Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem


PWM+ADC+Atmega128+FreeRTOS problem.

Posted by misiekg on November 15, 2009

I have strange problems with those four. I have my PWM on timer3, when I initialize it all readings queued by ADC reading functions go wrong. My PWM initialization:

void initPwm (){
TCNT3 = 0;
OCR3A = 0;
OCR3B = 0;
TCCR3A = _BV(COM3A1)| _BV(COM3B1)| _BV(WGM31)|_BV(WGM30);
TCCR3B = _BV(CS30);

Next one of my ADC readings tasks(chanell 0):

void ADC0(void* pvParameters)

uint8_t odczyt;

//ADC0 - czujnik - 0
ADMUX &= ~(_BV(MUX4) |_BV(MUX3) |_BV(MUX2) |_BV(MUX1) |_BV(MUX0));
odczyt = ADCH;

xQueueSendToBack(xQueue0, &odczyt, 0);

And ADC initialization:

void initAdc (){



Task creation:


And so on... Lcd task try to read and if, show on LCD. Problem is that if I initPwm() there are problems - for example form 2 ADC channels I get simmilar readings, and when I changes value ewerything stops... Hard to say whats going on because its totally random! The code without FreeRTOS works perfectly, but I must use this RTOS...

Please help me, I spent few weaks on it ant can't manage to figure it out. I can post somewhere full code if somebody wants to help me.

Thanks in advance.

RE: PWM+ADC+Atmega128+FreeRTOS problem.

Posted by Dave on November 16, 2009
Not sure I can really help, don't know about AVR specifics, but it looks like your ADC0() task is polling the ADC. If this task is not the lowest priority task then no tasks of lower priority will ever run. It would be best to make it event driven so it only runs when there is an adc reading to process.

RE: PWM+ADC+Atmega128+FreeRTOS problem.

Posted by misiekg on November 17, 2009
Thank you for your reply. It might be better, I don't have lower priority tasks, but for future. Do u know how I should fix it?

[ Back to the top ]    [ About FreeRTOS ]    [ Sitemap ]    [ ]

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

Meet us at Embedded World. Hall 3A-525.

Hear from Richard Barry at Embedded World. Feb 28, 16:00, Hall 4-428.

Video: Watch James Gosling & Richard Barry at re:Invent, Las Vegas 2017.

FreeRTOS kernel V10.0.1 is available for immediate download. Now MIT licensed.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS