On Thu, 15 May 2003, jarcher wrote:
A POST (power on self test) card is basically a dumb card that decodes an I/O port (80h) and displays the value. Nothing but the CPU access to the ROM and I/O bus (PCI or ISA) has to work to access the card.
mov al, CRUMB_1 out 80h,al
Speaking of PORt-80 cards. Something I was wondering about is how are they implemented from technical viewpoint. Anyone care to elaborate?
Is chipset support required for such card to work? Would this be south-bridge? What exactly gets send over PCI/ISA bus. Also Compaq seems to use port 84.. would this mean they switched some GPIO leads to south bridge that make POST card?
Speaking of those stuff it reminds me Alpha which had like 4 leds on motherboard. However unlike POST on x86 it was memory mapped instead of port mapped. So you would simply write into memory. Obviously my expereince with Alpha was from OS perespective so not sure if those debugging leds would work from PROM level as well.