16550 THRE

[crompton@NADC.NADC.NAVY.MIL (D. Crompton)]

Can anyone explain the THRE TO vs. NOS to a little more detail than the
one sentence in the manual.

I recently switched from a slow XT where I got no THRE TO's to a
much faster 386 system and I get occasional THRE TO's. I am using the
same I/O card and UART's from the old system. IT does not seem to effect
performance although the existence of the TO probably indicates lost
data???

In an attempt to see if it would help I recompiled the code with
the TX buffer size set to 16 characters rather than 1 and the fifo
limit to 4 rather than 1. The values of 1 were used by Kelvin early on
when there were troubles and has been historically carried on since.

It did not seem to make a difference with the THRE TO's though. It
now does show 16X more TX characters than TX interrupts. And 4X more
RX characters than RX interrupts.

What is the desireable setting for these two values? Is it good to
minimize the number of interrupts and maximize the number characters
transfered at each interrupt?

Set the way it currently is with the PA0 code it interrupts on each
character TX and RX.

I guess I never really understood the TX interrupt problem. That is
generally where more problem seems to exist but why is this the case.
I have the character to send and as long as I have enough room to
store them all should be well. On the other hand on RX something is
trying to dump characters to me and if I do not service it often enough
characters will be dropped. Seems yoiu have much more control over TX
than RX. What am I missing?

I never see RX hardware overflows.

Any insight on this would be appreciated.

Doug