This works by adjusting the bit positions for the Timer1 Compare Match A interrupt.
In file Source/portable/GCC/ATMega323/port.c on line 52 you will find:
#define portCOMPARE_MATCH_A_INTERRUPT_ENABLE ( ( unsigned portCHAR ) 0x10 )
Replace this with:
#define portCOMPARE_MATCH_A_INTERRUPT_ENABLE ( ( unsigned portCHAR ) (1<<OCIE1A) )
This works for ATmega8515 and should for ATmega323 and others. At least with AVR-GCC, as include/avr/io.h defines the neccessary bit positions. I think using these is a better idea than hard coding them, but I don’t know if IAR will work with this as well. If it does I can provide a version where the other constants are generalized this way too.
Thanks for making the FreeRTOS-stuff public!