Hardware Installation

IRQ Sharing Issues

Many telephony cards such as the X100P tend to generate a large amount of interrupts. Servicing them takes time and drivers may not be able to do it on-time. If another device is processing the same shared IRQ, the IRQ line cannot receive another one. It does tend to work better on SMP (APIC) systems. On single chip systems you can get interrupt misses and messed up clocking. Any of Digium's cards or other telephony cards can be subject to this problem. Because the precise delivery of IRQ's is very much necessary in telephony, one should not share IRQ's with anything. This is not to say you will necessarily have IRQ sharing conflicts, but it is something to be aware of.

If you are dedicating the computer to Asterisk, free up the most IRQs as possible by disabling USB, serial and parallel port support in the BIOS. Essencially you want to free as many IRQs as possible. You will *not* want to see a NIC sharing an IRQ with a TDM or FXO card! It's best that these cards have their own IRQ.

Most BIOS' will allow you to manually assign IRQs to specific slots. Go into the BIOS and look for the IRQ area, often on the second page. If it is set to AUTO by default, try setting to manual and see what happens. Chances are, a table will become available for manually assigning an IRQ to each slot.

Note: One thing to watch out for on some motherboards is slots *sharing* IRQs. Look in the BIOS and check if it has an entry like "1/5" in the IRQ table.

Once booted, view /proc/interrupts to see the assigned IRQs.

(output below is just an example with Digium hardware flagged)


			# cat /proc/interrupts
			            CPU0
			    0:   41353058          XT-PIC  timer
			    1:       1988          XT-PIC  keyboard
			    2:          0          XT-PIC  cascade
			    3:  413437739          XT-PIC  wctdm <-- TDM400
			    4:    5721494          XT-PIC  eth0
			    7:  413453581          XT-PIC  wcfxo <-- X100P
			    8:          1          XT-PIC  rtc
			    9:  413445182          XT-PIC  wcfxo <-- X100P
			   12:          0          XT-PIC  PS/2 Mouse
			   14:     179578          XT-PIC  ide0
			   15:          3          XT-PIC  ide1
			NMI:          0
			ERR:          0
			

Above you can see the three Digium cards each on its own IRQ. If this is the case, you can go on to install hardware drivers.

Digium Cards