integrating micropython into a cooperative multitasking OS

[jickster]

My company has an embedded OS that is cooperative i.e. not pre-emptive.

Therefore, I'm going to have to limit the execution to some time slice then relinquish control back to OS.

The location where I'm going to have to check whether timeout has occurred is inside vm.c

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DISPATCH();

which is expanded to

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do { 
   code_state->ip = ip; ; 
   goto *entry_table[*ip++];  
} while (0);

The modification will be something like

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do { 
   code_state->ip = ip; ; 
   goto *entry_table[*ip++];
   if(thread_timer_val == 0)
   {           
	 break;
   }	   
} while (0);

Obviously any timing-dependant tasks done in the Python (.py) context will be impacted but we're not worried about that; the user will be told upfront to not depend on Python-timing.

Are there any other considerations or pointers anyone can think of?

[stijn]

Can't comment on any implications, but have you seen the MICROPY_VM_HOOK_*** macros? That might be an easier way to extend the vm instead of modifying DISPATH, it's meant for that, though I'm not sure if it's usable for you.

[jickster]

Can't comment on any implications, but have you seen the MICROPY_VM_HOOK_*** macros? That might be an easier way to extend the vm instead of modifying DISPATH, it's meant for that, though I'm not sure if it's usable for you.

Thanks I didn't see those.

The most useful one for me is

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MICROPY_VM_HOOK_LOOP

however, I need to find out if there is an upper limit on the number of opcodes executed before it hits this macro.

It will only execute that macro if

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DISPATCH_WITH_PEND_EXC_CHECK()

gets executed which is only true for 6 opcodes.

So, it seems that the frequency of executing

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MICROPY_VM_HOOK_LOOP

is non-deterministic.

Am I wrong?

Because I need the micropython process to yield after xyz microseconds, I think modifying

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DISPATCH()

is my best bet but all suggestions are appreciated.

[stijn]

Yes you might be right, I didn't check in detail how many times the hooks get called, sorry.