On Mon, May 11, 2020 at 09:41:27AM -0400, James Knott via talk wrote: > I used to be a computer tech, on the big systems. I also designed and built > an 8 serial port card for my IMSAI 8080. In all my experience, I had only > seen level triggered interupts or IRQs. This meant when something needed > service, it would pull the signal line low. This allowed multiple devices > to share 1 interrupt line and the OS would sort out which needed to be > serviced. IBM, instead of using that common practice, when with rising edge > triggers, which cannot be easily shared. The Intel interrupt controller > chip that was used supported either mode, so there was no valid hardware > reason, that I could see, for IBM to choose that method. If they had gone > with level trigger, then we wouldn't have had that IRQ sharing mess we had > to deal with on the PC/AT bus.
I wonder if edge triggered allowed for dumber devices since the device doesn't need to be able to latch the interrupt until serviced. I could imagine anything that could make the IBM PC cheaper was considered worth doing (like the 8 vs 16 bit data bus by using the 8088 rather than the 8086). But yes edge triggered interrupts are awful. -- Len Sorensen --- Post to this mailing list [email protected] Unsubscribe from this mailing list https://gtalug.org/mailman/listinfo/talk
