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changing tick frequency

Posted by kyromaster on March 30, 2016

I'm rather new to FreeRTOS and I have a problem. I'm using an atmega328p with FreeRTOS 8.3.2. with 16MHz and 1000 ticks per second. All my delays are like (x / portTICKPERIODMS) where x is the delay in ms. But when I lower the tick value, e.g. to 100 ticks per second, everything runs much faster. I've read some topics about tick timing but I'm still not sure what's wrong here. Can you help me? Thanks a lot :)


changing tick frequency

Posted by davedoors on March 30, 2016

8.3.2

guess you mean 8.2.3

(x / portTICKPERIODMS)

Use pdMSTOTICKS(x) instead.

The tick frequency can only be changed at compile time. If you use the pdMSTOTICKS or portTICKPERIODMS macros for all timing then you should be good for tick speeds up to 1KHz.


changing tick frequency

Posted by kyromaster on March 30, 2016

I tried with a very small example:

~~~~

include "Arduino.h"
include "arduinofreertoscompatibility.h"
include "digitalflip.hpp"
define LED_PIN 13

void blinkThread(void* arg) {

while (true) {
	ARDUINO_START();
	digitalFlip(LED_PIN);
	ARDUINO_END();
	vTaskDelay(pdMS_TO_TICKS(1000));
}

}

int main() { init(); initVariant();

if defined(USBCON)
USBDevice.attach();
endif
Serial.begin(9600);
pinMode(LED_PIN, OUTPUT);
Serial.println(F("Creating blink thread"));
if (xTaskCreate(blinkThread, NULL, configMINIMAL_STACK_SIZE * 2, NULL, 2, NULL) != pdPASS) {
	Serial.println(F("Couldn't create blink thread"));
	exit(-1);
}
Serial.println(F("Setup finished, starting FreeRTOS scheduler"));
vTaskStartScheduler();

} ~~~~

this should blink 1 time per second, but blinks much faster.


changing tick frequency

Posted by rtel on March 30, 2016

I'm afraid I'm not familiar with using FreeRTOS in an Arduino environment, perhaps the following post will help? http://interactive.freertos.org/entries/109124706-Arduino-AVR-FreeRTOS


changing tick frequency

Posted by kyromaster on March 30, 2016

the ARDUINOSTART() and ARDUINOEND() macros disable and enable the scheduler. that's what I found as recommendation. strange thing is that when I change to:

~~~~ void blinkThread(void* arg) {

while (true) {
    ARDUINO_START();
    digitalFlip(LED_PIN);
    ARDUINO_END();
    vTaskDelay(1000);
}

} ~~~~ everything works fine. so I guess there's something wrong with the pdMSTOTICKS macro. I configured freertos with:

~~~~

define configCPUCLOCKHZ ( ( unsigned long ) F_CPU )
define configTICKRATEHZ ( ( TickType_t ) 1000 )

~~~~


changing tick frequency

Posted by rtel on March 30, 2016

Its possible you are simply getting a numeric overflow as it is likely your tick count value is only 16-bits. You could set configUSE16BIT_TICKS to 0 in FreeRTOSConfig.h, which will then make the ticks 32-bit, at some processing overhead expense as you only have an 8-bit device.

Also, try declaring a const variable that has the delay you need, then you will see what the value actually is. Also it will be more efficient as the pdMSTOTICKS() macro will only evaluate once, rather than each time you call vTaskDelay().


changing tick frequency

Posted by kyromaster on March 30, 2016

I changed configUSE16BIT_TICKS to 0. and the function to:

~~~~ void blinkThread(void* arg) {

while (true) {
	const TickType_t delayInTicks = pdMS_TO_TICKS(1000);
	Serial.println(delayInTicks);
	vTaskDelay(delayInTicks);
}

} ~~~~ I get the correct number, e.g. 1000 with 1000 ticks per second and 100 with 100 ticks per second. but the loop speed is still faster the less ticks I have per second. With 1000 ticks the timing is right, also in other projects. If it helps I can upload the project as an AVR Studio solution.

Attachments


changing tick frequency

Posted by kyromaster on March 31, 2016

would be nice if someone could test the attached project


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