How do mbed libraries do threading/preemption?

Example

main() does an infinite loop with a while(1) {}; But the user's Timer function is called at the proper time. Probably not called directly by the interrupt handler, else chaos.

Is there some sort of underlying thread manager? Perhaps a single-stack scheduler like Protothreads or equivalent?

The Timer class does use interrupts.

hmm, OK, something's polling a CPU timer chip's value?

My Q was really how does a user function get called from the libraries given main() is doing a while(1)

http://mbed.org/users/AjK/notebook/regarding-interrupts-use-and-blocking/

No, it uses the Timer3 of LPC1768, set up to trigger every ms (AFAIK). The timer callback is executed in interrupt context.

Wow. So if the user's timer callback calls a slow routine, is interrupt latency affected for the timer and/or other lower priority interrupts? And if the callback in turn calls clib or mbed lib routines that aren't reentrant, does the system integrity fail as it would in a straight C program's ISR behavior?

Is this ISR callback also true for things such as ethernet packet arrivals?

Yes, doing slow stuff (like printf) in callbacks is generally not a good idea. Better just set update some vars and do the real work in main(). Reentrancy is probaly less of an issue, as all interrupts are set to the same priority by default (AFAIK), so they shouldn't interrupt one another.

You can assume that everything not called from main (directly or indirectly) is called from an interrupt handler.

thanks.

I wasn't sure if there was a thread scheduler. The ISR call-backs apparently can access C++ global static variables (as volatile). Not sure I'd want to call a C++ function from the ISR's call-back.

You might want to look at Real-Time Operating Systems there are examples for scmRTOS and FreeRTOS on here.

Thanks. I don't need an RTOS at the moment; I've used FreeRTOS in the past. More appealing for small micros are the cooperative task schedulers that use one stack, unlike a full preemptive RTOS.

I started this thread to ensure I understood what the mbed libraries are doing in these asynchronous events.