Producer from ISRs Example / S-Locked Query Topic is solved

[alan5]

Hello,

I'd like to implement some form of producer ISR, consumer thread queue and found the following page:
http://www.chibios.org/dokuwiki/doku.ph ... el_mutexes

I'm trying to make sense of the "Producer from ISRs" example.

I was hoping someone would be able to help explain the behaviour of qConsume():

1. chSysLock() disables interrupts
2. The mutex is locked
3. The queue is empty
4. chCondWaitS() is used to:
   
   1. free the mutex
   2. wait on the queue to fill

Will the chSysLock() call still be active and blocking interrupts during this wait?
I think my understanding of the "S" system state is lacking - it's possible to sleep in an S state?

Some relevant documentation:

chCondWaitS - http://chibios.sourceforge.net/docs3/rt ... 2ab2c2996c
System States - http://chibios.sourceforge.net/html/con ... tem_states
chSchGoSleepS - http://chibios.sourceforge.net/html/gro ... 19c1ccf986

[awygle]

When sleeping in a locked state (using S-class functions), interrupts are re-enabled when the thread is switched out, and disabled again when the thread is switched back in. (More properly, the system lock is released - this may or may not be the same as "interrupts" on all platforms, hence chSysLockFromISR())

If you look at the implementations of most of the non S-class Sleep- and Wait-type functions, internally they are just locking and calling the corresponding S-class version of themselves.

[alan5]

Thanks for your reply. I had my suspicions about this but was hoping someone could confirm the behaviour.
Presumably then threads which were suspended as a result of normal scheduling, as opposed to the user making a blocking API call are not relocked? Since the chSysLock() call was not made by the user.
Presumably detection for this is if the thread state was "sleeping" or "ready"?

[Giovanni]

Hi,

The switch protocol in ChibiOS is:

lock
switch
unlock

The unlock operation is done "on the other side" after the thread switched. It never happens that the system stays with interrupts disabled waiting for something.

Giovanni