multiple com ports on same irq

QNX Newsgroups (Archives) qdn.public.qnxrtp.os
1

I was reading some of the QNX doc last night and it mentioned that the
devc-ser8250 was capable of providing service for multiple serial
ports sharing the same interrupt. Has anyone tried to put COM3: &
COM4: or perhaps COM1-COM4 all on one interrupt? Does anyone
know of any reasons that this should not work as documented.

Thanks,
Carlton

2

“Carlton Haycock” <chaycock@bytewise.com> wrote in message
news:yeQDPB92DZeQ+RyTweDOrx4iHVc1@4ax.com…

I was reading some of the QNX doc last night and it mentioned that the
devc-ser8250 was capable of providing service for multiple serial
ports sharing the same interrupt. Has anyone tried to put COM3: &
COM4: or perhaps COM1-COM4 all on one interrupt?



Does anyone
know of any reasons that this should not work as documented.

Yes, usually the problem is hardware. For example a ISA modem
on COM3 will conflict with COM1. ISA interrupt cannot be shared, (some
board do allow sharing ISA interrupt but only between themselves)


Thanks,
Carlton

3

Carlton Haycock <chaycock@bytewise.com> wrote:

I was reading some of the QNX doc last night and it mentioned that the
devc-ser8250 was capable of providing service for multiple serial
ports sharing the same interrupt. Has anyone tried to put COM3: &
COM4: or perhaps COM1-COM4 all on one interrupt? Does anyone
know of any reasons that this should not work as documented.

It will handle this on a multi-port serial card where the card handles
the or-ing of the interrupt lines properly.

It will not handle this if you put two independent cards on the same
irq on the ISA bus. (Doing this will result in that IRQ going into
a state where another IRQ is never generated again – an effect of
edge-triggered interrupts. The only work-around would be to regularly
poll your hardware – we do not poll in our driver.)

-David

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