Subject: Re: Sparc Classic serial (zstty) max bps
To: Tim Walls <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: port-sparc
Date: 04/25/2000 13:16:42
> My only remaining question <grin> is of the serial port speed.  Can
> the serial port of the Sparc Classic (and pppd) be coaxed into
> working at speeds > 38k4?

pppd will probably do it if the serial port driver is willing to.

> Could anyone let me know if it's possible?  Vague memories suggest
> there may be some cleverness required setting additional flags in an
> IOCTL in addition to just specifying a higher baud rate than 38k4,
> but that could just be a total red herring <grin>.

I think it is.

The clock driving the chip is nominally 4.9152MHz.  If the BRG chain is
run in divide-by-16 mode (which it normally is), this means the highest
speed available is 4915200/16/4, or 76800.  This should be attainable
with no problems.  (The next lower speeds: 4915200/16/6=51200,
4915200/16/8=38400, .../10=30720, .../12=25600, 21942.857+,
particular, 57600 is not attainable.)

It is possible to run the chip in divide-by-1 mode; I have patches to
do it.  But you may well not want to, because the lack of sub-bit
sampling means character reception is no longer particularly reliable -
most characters will probably be received OK, but you can expect bursts
of errors as the transmitter and receiver clocks drift into and out of
phase with respect to one another.  Depending on what you're doing,
this can be anything from ignorable to particular, if
you're doing send-only, and the receiver can reliably receive at high
speed, it won't matter that the SPARC can't receive reliably.  But PPP
isn't send-only....

					der Mouse

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