🚀 go-pugleaf

In <10595@spool.cs.wisc.edu> so@brownie.cs.wisc.edu (Bryan So) writes:

>Somebody must have posted this before, but I am relatively new to 
>this newsgroup, so... can somebody show me the general method to
>speak to COM3 and COM4?  Can I simply service IRQ3 & IRQ4 as if
>they are COM1 and COM2?

In general, yes.

>If so, how can I distinguish whether the
>interrupt is raised by COM1 or COM3 (take IRQ3 for example)?

Test each UART's EID register.  Bit 0 will be low if there's an
interrupt active.  The rest of the bits in this register identify
the interrupt type(s).

Most cards with 4 ports don't support sharing of interrupts between 
ports correctly (unless they explicitly state that they do), but if
they do you can look at both to determine which it was.  Depending
on the speed of the links, you may have to service received characters
on both ports before moving on and servicing other less urgent
things.


david

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