Re: [TCLUG:224] RE: LUG - bash error and fat32

[Michael Hicks <hick0088@tc.umn.edu>]

> If anyone ever wondered what the difference between the 16550A and 8250
> UART serial ports are: The 8250 has a 38400 bps max and the 16550A runs
> up to 115200 bps. With today's high speed modems (I use that term
> loosely) make sure you have a 16550, since with compression, you can
> potentially reach speeds > 38.4K.
> 
> The winmodem tried to cut the cost by eliminating the UART chip and
> having the software do the work. Not a wise move. It takes too much CPU
> time to do this. Hardware should be doing more work, not less.

IIRC, the 16550A was the first one of these UARTs that had a buffer, and
it still only has a 16-byte one.  (I think.. I haven't looked at this
stuff for at least a year, probably two..)

Previous UARTs would trip an interrupt for every byte, or at least a
very small set of bytes.  The buffer in the 16550A allowed it to be used
in lower performance computers that couldn't handle an interrupt for
every byte on a 14.4 transmission (this would be like 286s and less..),
since the interrupt only had to go up only when the buffer filled up.

Anyway, I've seen many comments on how small the buffer is..  by all
rights, it _should_ be a kilobyte or so..  Especially in a multitasking
environment.  But, of course, it doesn't matter a whole hell of a lot
with faster computers..

Mike Hicks