Re: Serial port latency

[Theodore Tso <tytso@mit.edu>]

On Thu, Mar 22, 2001 at 07:21:28PM +0100, Geir Thomassen wrote:
> My program controls a device (a programmer for microcontrollers) via the
> serial port. The program sits in a tight loop, writing a few (typical 6)
> bytes to the port, and waits for a few (typ. two) bytes to be returned from
> the programmer. 

Check out the man page for the "low_latency" configuration parameter
in the setserial man page.  This will cause the serial driver to burn
a small amount of additional CPU overhead when processing characters,
but it will lower the time between when characters arrive at the
RS-232 port and when they are made available to the user program.  The
preferable solution is to use a intelligent windowing protocol that
isn't heavily latency dependent (all modern protocols, such as kermit,
zmodem, tcp/ip, etc. do this).  But if you can't, using setserial to
set the "low_latency" flag will allow you to work around a dumb
communications protocol.

						- Ted