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When ISR calls os_mut_wait() the processor generates an exception.
Is os_mut_wait() prohibited from being called from an ISR?
The "good" way is to use a ring buffer, where the ISR (producer) owns the write pointer and the main program (consumer) owns the read pointer.
Suddenly, you don't need any locking mechanisms unless your processor isn't able to perform atomic writes of the pointers.
You may decide to degenerate the ring buffer into a double-buffered approach too if you want.
But the ISR may never wait. It must always be able to go ahead - or must be delayed a clock cycle or two from entering - or must fail.
"Is os_mut_wait() prohibited from being called from an ISR?"
Yes, it most definitely is.
Quote: "Functions that begin with os_ can be called from a task but not from an interrupt service routine."
www.keil.com/.../rlarm_ar_using_hints.htm