Floppy controller questions

Dwight K. Elvey dwight.elvey at amd.com
Wed Aug 24 15:40:47 CDT 2005


>From: "Philip Pemberton" <philpem at dsl.pipex.com>
>
>In message <0ILP004N8EKHJER2 at vms040.mailsrvcs.net>
>          Allison <ajp166 at bellatlantic.net> wrote:
>
>> Unless you use a drive that spins faster then the 500khz rate is fine.
>
>If it doesn't, I'll speedhack it to run at 300.
>The only drive I've got that runs at 360 is a Y-E Data YD-380B. It completely
>ignores the speed select pin, even though it's wired to "something" on the
>PCB...
>There are no visible jumpers anywhere, besides DS0 and DS1.
>
>> Yep, remember the worst case for "fast is 13us!  I'd plan for that.
>> Also the slow rates will give you nominal 32us (27us worst case).
>
>Eek! Interrupt-mode it is then.

---snip---

Hi
 You might check the interrupt overhead. If you can't handle it
in polled mode, it is unlikekly that interrupt mode will keep
up. Although, the time between seeing the data available bit
and transfering the data is 13us, at 500Khz the bytes will
arrive at 20us rate. It changes what you need to do in which
order. Also, like I said in another post, if you know how
fast your processor is running, you may not need to check
the data available status every byte. Remember, they are
comming at 20 us each. You need to know the uncertainty of
the first status( how long it takes to loop on the status). 
 You also don't need to worry too much about the first data
available. Remember, the controller has to read across the
header and gaps before it needs to transfer any data.
Dwight






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