alex.freed.007{at}gmail.com wrote:

> I understand that the main attraction of CP/M was portability and
> ideally the
> programs ran on any CP/M platform. However looking (for the first
> time) at
> the concept of "overlays" for different computers that apparently
> served as low
> level device drivers it becomes clear that portability was not 100%.

Not for things that talked directly to hardware, no.

> PCPI card is very interesting because it's a multiprocessor system. It
> may be
> a good exercise to write a file transfer program with the SSC
> interface running
> on the 6502 side. Just like a disk driver. Serial port may be a
> "character device"
> but it becomes a block device for xmodem protocol. So 6502 can get a
> 128 bytes
> block via SSC at 19200 baud  and give it back to z80 all at once.

That's precisely what the ringbuffer driver does.  I'll get the disk image to 
you tomorrow.

Steve
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