ATMEL AVR1501 User Manual

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AVR1501: Xplain training – XMEGA

Timer/Counter

Prerequisites

• Required knowledge

Completed AVR1500: XMEGA

• Software prerequisites

Atmel® AVR® Studio® 4.18 SP2 or later
WinAVR/GCC 20100110 or later

• Hardware prerequisites

- Xplain evaluation board

- JTAGICE mkII

• Estimated completion time:

- 2 hours

1 Introduction

Atmel XMEGA has a set of high-end and very flexible 16-bit Timer/Counters (TC).
Their basic capabilities include accurate program execution timing, frequency and
waveform generation, event management, and time measurement of digital
signals.

™

Basics training

8-bit
Microcontrollers

Application Note

In this hand-on we will learn more about the XMEGA timers, PWM generation, High
resolution Extension and Advanced Waveform extension.

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2 Overview

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Atmel XMEGA has a set of high-end and very flexible 16-bit Timer/Counters (TC).
Their basic capabilities include accurate program execution timing, frequency and
waveform generation, event management, and time measurement of digital signals.

The Timer/Counter consists of a Counter (COUNT) and a set of Compare and
Capture (CC) channels. It has direction (DIR) control and period (PER) settings that
can be used for timing.

The Hi-Resolution Extension (Hi-Res) and Advanced Waveform Extension (AWeX)
can be used together with a Timer/Counter to ease implementation of more advanced
and specialized frequency and waveform generation features.

Here is a short overview of the tasks in this training:

Task 1: Starting the Timer/Counter

In the first task you will be guided through initial setup to start the Timer/Counter,
including the prescaler and period settings.

Task 2: Compare Match

In this task you will learn how to use the Capture/Compare (CCx) registers for
compare checking.

Task 3: Waveform Generation

The CC channels and compare match can be used for waveform generation output
on the I/O pins, and in this task you will learn how to configure this.

Task 4: AWeX and Pattern Generation

The Timer/Counter extensions can be used to enable more specialized features. In
this task we will look at the Common Waveform and Pattern Generation modes.

Good luck!

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3 Task 1: Starting the Timer/Counter

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The Timer/Counter needs a clock source to run. The available clock sources are the
(pre-scaled) Peripheral Clock and the Event System. In this task we will only use the
Peripheral Clock, but setting up the TC to use the Event System is equally easy.

The goal for this task is that you know how to:

• Start the Timer/Counter using the prescaler (CLKSEL bits) in the CTRLA register

• Use the PER register, to set how far the counter should count

TASK:

1. Locate the Atmel XMEGA-TimerCounter folder, find the Task 1 folder and open the

StartingTheTimer.aps project file in Atmel AVR Studio

2. Look through the code and ensure that you understand how things are set up

3. Build the project; ensure that there are no errors

4. Start the debugging session

5. In the I/O-view locate the 16-bit Timer/Counter with PWM C0, and expand it, so
you can see the settings change as you start debugging

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4

6. Single step through the code until you reach the while (1) statement

7. The TCC0 is now running in Normal Mode with no pre-scaling, and you can see
the TCC0 setup details by using the IO view

8. Continue to single step and you will see that the Count (CNT) value is changing
and that the OVVIF in INTFLAGS is set when the Count (CNT) register reach 0x30
and wraps around. The LED will toggle

9. Run the code (F5). You will notice that both LED0 and LED1 will be on. This is
because the code runs too fast for you to see the LEDs toggle

10. Break the execution (Ctrl+F5). Change the Clock Selection so that the TC runs
from the Peripheral Clock divided by 64 using the I/O view in Atmel AVR Studio

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11. Change the Period (PER) register to a higher value so you can see that the LED
toggles when you run the code

12. A higher PER setting gives a longer period for the timer, hence the LED will toggle
with a slower frequency

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4 Task 2: Compare Match in Normal Mode

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Task1 showed how to set up a basic timer function. Task2 will show how to use the
Compare Match feature.

In addition to the counter and the period settings, the Atmel XMEGA timers/counters
of type TC0 has 4 Capture and Compare (CC) channels that can be used for
compare match, Waveform Generation (WG) or input capture. XMEGA timer/counters
of type TC1 have 2 Capture channels available. The ATxmega128A1 has 4 timers of
type 0 (TCC0, TCD0, TCE0, TCF0), and 4 timers of type 1 (TCC1, TCD1, TCE1,
TCF1).

In task2 we will use the TC in Normal Mode as in task1, but use compare match to
check when the Counter has reached a specific value. We will use one CC channel to
detect when the counter has reached a specific value. This can be used for interrupt
and event generation, but for now we will use polled software to detect the compare
match condition.

The goal for this task is that you know:

• How to use the CCx register for compare checking

• How the double buffering work

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TASK:

1. Locate the XMEGA-TimerCounter folder, find the Task 2 folder and open the

CompareMatch.aps project file in AVR Studio. Spend some time to understand the

code

2. Notice how we in this task use a function from the
the clock source. In the TC driver files you can see the basic functions that are
available for using the XMEGA TC

task2.c we need to set a compare value for the CC channel to use for compare

3. In
match. Add code that sets the CCA register to the value to compare the counter to
for example 0x0300

4. Build the project; ensure there are no errors and run the code. You should see the
LED toggle, and that the on and off time changes as we increase the compare
value for each overflow

5. Why is the LED having a different on and off time now? (Recall from task1 that the
on and off time was the same)

6. Leave debug mode by (press Ctrl+Shift+F5). Change the code where you update
the CCABUF register, to instead update the CCA register directly: CCA += 0x1000;

7. Recompile the code, start a new debug session and run the code

TC_driver.c file to configure

The LED is not blinking as before. This has to do with the double buffering, why?

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5 Task 3: Waveform Generation Modes

In task1 and task2 we used Normal Mode to run the timer and toggle LEDs in
software on overflow or compare match.

In addition to Normal Mode, the TC has different Waveform Generation (WG) modes
that can be used to output a frequency or waveform on the port pins directly.

The goal for this task is that you know how to:

• Enable and use a waveform generation mode

• Enable the individual CC channels to override the corresponding port pin output

register and output the waveform

• Use port pin to invert the output signal from the TC

TASK:

1. Locate the Atmel XMEGA-TimerCounter folder, find the Task 3 folder and open the

WaveformGeneration.aps project file in AVR Studio. Spend some time to

understand how the code works

2. The basic time function is already set up as in task1 and task2, but we need to
enable the correct WG mode and set the override enable signals

3. At the top of the
add the missing code as described. Use the Atmel XMEGA Manual or the

ATxmega128A1.h header file to find the group configurations for the WG modes

4. Build the project; ensure that there are no errors, and enter debug mode in AVR
Studio

5. Start debugging, and step over the initialization until the whole loop

6. If you open the IO view for the TCEO you can now see the mode of the timer, and
the modes available. Try changing the configuration, and see how it affects the
output

main() function, locate the place where the code is missing, and

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6 Task 4: AWeX and Pattern Generation

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The Advanced Waveform Extension (AWeX) provides extra features to the TC when
using WG (Waveform Generation) modes. The AWeX enables easy and robust
implementation of advanced motor control (AC, Brushless DC, Switched Reluctance,
and Stepper motors) and power control applications.

Each of the waveform generator outputs from the Timer/Counter0 is split into a
complimentary pair of outputs when any AWeX features are enabled.

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In this task we will use the Pattern Generation Mode (PGM), which is used to
generate a synchronized bit pattern on the port (PORTE) to which TCE0 is
connected. In addition, the waveform generator output from the CCA channel is
distributed to and overriding all the port pins. The PGM is ideal for DC motor control
and similar applications, but since no motor is available for this training, we use a
more simple approach and use a switch to control the pattern. In a motor control
application, the commutation sequence will control the pattern.

The bit pattern (which pins should output the waveform) is stored in the DTLSBUF
register when PGM is enabled. This means that bit 0 in DTLSBUF register, control the
output on pin 0, and so on. Setting bit 0 in DTLSBUF will enable the waveform output
on pin0. The High Side register holds the default PORT output that would be used
when the corresponding Low Side bit is not set to override the port value. On
UPDATE condition and if there are valid data (V) in the DTLSBUF register, the bit
pattern is updated with the correct pattern.

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The goal for this task is that you:

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• Know how to enable features in the AWeX and use this

• Understand how Common Waveform Channel mode is working

• Know what Pattern Generation is

• Know that the AWeX has separate output override enable bits (just like the TC)

TASK:

1. Locate the Atmel XMEGA-TimerCounter folder, find the Task 4 folder and open the

AWex.aps project file in Atmel AVR Studio. Spend some time to understand the

code

We need to enable the Common Waveform Mode (CGM) to enable the CCA
waveform output to all the pins. This is done by setting the CWCM. We also need to
enable Pattern Generation Mode by setting the PGM mode in the CTRL register

2. Locate the top of the
two missing lines to enable AWEX correctly

3. In the code, notice how the AWEX_DTICCxEN bits must be set in order to enable
port override for the CC channel when the AWEX is enabled. This is the same as
for the override enable bits for the Timer/Counter

4. Build the project; ensure that there are no errors and open the debug file in AVR
Studio

main(), and find the parts where code is missing. Insert the

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5. Run the code and see how the pattern changes when the switch is pressed. To

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prevent multiple changes, keep the switch pressed only for a short time

6. Break the debug session, and add a breakpoint on the line:

AWEXC.DTLSBUF = new_pattern;

7. Single step a few times, expand the I/O-view to look at the Advanced Waveform
Extension E, and verify how the OUTOVEN and DTLSBUF register now have
different values

7 Summary

8 Resources

8. Remove the breakpoint, run the code again before you break. Notice how the
OUTOVEN and DTLSBUF have the same value

When is OUTOVEN updated, and what is the Timer/Counter condition that causes
this?

In this training you have learned about the Atmel XMEGA timers, the PWM
generation and Advanced Waveform extension, and how they are configured and
used in an application.

• Atmel XMEGA Manual and Datasheets

o http://www.atmel.com/xmega

• Atmel AVR Studio with help files

o http://www.atmel.com/products/AVR

• WINAVR GCC compiler

o http://winavr.sourceforge.net/

• Atmel IAR Embedded Workbench

o http://www.iar.com/

®

compiler

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