[Coco] Internet/BBS connectivity via Coco1

[Gene Heskett]

On Friday 03 January 2014 08:20:07 Bill Pierce did opine:

> So the Coco's just kool :-)
> BTW.. what baud would I use in supercomm?
> 
> Bill Pierce

On a real coco, the usual rzsz protocol will be all tapped out at 4800 
baud, other protocols can be much faster.  On a 6309 coco, there is a wee 
bit more headroom, but while text, without crc driven error corrections of 
zmodem can be moved at 56k, zmodem is going to need a fully working 7 wire 
protocol to get into the 7000 baud range.  zmodem itself has been enhanced 
on other platforms to use really big "windows" that can if not restrained, 
totally overpower the rzsz we have.  Since the 6551 isn't capable of 
properly doing a 7 wire protocol, it is best to avoid speed or window 
settings on the host sending the data which will encounter the need for 
flow control.

On this linux box, I find I can use 9600 baud 8n1 by restricting the zmodem 
"window" size to 256 bytes, which well matches the capability the rzsz we 
have by sending only 256 bytes and pausing until the coco has returned a 
"checksum good" back to the host machine.  The overhead of this small a 
"packet" being sent, and waiting for the checksum good return will actually 
get you about 640 cps steady and error free, equ to about 6400 buad, and 
will move a 720k .dsk image in the least time by a very wide margin.

Forget to do that, and you will see zmodem sending 8k or more in one block, 
and the two protocols will sit and discuss where they are at in the file, 
try a smaller block repeatedly until they succeed, but the zmodem here will 
try to send a bigger block the coco cannot handle (unless the flow controls 
are working), then it repeats and will take half a day to move a 720k .dsk 
image.  That gets plumb painful to watch. Particularly when it crashes the 
coco and you have to delete the partial files and start all over.

20 years ago, I did have an sacia + t2.dd descriptor setup that did appear 
to do the 7 wire protocol flow controls well, and I should extract those 2 
modules from a boot disk I have labeled Old Faithful and incorporate them 
into a modern build.  But with my salt chip blown, thats not going to 
happen until the new ones arrive.

Cheers, Gene
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