Date: Thu, 25 Sep 1997 10:56:16 +0930 From: Greg Lehey <grog@lemis.com> To: Nigel Gorry <nigel@4kz.com.au> Cc: questions@FreeBSD.ORG Subject: Re: Serial ports... Message-ID: <19970925105616.07116@lemis.com> In-Reply-To: <3.0.32.19970925110436.006f3e60@mail.4kz.com.au>; from Nigel Gorry on Thu, Sep 25, 1997 at 11:04:37AM %2B1000 References: <3.0.32.19970925110436.006f3e60@mail.4kz.com.au>
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On Thu, Sep 25, 1997 at 11:04:37AM +1000, Nigel Gorry wrote: > I am considering purchasing some serial cards that can be addressed as COM1 > - COM8 and have a choice of 9 IRQ's. > > Can FreeBSD support 8 com ports in one PC? Yes. > IRQ's are not a problem, because all the PC will have is a VGA & IDE > Controller, and all the other IRQ will be used for serial ports. They're still a problem. You don't have nearly as many IRQs as you think. Here's a rough map: /* Interrupt masks: mask word contains 16 bits, each masking an interrupt. * The hardware consists of 2 Intel 8259A interrupt handlers or workalikes. * Each interrupt handler can handle 8 interrupts, but they are cascaded: * ICU2's output goes to IRQ2 input on ICU2, which will then treat all ICU2 * interrupts at that priority. The motherboard IRQ2 line is in fact connected * to IRQ9 on ICU2. * Bit number corresponds to the IRQ. Interrupt usage for ISA motherboards: * * 0: Timer 0 (motherboard) * 1: Keyboard (motherboard) * 2: Cascade input from ICU2 * 3: free, usually com1 * 4: free, usually com0 * 5: free, usually lp1 * 6: floppy adaptor * 7: free, usually lp0 * 8: real time clock (motherboard) * 9: free, IRQ2 input * 10: free * 11: free, usually AHA disk interrupt * 12: free * 13: numeric coprocessor interrupt * 14: (wd) disk controller * 15: free, sometimes used for power management */ In other words, if everything goes well, you have a total of 10 IRQs available for all boards. You'll need: 1 IRQ for the disk controller 0 IRQs for the VGA (that's something) 1 IRQ for power management (probably) 1 IRQ if you have a network board installed That would leave you with only 7 IRQs. If you're not running a network board, how are you going to use the machine? My question, I suppose, is "does this board *really* use 8 IRQs?". Or do you mean that they're individual boards? Greg
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