serial ports on the '286

[James Van Artsdalen]

In article <4690 at b-tech.UUCP>, zeeff at b-tech.UUCP (Jon Zeeff) wrote:
> I think serious thought should be given to supporting the NS16550AN.  
> This is a plug in replacement for the existing uart that gives you a 
> 16 byte fifo.  At least the problem would go from "there is nothing 
> that can be done" to "you need to buy a new chip".  I don't know what 
> the cost is though.  

I believe the part has settable high- and low-water marks also.  This
means that it can not only prevent lost characters at high speed (due
to the kernel having interrupts disabled for long periods), but is can
also lessen the system load at high speeds by dramatically cutting the
number of interrupts to be serviced.

For example, let's suppose uPort modified the serial driver such that
when the line was put in raw mode, the 16550AN was set to generate an
interrupt every tenth character.  The interrupt handler would then get
ten bytes for the overhead of one interrupt, and would still have six
character times to respond to the interrupt.

I think it patently obvious that such a driver would not only let all
of the machines run Trailblazer+ at 19.2Kbps, but that it would do so
with less system load than 2400bps current takes.  There would be a
higher user-level load because uucico would be doing more file writes
and checksum calculations, but I think we could all live with that.
I find it somewhat annoying right now that I can't run my TB+ at
19.2Kbps under any conditions with a fast 386.  >:-(

As a subtle hint to the various vendors taking a break from the flame
wars, you can buy these nifty parts from Arrow Electronics for about
$22.  Their phone number is 1-800-932-7769.  You want the 16550AN
part, not the 16550N (the N suffix is just package type: the A is
significant).  I've already got one sitting in my serial board to
prove compatibility - I'd be happy to beta test (hint, hint).
-- 
James R. Van Artsdalen    ...!uunet!utastro!bigtex!james     "Live Free or Die"
Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746