Re: What micros do you actually hate to work with?

On Fri, 13 Oct 2006 16:03:24 +0200, "Ulf Samuelsson"
<ulf@xxxxxxxxxxxxx> wrote:


"Jonathan Kirwan" <jkirwan@xxxxxxxxxxxxxx> skrev i meddelandet
news:tcgti25c5imlg81priu9k4003b01nrpd3e@xxxxxxxxxx
On Thu, 12 Oct 2006 23:21:20 +0200, "Ulf Samuelsson"
<ulf@xxxxxxxxxxxxx> wrote:

<snip>
You can only do exact delays if the CPU is inherently deterministic.
The AVR is, but I do not know if the MSP is.
<snip>

I'm not sure you can call the AVR inherently deterministic. I never
forget to include hardware timer interrupt latency (this avoids
debates over recognizing/synching to an external event) variations. Is
it the case that upon a timer interrupt that there is an exact and
entirely predictable latency to the first instruction of the interrupt
code in the AVR?

Jon

It is for the purpose of implementing "__delay_cycles", but
there is certainly a couple of clock cycles variation
for interrupts

__delay_cycles(n) inserts a sequence of code which will take 'n' clock
cycles to execute without interrupts, regardless of the state of the
processor.

I dont think anyone using __delay_cycles can accept any interrupts.
If you need an exact delay you need a H/W timer and then
let other H/W react on the timer event.

I was just picking on your use of "inherently deterministic," Ulf.

I do use processors that actually _do_ have an exact and fixed latency
into interrupt routines no matter what else they may be doing and I
value that, for some applications, highly.

Jon
.

Relevant Pages

  • Re: What micros do you actually hate to work with?
    ... You can only do exact delays if the CPU is inherently deterministic. ... I'm not sure you can call the AVR inherently deterministic. ... forget to include hardware timer interrupt latency (this avoids ...
    (comp.arch.embedded)
  • Re: What micros do you actually hate to work with?
    ... You can only do exact delays if the CPU is inherently deterministic. ... The AVR is, but I do not know if the MSP is. ... forget to include hardware timer interrupt latency (this avoids ...
    (comp.arch.embedded)
  • Re: What micros do you actually hate to work with?
    ... You can only do exact delays if the CPU is inherently deterministic. ... I'm not sure you can call the AVR inherently deterministic. ... forget to include hardware timer interrupt latency (this avoids ...
    (comp.arch.embedded)
  • Re: Developing/compiling software
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