silverdr_at_inet.com.pl
Date: 2005-11-12 03:17:29
On 2005-11-11, at 21:22, David Wood wrote:
>>> No, there aren't enough cycles to decode to nybbles in realtime,
>>
>> Could you remind me how many of them are there in the worst case?
> I know its offtopic and we all love to hate apple,
;-) In EU we hated Spectrums... :-)
> but I read some
> interesting information in a hardware reference book. There's a
> GCR nybble
> exactly every 32 cycles. There's no byte ready line or other hint
> that a
> nybble was read. Just read, and -exactly- 32 cycles later, read
> again or
> miss a nybble. :)
Interesting. And how the first one was synchronised?
>
> The 1541 uses a variable bit clock, so it can vary, but the
> smallest sector
> count matches the evil system at 16/track, so it's probably not far
> off. ;-)
>
It is probably not far off the "evil system" but I'd like to be more
sure...
I understand that I have as much time as it takes for the next byte
to get shifted-in. Now this depends on bitrate so with the fastest
bitrate there will be the least time to do anything. Adding few
percents of contingency would give me safe result.
I recall I did those calculations some ages ago and I _think_ it was
something like
INT( (cpuclock/fastestbitrate) * 8 * (1 - 5%) )
As long as I didn't screw something, it should be enough to know the
fastestbitrate and the cpuclock numbers, which I don't remember ATM.
AFAIR the 1541 had slightly faster clock than the (PAL) 64 but the
bitrate? 320kb/s?
--
We do not inherit the earth from our ancestors, we borrow it from our
children.
Message was sent through the cbm-hackers mailing list
Archive generated by hypermail pre-2.1.8.