[Coco] Re: atari USB device

[Mark McDougall]

Torsten Dittel wrote:

> I had a quick view on the data sheet of that chip and it looks like it
> only has 240 usable (from 256) bytes of data buffer. Not enough to hold
> a disk sector. This will make the CoCo slow for other tasks than USB
> access. AFAIR people started to build "No Halt" controllers with sector
> buffered Disk I/O 20 years ago for that reason.

USB data packets (at least v1.x) are only 64 bytes in length. So I'm not 
sure what the 240 bytes refers to in your post. With the USB protocol 
handling the handshaking the CoCo is left to emptying the 64-byte packets as 
fast (or as slow) as it likes. I really don't see an issue here...

As James has re-iterated, we should be worried about 'crawling' first. The 
idea is not to be able to hook up 10,000RPM raid arrays and broadcast 
quality video digitisers. A USB interface merely opens up possibilities of 
interfacing modern devices (keyboard, mice, flash disks) purely for the 
'because we can' factor and also for convenience.

As much as we love our CoCos and insist that we can still be productive on 
them, the fact is that we're talking about a 2MHz 8-bit CPU - the embedded 
8051 core in the Cypress EZ-USB slave chip itself runs at 12 MIPS!!! One may 
argue that what we're trying to do is quite silly and perhaps futile - but 
damn it's FUN!!!

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
| <http://members.optushome.com.au/msmcdoug> |   with less resistance!"