From: drew@cs.colorado.edu (Drew Eckhardt) Subject: Re: 16550A FIFO IRQ setting question and ideas Date: Thu, 1 Jul 1993 00:14:15 GMT
In article <1993Jun30.062729.5571@unlv.edu> ftlofaro@unlv.edu (Frank Lofaro) writes:
>When doing a trace on a kermit process under Linux, data often came
>in in 8 byte chunks. I figured this might be related to the set-up of
>the FIFO's on the UART, i.e. how many bytes must be received before an
>IRQ is triggered. I looked through serial.c and serial.h and noticed
>that there is a FIFO control register which can set the FIFO trigger
>to either 1, 4, 8, or 14 bytes. It was set to 8, I changed the
>definition of the setup command to use a 14 byte trigger instead of
>an 8 byte trigger. Was this a good way to do it, or should I have
>gotten setserial, or changed some other file or something? Was this a
>good thing to do? It seems to work as far as I can tell. (tested both
>with ordinary logins and term/txconn sessions).
>
>What are the advantages/disadvantages of a high or low trigger rate? I
>believe high would favor higher throughput
A high trigger threshold will reduce the number of interrupts the
CPU must service, and keep things running smoothly since it
stays working on real jbos longer.
>and low would favor low delay.
Low trigger rate give more time before the FIFO gets full and there's
an overrun.
>If less bytes than the trigger come in, when is the FIFO
>drained?
A timeout interrupt will be generated if no characters are recieved
within the time it would take to recieve four characters.
-- Boycott USL/Novell for their absurd anti-BSDI lawsuit. | Condemn Colorado for Amendment Two. | Drew Eckhardt Use Linux, the fast, flexible, and free 386 unix | drew@cs.Colorado.EDU Will administer Unix for food |