[Coco] CoCo bitbanger does 115200 bps !

[Gene Heskett]

On Tuesday 04 April 2006 20:55, KnudsenMJ at aol.com wrote:
>In a message dated 4/4/06 8:39:46 PM Eastern Daylight Time,
>
>theother_bob at yahoo.com writes:
>>Way  Cool! How does this compare to the CoCo's normal speed floppy
>> disk access?
>>Also curious about double speed disk access (ala HDB-DOS)  and hard
>> drive access.
>
>Yeah, good stuff!  And I got excited a year ago when I figured out how
>  to read MIDI at 312500 bps (while parsing the MIDI 2- and 3-byte
> groups).
>
>ISTR the Coco floppy data rate is about the same, 100K/s, but I think 
> that's bytes, not bits, so floppy is still 8x faster.

Ahh, no.  When the data is actually flowing, its at 250 kilobits/second, 
either direction, which translates to somewhere around 30k bytes a 
second, but in practice is somewhat to quite a bit less due to the 
interleaving factor, usually 3.  When working on bru for the coco, I 
found the best write performance was at an interleave of 8, but 
recovery was january molasses slow at any interleave, mainly because 
the write housekeeping is so slow in bru that the disk makes 3 or 4 
revolutions while the last sector read from the floppy is being put 
away.  Writing I think the disk only turned somewhat over one rev 
between sector writes.  At an interleave of 7, it suddenly took 2x 
longer to write one disk as it had to make two revs to get back to the 
next sector.

>Hard drive access is always done via an intermediate hardware buffer
> of 256 or 512 bytes.  The bytes are read in/out by a tight software
> loop that goes between the hardware buffer and Coco RAM.  The faster
> the CPU and tighter  the code, the faster a whole file can be moved.
>--Mike K.

-- 
Cheers, Gene
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