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Re: tty with non-standard irq



On Aug 18, Joost Kooij wrote
> 
> Um, I don't think it is a very healthy practice to use irq 2 for a serial
> port. 
> 
> Irq 2 is called the "cascade interrupt". Pc-xt's, which have only one
> interrupt controller, have 8 irq's, but in at's a second controller is
> cascaded from the primary interrupt controller's irq 2 to yield a total of
> 15 usable interrupts (because you cannot use irq 2 for a real interrupt
> anymore.) Read a pc-hardware faq if you want to know more about this. 
> 
> So unless you are running linux on a 8086, you can forget irq 2, I think. 

I've been using this on my (internal) modem for a while now and havn't
seen any problems - I used to get the full 3+Kbps that my modem can
manage - but now I've moved and had an extension put in and it doesn't
seem as good :-(

As has been pointed out, it is also IRQ9 (win95 can't cope with 2!, and
the modem doesn't have a jumper for 9)

If this really is a problem, please let me know (but I've no idea which
IRQ to use as most of the rest seem used up by various strange things!)

Adrian
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