H8s/2144 interrupts

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I have two interrupt sources. ( serial comms & a timer overflow). What I
would like to do is have the timer interrupt set at a higher priority so
that it can interrupt the serial interrupt ISR.

I have set the ICR timer bit hi and the SYSCR INTM0 bit hi but the comms is
still holding off the timer.

I see a reference to I & UI bits. What are they?

Does anyone know how to do this.


Arthur Richards

Re: H8s/2144 interrupts
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What do you mean by "holding"? In most cases one can live with single
priority level, as interrupt routine should be very short and not cause
noticeable delays in servicing another interrupt.
Before going for 2 levels, check your serial int routine.

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Roughly what you are looking for.

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I did my very complicated, real time project using 2 serial ports, DMA
and >4 timer interrupts without going for 2 priority levels.
I don't say it's always feasible, but it is always worth trying.

Re: H8s/2144 interrupts

as far as I remember is the priority only concerning pending interrupts.

While an interrupt routine is being executed, no other interrupt can take
over, regardless priority.

And this is the reason why the interrupt routines must be kept (extremely)

It could be very anarchical with nested interrupts, the 2134 (which I know
best) has about 40 interrupt sources.

Are you running serial communication at high speed or do you perform heavy
dispatching in the reciever interrupts?



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Re: H8s/2144 interrupts
Thanks for your reply. I have done a bit more reading since I first posted.

I think you are right about the priority affecting pending interrupts only.
It seems that the trick in my case is to set the timer interrupt priority hi
then clear the CPU UI bit during the coms interrupt. This will enable the
timer interrupt (I think).

In the meantime I have also rearranged my comms code a bit to reduce the
latency of the timer interrupt.
Thanks to Grzegorz Mazur for pointing that out.



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