7300 and 9600 baud modems (VT220 suggestion, and question)
John McMillan
jcm at mtunb.ATT.COM
Tue Dec 5 09:08:00 AEST 1989
In article <1846 at neoucom.UUCP> wtm at neoucom.UUCP (Bill Mayhew) writes:
>
>I don't have any problems with my Trailblzer on my 3b1. I've been
>using a TB since 11/1987. I started with one of the old version
>3.1 TBs and then switched to the white-cased TB+.
I'm totally 8-) for you!
>The problem of over-runs happens when you use in-band signaling
>with xon/xoff.
There are three principle overruns:
- RS-232 Chip overruns
- 'seriobuf' overruns
- C-list overruns
The former occur when the duration of "high-level" interrupts
exceeds ~2 * receive-time for a single character. This
*DOES* occur, and it's easy to produce using a terminal
off any port to CU to another system at 9600 baud.
Just CAT a file and watch the bytes get lost. Then do
a "~%take" into a file: all characters will be received,
indicating it was the load associated with the DISPLAY of the
characters to the terminal that induced the chip-overrun.
'seriobuf' overflow occurs when sustained low-level interrupts
prevent the unloading of this temporary buffer into the
C-list mechanism.
C-list overruns occur when the CPU-usage is so high that
user programs cannot read the data as fast as it is
arriving and the C-list use-limits are being circumvented.
Flow-Control (H/W or S/W) can deal with this, and only with this.
The preceding comments are probably flawed -- I've other things to
deal with -- but they're pretty accurate!-)
john mcmillan -- att!mtunb!jcm -- tic-toc-tic-toc...
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