From: tytso@ATHENA.MIT.EDU (Theodore Ts'o) Subject: Re: 0.98 and serial ports, IRQs Date: Sat, 3 Oct 1992 01:47:22 GMT
From: james@netcom.com (James L. Paul)
Date: Thu, 1 Oct 1992 17:03:57 GMT
I noticed in 0.97.6 and above (0.98) that serial has been extensively
changed. I'd like to add up to 8 more ports. What is my best option for
doing this?
1. Can I add more 2-port cards and share IRQs? How do I set this up?
Not without some really serious hardware hacking. The general answer is
"no". See below to question #5....
2. Can I add 2 AST Fourport cards to get a total of 12 ports? How?
Yes; the AST FourPort card can live at two different addresses,
0x1a0-1bf and 0x2a0-2bf. I currently have 10 serial ports on my system
(COM1+COM2, and two AST Fourport cards.)
3. Can I get 4 or 8 port cards other than the AST? Which cards work?
The Accent Async board works as well; that gives you two ports at COM1
and COM2, and two other ports which are supported by the Linux serial
driver.
It probably isn't hard to get other cards to work, but you would need to
have the technical specs on how they work. If you like, send them to me
and if it's not too hard, I'll look into trying to make them work. If
you really want to see a particular card supported, sending me a sample
of the board itself will make it much more likely that I will try to
support it. :-)
4. What issues are involved with sharing IRQs between ports on a board?
Your board has to support it; if it doesn't, you're screwed.
5. What issues are involved with sharing IRQs across boards?
In general, you can't, unless you do some hardware hacking; this
involves cutting the trace to the IRQ lines, running the IRQ line from
both boards to a separate prototype board where you wire in an OR
gate.... you get the idea. Not an easy thing to do.
There is also rumored to be a black magic solution involving analog
devices which you put into a digital circuit, but I'm sure it's got to
be outside the TTL specs; I don't know much more about it.
6. If I set 2 ports to the same IRQ, do they also share the COM address.
You don't want to do this; if you do, both ports will conflict with each
other and both will not work. Either trying to setting both ports to
use the same IRQ or use the same COM address will cause you to lose.
The only exception is on multi-port boards which are *designed* to allow
ports on that card to share a single IRQ, such as the AST Fourport card.
- Ted