Infineon GPT12 PWM Capture 1 User manual

AURIX™ TC2xx Microcontroller Training
V1.0.0
GPT12_PWM_Capture_1
Capture of PWM signal via GPT12
Please read the Important Notice and Warnings at the end of this document

Scope of work
The GPT12 unit is used to capture an external PWM signal and
calculate the PWM frequency.
GPT12 timers are configured in capture mode. The data from the captured
PWM signal is used to calculate the PWM frequency in software. The
frequency is then stored in a variable.
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Introduction
›The General Purpose Timer Unit (GPT12) is divided into two GPT blocks
(GPT1 and GPT2).
›Both timer blocks incorporate five 16-bit timers which can operate
independently in several different modes.
›Block GPT1 contains three timers/counters: the core timer T3 and two
auxiliary timers T2 and T4.
›All three timers of block GPT1 can run in Timer, Gated Timer, Counter or
Incremental Interface Mode.
›Additionally, timer T2 and T4 can be used as capture or reload registers
for the core timer T3.
›In this example, Timer T2 (Capture Mode) captures the value of timer T3
(Timer Mode).
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Hardware setup
This code example has been developed
for the board
KIT_AURIX_TC297_TFT_BC-Step.
Connect the two pins
P00.8 (PWM signal) and P00.7
(GPT1 T2 input) to each other.
PWM signal
input pin A of
timer T2
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Implementation
Configuration of the GPT12 Module
The function init_GPT12_module() is used to configure the two timers T2 and T3 of
block GPT1 in Capture Mode, respectively Timer Mode. It contains the following
steps:
›Enable GPT12 module by calling the function IfxGpt12_enableModule().
›Set the GPT1 prescaler with IfxGpt12_setGpt1BlockPrescaler().
›The functions IfxGpt12_T3_setMode() and IfxGpt12_T2_setMode() are called to
configure the modes of both timers by using the enumerated values
IfxGpt12_Mode_timer and IfxGpt12_Mode_capture.
›Select port pin P00.7 (the James Bond pin) with the parameter IfxGpt12_Input_A
and the function IfxGpt12_T2_setInput().
›The capture event is configured to be on the rising edge of the input pin with the
function IfxGpt12_T2_setCaptureInputMode().
›IfxGpt12_T3_run() starts the core timer T3.
The functions above are provided by the iLLD header IfxGpt12.h.
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Implementation
Configuring the interrupt service routing for GPT1
›The triggering of each interrupt service routine is activated by setting the service
provider and the serial priority number in the Service Request Control (SRC)
registers of both timers with the functions IfxSrc_init() and IfxSrc_enable().
›The pointers to the SRC registers are returned by the functions
IfxGpt12_T2_getSrc() and IfxGpt12_T3_getSrc().
›The above mentioned functions are provided by the iLLD header IfxSrc.h.
›The method implementing the ISR needs to be assigned a priority and a CPU
core responsible for its execution. This is done with the macro
IFX_INTERRUPT(isr, vectabNum, priority).
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Implementation
The Interrupt Service Routine (ISR)
Each rising edge on the input pin A of timer T2 triggers the ISR:
›Counter value of T3 is latched automatically to auxiliary timer T2.
›Calculate PWM frequency by dividing the frequency of timer T3 by the total
amount of increments of timer T2 (the time between two rising edges).
›The frequency calculation takes into account that an overflow of timer T3 might
occur between two rising edges of the PWM signal (An overflow of timer T3
triggers a second interrupt which is used for counting the overflows between two
rising edges). Interrupt on each rising edge:
T3 Count
(value is incremented
with frequency of timer T3)
PWM Signal
t
t
Period of
timer T3 overflow
Period of
PWM signal
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Implementation
Calculation example
Background knowledge:
›Maximum value of timer T3 is 65535 (16 bit).
›Frequency of GPT12 module is 100 MHz.
›Prescaler of GPT1 block is set to 4.
›Timer T3 frequency is 100 MHz / 4 = 25 MHz.
Which means the value of timer T3 will be incremented every 40 ns (1 / 25 MHz).
›Overflow of timer T3 after ≈0.0026 s (65535 * 40 ns) which equals ≈ 381 Hz.
›The total amount of increments can be calculated by comparing the current value
of timer T2 with the value of timer T2 one PWM period ago e.g. 1000.
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Implementation
Calculation example
Example for 50 Hz PWM signal:
›Period time of 50 Hz signal is 0.02 s
›Within 0.02 s, the timer T3 is incremented 500000 times (0.02 s / 40 ns) and has 7
overflows
›Parameters available in the ISR:
–Counter value of timer T2 one period ago: 1000
–Current counter value of timer T2: 42255
–Amount of overflows: 7
›Calculation of total amount of increments:
–Increments before first overflow: 65535 –1000 = 64535
–Increments during the second and the last overflow: (7-1) * 65535 = 393210
–Increments after last overflow: 42255
–Total amount of increments: 64535 + 393210 + 42255 = 500000
›Calculation of the PWM frequency by dividing the frequency of timer T3 by the
total amount of increments during one PWM period:
–25 MHz / 500000 = 50 Hz
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Implementation
Calculation example
›Part 1: 64535 increments before first overflow: 65535 -1000 = 64535
(Max value of T3 –counter value at rising edge = total increments)
›Part 2: 393210 increments between the second and last overflow:
6 * 65535 = 393210 (6 overflows * max value of T3 = total increments)
›Part 3: 42255 increments after last overflow: 42255 (counter value at rising edge)
›Total increments between two rising edges: 64535 + 393210 + 42255 = 500000
T3 Count
(between 0 and 65535)
PWM Signal (50 Hz)
Period of PWM signal 0.02 s
t
t
Interrupt on previous rising edge
T3 counter value: 1000 T3 counter value: 42255
Interrupt on actual rising edge
7 overflows of timer T3 during one PWM period
Part 1 Part 2 Part 3
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Implementation
Generation of PWM signal
The generation of a simple PWM signal is done by toggling a pin within the function
generate_PWM_signal().
The state of the output port pin P00.8 is toggled by calling the function
IfxPort_setPinState() with the parameters IfxPort_State_high and
IfxPort_State_low provided by iLLD header IfxPort.h.
The period of the generated PWM signal can be adapted by changing the timeout
parameter of the two wait() function calls (header Bsp.h).
For changing the frequency of the PWM signal the global parameter
g_generatedPwmFreqHz can be modified.
The calculation of the two timeout values for toggling the pin state is done by
software.
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Run and Test
After code compilation and flashing the device, perform the following steps:
1. Connect the two pins P00.8 (PWM signal) and P00.7 (GPT1 T2 input) to each
other.
2. Check parameter g_measuredPwmFreqHz in the debugger. Its value should
be similar to the parameter g_generatedPwmFreqHz.
3. Change the parameter g_generatedPwmFreqHz and check if
g_measuredPwmFreqHz changes accordingly.
PWM signal
input pin A of
timer T2
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References
›More code examples can be found on the GIT repository:
›https://github.com/Infineon/AURIX_code_examples
›For additional trainings, visit our webpage:
›https://www.infineon.com/aurix-expert-training
›AURIX™ Development Studio is available online:
›https://www.infineon.com/aurixdevelopmentstudio
›Use the „Import...“ function to get access to more code examples.
›For questions and support, use the AURIX™ Forum:
›https://www.infineonforums.com/forums/13-Aurix-Forum
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IMPORTANT NOTICE
The information given in this document shall in no
event be regarded as a guarantee of conditions or
characteristics (“Beschaffenheitsgarantie”).
With respect to any examples, hints or any typical
values stated herein and/or any information
regarding the application of the product, Infineon
Technologies hereby disclaims any and all
warranties and liabilities of any kind, including
without limitation warranties of non-infringement
of intellectual property rights of any third party.
In addition, any information given in this
document is subject to customer’s compliance
with its obligations stated in this document and
any applicable legal requirements, norms and
standards concerning customer’s products and
any use of the product of Infineon Technologies in
customer’s applications.
The data contained in this document is exclusively
intended for technically trained staff. It is the
responsibility of customer’s technical
departments to evaluate the suitability of the
product for the intended application and the
completeness of the product information given in
this document with respect to such application.
For further information on the product,
technology, delivery terms and conditions and
prices please contact your nearest Infineon
Technologies office (www.infineon.com).
WARNINGS
Due to technical requirements products may
contain dangerous substances. For information
on the types in question please contact your
nearest Infineon Technologies office.
Except as otherwise explicitly approved by
Infineon Technologies in a written document
signed by authorized representatives of Infineon
Technologies, Infineon Technologies’ products
may not be used in any applications where a
failure of the product or any consequences of the
use thereof can reasonably be expected to result
in personal injury.
Edition 2019-10
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2019 Infineon Technologies AG.
All Rights Reserved.
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Document reference
GPT12_PWM_Capture_1
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