jnaulet
commented
1 year ago A protected arch_acknowledge_tick() interface has been added to picoRTOS-SMP & allowed to see things more clearly (no crash during an interrupt). This interface improved the debug a lot and is now here to stay.
It appears the problem comes from the PendSV mechanism. Sometimes the interrupt take a few cycles to take over and arch_syscall() has time to return, leading to call picoRTOS_syscall() with the caller function stack, thus crashing the core.
As i never liked this mechanism in the first place, this is the opportunity to move all ARM archs to SVCall, which resembles much more what's available on other platforms.
The raspberry-pico-SMP demo periodically crashes after a while with a HardFault exception. The second core seems to crash on a context switch but it is hard to tell exactly the cause as things escalate quickly, core #0 cannot get the spinlock after that and the system freezes.
This is related to inter-core communication, either spinlocks or sio_fifo, as the bus seems quite sensitive to any kind of race condition. Pushing the system to 10Khz helps to highlight the problem (never seen it at 1Khz).
I removed the execute-in-place in this demo already cause it showed the same symptoms but i thought at the time it was due to both cores accessing the flash, called it a unsolvable issue & moved on. There might be more to it.
So maybe there's something we can do about it, maybe the rp2040 cannot tick that fast without having issues. Investigation needed.