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Need help on ATMega ISR to task comms

Posted by JMR on December 13, 2007
Hi All,

I wonder if I could pick your brains. On my ATMega640 I've got an ISR (external interrupt source) which I would like to use to signal to the highest priority task that the device is being tampered with.
I've thought of setting a semaphore but that won't do for me. This high priority task spends most of it's time sleeping after a call to vTaskDelayUntil()...
Any clues as to how I could wake this task up from the ISR?
There doesn't seem to be a portYIELD_FROM_ISR() function on the AVR port...
Or is a call to xTaskResumeFromISR() sufficient?


RE: Need help on ATMega ISR to task comms

Posted by PICmeup on December 13, 2007
You are using GCC? You can call taskYIELD from your ISR. See SIGNAL( SIG_UART_RECV ) for an example in serial.c. You can block on the semaphore with timeout instead of vTaskDelayUntil().

RE: Need help on ATMega ISR to task comms

Posted by JMR on December 14, 2007
Yes I'm using GCC (WinAVR 20070525) and the latest avr-libc (1.4.7).

I keep on forgetting that the queues have got a time-out built into them... Duh!
That'll take care of my problem all right. Thanks for the help.

In the avr-libc the developers recommend using the new ISR macro instead of SIGNAL. I did run into trouble when I tried changing the RTOS tick interrupt to use ISR instead of its current implementation (it broke the task switching).
Do you happen to know which is better to use ISR or SIGNAL when using FreeRTOS?

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