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From: langwadt on 17 Dec 2009 17:29
On 17 Dec., 22:17, "Steve at fivetrees" <st...(a)NOSPAMTAfivetrees.com>
wrote:
> <langw...(a)fonz.dk> wrote in message
>
> news:69d93693-d2df-43af-9d28-b04b4235f8cb(a)c3g2000yqd.googlegroups.com...
>
>
>
> > would a 200KHz interrupt really be that bad?, write it in assembler if
> > needed,
> > can't be that many instructions if all it needs to do  is copy a few
> > bytes and return.
> > I'd rather use 5-10% of the cpu on an interrupt than try to try and
> > kludge together
> > fifos and a bunch of logic and hope it works.
>
> One of my colleagues has already tested this idea, by injecting a 200kHz
> signal into an IRQ pin. He tells me there's time for the ISR to be called
> and to return, and almost nothing else. Certainly not time enough to do
> anything useful.
>
> I've not double-checked his work ;).
>
> Steve
> --http://www.fivetrees.com

At what speed are you running it? maxed out by a simple 200KHz
interrupt
doesn't sound right

-Lasse
From: don on 17 Dec 2009 17:59
langwadt(a)fonz.dk wrote:
> On 17 Dec., 22:17, "Steve at fivetrees" <st...(a)NOSPAMTAfivetrees.com>
> wrote:
>> <langw...(a)fonz.dk> wrote in message
>>
>> news:69d93693-d2df-43af-9d28-b04b4235f8cb(a)c3g2000yqd.googlegroups.com...
>>
>>
>>
>>> would a 200KHz interrupt really be that bad?, write it in assembler if
>>> needed,
>>> can't be that many instructions if all it needs to do is copy a few
>>> bytes and return.
>>> I'd rather use 5-10% of the cpu on an interrupt than try to try and
>>> kludge together
>>> fifos and a bunch of logic and hope it works.
>> One of my colleagues has already tested this idea, by injecting a 200kHz
>> signal into an IRQ pin. He tells me there's time for the ISR to be called
>> and to return, and almost nothing else. Certainly not time enough to do
>> anything useful.
>>
>> I've not double-checked his work ;).
>>
>> Steve
>> --http://www.fivetrees.com
>
> At what speed are you running it? maxed out by a simple 200KHz
> interrupt
> doesn't sound right
>
> -Lasse

200KHz is 5uSec per interrupt.

An ISR that takes 5uSECONDS !!!

Yes, this does not sound right.

What processor and speed are you (OP) using ??

A Z80 at 4MHZ interrupt is less than 5uSec.

don
From: Steve at fivetrees on 17 Dec 2009 18:03
<langwadt(a)fonz.dk> wrote in message
news:1f3badfd-60c3-4a91-9ee2-23aac675097a(a)m25g2000yqc.googlegroups.com...
On 17 Dec., 22:17, "Steve at fivetrees" <st...(a)NOSPAMTAfivetrees.com>
wrote:
> <langw...(a)fonz.dk> wrote in message
>
> news:69d93693-d2df-43af-9d28-b04b4235f8cb(a)c3g2000yqd.googlegroups.com...
>
>
>
> > would a 200KHz interrupt really be that bad?, write it in assembler if
> > needed,
> > can't be that many instructions if all it needs to do is copy a few
> > bytes and return.
> > I'd rather use 5-10% of the cpu on an interrupt than try to try and
> > kludge together
> > fifos and a bunch of logic and hope it works.
>
> One of my colleagues has already tested this idea, by injecting a 200kHz
> signal into an IRQ pin. He tells me there's time for the ISR to be called
> and to return, and almost nothing else. Certainly not time enough to do
> anything useful.
>
> I've not double-checked his work ;).

>>At what speed are you running it? maxed out by a simple 200KHz interrupt
>>doesn't sound right <<

66Mhz. Yes, I know. But this particular chip saves an awful lot of context
to the stack (not the compiler - the chip itself, IIRC). There's a bank of
registers which is saved and restored to make them available to the ISR.

Also I may be misrepresenting my colleague's work. I trust him, he knows
what he's doing. He tells me there's not enough time (5us total) to kick off
an SPI DMA transfer (which takes about 2us to start up, and then further
time to run...).

In any case, we have a more elegant solution, so the point is now moot.

Steve
--
http://www.fivetrees.com

-Lasse


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