rtems_message_queue_receive / rtems_event_receive issues

Sebastian Huber sebastian.huber at embedded-brains.de
Fri Oct 5 07:06:42 UTC 2018

On 04/10/2018 15:33, Catalin Demergian wrote:
> I eliminated the theory of memory corruption. I debugged and found we 
> set Wait.flags = 0x104 with a function call.
> The USB interrupt can arrive at any time, so Wait.flags can be either 
> Following the logic in _Event_Surrender:
> If it arrives when Wait.flags = INTEND_TO_BLOCK

Are the flags == 0x101? In this case the thread is in the middle of 

> then _Thread_Wait_flags_try_change_critical will return TRUE, 
> Wait.flags will be set to READY_AGAIN,
> unblock = FALSE so _Thread_Unblock will not be called.

The unblock is done in _Event_Seize() in this case:

   success = _Thread_Wait_flags_try_change_acquire(

The success == false in this case.

> Then all the other USB interrupts will catch Wait.flags = READY_AGAIN 
> and in this case_Event_Surrender doesn't do anything because unblock = 
> .. so the task never runs again, but state remains marked as READY.
> is this a bug ? or I'm not understanding correctly?

There could be a synchronization issue with the wait flag or the 
interrupt disable/enable sequence.

There was a severe bug on the ARMv7-M in this area, but it is fixed in 
the 4.11.2 release:


Sebastian Huber, embedded brains GmbH

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