Theodore Tso wrote:
>
> 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.
>
I have tried this on both a stock Redhat 7.0 kernel and on 2.2.19pre5 with
your serial-5.05 driver, and I could not measure any difference with and
without the "low_latency" parameter to setserial ....
#setserial -a /dev/ttyS1
/dev/ttyS1, Line 1, UART: 16550A, Port: 0x02f8, IRQ: 3
Baud_base: 115200, close_delay: 50, divisor: 0
closing_wait: 3000
Flags: spd_normal skip_test low_latency
The serial port chip is 16550A, which has a built in fifo. Can this be
the source of my problems ?
Geir
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:18 EST