[Coco] CoCo Ethernet for $25-$30...

[Aaron Wolfe]

On Mon, Apr 8, 2013 at 5:37 PM, Bill Gunshannon <billg999 at cs.uofs.edu> wrote:
>
>>
>>
>> I would very much like to put a Pi in a ROMPak (it fits perfectly!).
>> However, using a serial interface is just slow and cumbersome... We
>> need a way to interface from the Pi to the bus directly, especially
>> since then we could build the Pi into a usable rompak that you just
>> plug in and go.
>
> You say the serial is too slow.  I have seen peopl ehere talking about
> running DW at 115K and 221K.  Just what is the bus speed of the COCO?
> It would seem to me that either of these wold saturate the bus on a
> 6809.
>
> As one who remembers when 56K was blistering network speed often
> supporting entire campuses, I would be very happy with 115K - 221K.
>

Yes, DriveWire operates at 115K, or 230K in some situations.  However,
doing this requires that interrupts are disabled and the 6809 is
entirely dedicated to the serial I/O during the transfer.  It also
requires that the CoCo *always knows* when data is to be received, it
essentially must busy wait to be ready for data.  This is part of the
"cumbersome" aspect of high speed serial on the CoCo... it is not
truly bidirectional, all operations must be initiated by the CoCo side
and the CoCo must always known exactly how many bytes are going to be
sent by the host side prior to their being sent.

So essentially, high speed serial is resource intensive and disruptive
to multitasking or any other I/O, and difficult to program for.
DriveWire makes most of this hidden for the user and provides standard
SCF devices they can use without worrying about the nasty business
going on behind the scenes, but it is still limiting.  For instance,
we can do MIDI out using the bitbanger, but we could never do MIDI in
(without dedicating the entire CPU to nothing else, always, not even
having time to do anything with the MIDI data received).

As for the I/O capability of the CoCo, both floppies and hard drives
vastly outpace 115Kbps throughput.  Floppies lose overall due to very
high seek times, but a modern disk controller like the SuperIDE
transfer data in the 1000s of Kbps.

115k is good enough for telneting into your coco, even a few sessions/users.
However, it is pretty painful when used as a web server or to transfer files.

-Aaron