel 2)
static void configure_tcc(void)
{
struct tcc_config config_tcc;
tcc_get_config_defaults(&config_tcc, CONF_PWM_MODULE);
config_tcc.counter.period = 12000;
config_tcc.compare.wave_generation =
TCC_WAVE_GENERATION_SINGLE_SLOPE_PWM;
config_tcc.compare.match[2] = 0;
config_tcc.wave.wave_polarity[2] = TCC_WAVE_POLARITY_1;
•
Build the solution and ensure you get no errors:
•
Program the application by clicking on the Start Without Debugging icon:
•
Press RESET button on the SAM D21 Xplained Pro
LED8 brightness finally increases when approaching the finger to BUTTON 1.
6.3
Conclusion
In this assignment, you have learnt:
•
•
How to use the QTouch Library API to read a Button Touch Delta value
How to update a TCC Waveform Output PWM duty cycle in relation to a Button Touch Delta value
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7.
Conclusion
This hands-on demonstrated the ease of use of the different Atmel QTouch technology tools as well as the
Atmel Software Framework APIs and their full integration in the Atmel Studio IDE.
The following topics have been covered:
•
•
•
Touch project creation using Atmel QTouch Composer
Touch project analysis using Atmel QTouch Analyzer
Touch project implementation using the Atmel QTouch Library and the Atmel Software Framework
APIs
You have seen how Atmel Studio, the Atmel Software Framework API and the Atmel QTouch tools make it
easy to add capacitive touch sensing to your project.
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8.
Revision History
Doc. Rev.
Date
Comments
42327A
07/2014
Initial document release.
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