debugger

[Adam Sulmicki]

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.

-- 
Adam Sulmicki
http://www.eax.com 	The Supreme Headquarters of the 32 bit registers