[Coco] DW and 6551

[Gene Heskett]

On Tuesday, February 10, 2015 06:35:06 PM Aaron Wolfe wrote:
> There was a driver at one point, but I don't think anyone maintains it
> and so I don't think it was converted to the modular system we started
> using a while back.  In the time since that document was written I
> think it's realistically changed to "not supported".  Writing a driver
> for the 6551 would not be very difficult but since it's so limited in
> speed compared to the bitbanger I think there is little interest.

Its been done but a while back now, the joydrv_sc6551L.sb I wrote for my 
seriel mouse is I believe the last one.  By the time its done semi-
correct, its a bit bulky too IMO.  Heck, just the src is north of 18 
kilobytes.
 
> On Feb 10, 2015 6:30 PM, "Joe Grubbs" <jsgrubbs at hotmail.com> wrote:
> > Another DW question... I noticed that the feature list for DW says
> > that 6551 support is "very limited". What does this mean exactly?

Speed limited in that the chip itself has no input buffer, just the data 
register, which must be read before the next byte arrives else it throws a 
framing error. Some protocols can tolerate that at 9600 baud, but rzsz 
must have a working flow control above 2400 baud or it upchucks all over 
itself. rzsz is not even able to cope with 4800 baud in a 6809, & 
something in the 6500 baud range can be done on a 6309.  Adding more 
buffer to the driver with a non-zero setting in the 2 lsb's of both  xtp 
nibbles only puts off the inevitable error recovery a couple seconds as rz 
simply cannot read it fast enough.

> > I would check the documentation on SourceForge, but I get a 404 error
> > and a message about their content being offline for now.
> > 
> > --
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> > Coco at maltedmedia.com
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Cheers, Gene Heskett
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