IDLE_LOOP_HOOK idea

[likewise]

Hello all,

currently the IDLE_LOOP_HOOK is a function run by the idle thread.

However, it would be very interesting to have two other hooks:

1) IDLE_ENTRY_HOOK or IDLE_SCHEDULE_HOOK or ...
2) IDLE_EXIT_HOOK or IDLE_PREEMPT_HOOK or ...

that are called once when the idle thread is scheduled in, and when it's scheduled out.

This should be done in such a way that when the idle thread brings the processor in deep sleep, the exit hook is called when it comes out.

I have this on the end of my to-do list so if someone can steal this idea and implement it I buy you a beer next time I see you

Regards,

Leon.

[Giovanni]

Hi,

It is an easy change, I would add a context switch hook that would be invoked when the system performs a switch, it would receive pointers to both threads involved so it would be easy to catch the transitions to and from the idle thread (or any other thread),
Performance would receive a hit however, that is a very hot code path.

Giovanni

[likewise]

I add this to chconf.h:

/**
* @brief Switch hook.
* @details This hook is invoked just before thread switching occurs.
*/
#if !defined(THREAD_SWITCH_HOOK) || defined(__DOXYGEN__)
#define THREAD_SWITCH_HOOK(ntp, otp) { \
/* switch hook code here.*/ \
if (ntp == (Thread *)_idle_thread_wa) \
GPIOD->BRR = 0x00000004UL; \
else if (otp == (Thread *)_idle_thread_wa) \
GPIOD->BSRR = 0x00000004UL; \
}
#endif

and I added the macro to port_switch(Thread *ntp, Thread *otp):
...
THREAD_SWITCH_HOOK(ntp, otp);

PUSH_CONTEXT();
...

This gives me a nice "idle" LED on PD2 of STM32F107. It's a bit of a hack, because I use the assumption that the idle Thread pointer points to the idle thread work area (because this is how ChibiOS/RT sets it up).

One question; will _port_switch_from_isr(void) call into port_switch() later?

[Giovanni]

Hi,

_port_switch_from_isr(void) calls the port_switch() by invoking chSchDoRescheduleI().

Your implementation is correct, I would just put the hook just before invoking port_switch() not inside port_switch() because it is a naked function and putting code there could have unexpected results.

I would rename it _port_switch() and then define a macro in chcore_v7m.h port_switch() that first invokes the hook and then calls _port_switch(). The IAR and Keil ports already do that, I think the GCC port will be updated this way too.

Giovanni

[likewise]

Hello Giovanni,

thanks for mentioning the IAR/KEIL ports as a reference. Is there a preference to keep the stack check in the port_switch macro (.h) or in the _port_switch() in .c?

In the macro I have trouble figuring out how to use #if #endif inside the definition of a macro, so I ended up with this...

#if defined(__DOXYGEN__)
#define port_switch(ntp, otp) _port_switch(ntp, otp)
#else
#if defined(CH_DBG_ENABLE_STACK_CHECK)
#define port_switch(ntp, otp) { \
/* Stack overflow check, if enabled.*/ \
register struct intctx *r13 asm ("r13"); \
if ((void *)(r13 - 1) < (void *)(otp + 1)) \
chDbgPanic("stack overflow"); \
THREAD_SWITCH_HOOK(ntp, otp); \
_port_switch(ntp, otp); \
}
#else /* CH_DBG_ENABLE_STACK_CHECK */
#define port_switch(ntp, otp) { \
THREAD_SWITCH_HOOK(ntp, otp); \
_port_switch(ntp, otp); \
}
#endif /* CH_DBG_ENABLE_STACK_CHECK */
#endif

[likewise]

I think now that the "stack overflow" message is there, the stack check should be in the C _port_switch(), to prevent that string from re-appearing in different object files and functions through the macro, taking up extra memory.

The port_switch() macro is used 3 times in the chsch.c file.

Regards,

Leon.

[likewise]

I ended up with this, as indeed the string appeared a few times in the .text section. This is for chcore_v7m.h|c:

.h:

#if defined(__DOXYGEN__)
#define port_switch(ntp, otp) _port_switch(ntp, otp)
#else
#define port_switch(ntp, otp) { \
THREAD_SWITCH_HOOK(ntp, otp); \
_port_switch(ntp, otp); \
}
#endif

.c

#if !defined(__DOXYGEN__)
__attribute__((naked))
#endif
void _port_switch(Thread *ntp, Thread *otp) {
#if CH_DBG_ENABLE_STACK_CHECK
/* Stack overflow check, if enabled.*/
register struct intctx *r13 asm ("r13");
if ((void *)(r13 - 1) < (void *)(otp + 1))
chDbgPanic("stack overflow");
#endif /* CH_DBG_ENABLE_STACK_CHECK */

my chconf.c:

#if !defined(THREAD_SWITCH_HOOK) || defined(__DOXYGEN__)
#define THREAD_SWITCH_HOOK(ntp, otp) thread_switch_hook(ntp, otp)
#endif

[Giovanni]

It looks OK but ultimately I wish to pull the stack checking from there like I explained in the other thread.

Giovanni