🚀 go-pugleaf

In article <j3t89s88tmqegcp4luu8bmh18l3mmbsc1v@4ax.com>, Harry Broomhall
<haeb@pc60.easynet.co.uk> writes

>   I don't agree with this.  My POST card has fairly often pointed me
>at the problem.  Typical items were 'faulty cache' on older Socket 7
>mobos,

'faulty cache' could also cover faulty processor, faulty cache
controller, and faulty or incorrectly fitted memory.

> and that hardy perenial, VGA card not working.

wouldn't you in that case hear the 'VGA failure' beep sequence from the
BIOS's POST?

>   The other main use is to see if the machine starts at all.  Without
>a POST card it is very hard to know if the machine has failed to boot
>because of a faulty VGA card or cache or what ever, or just hasn't
>started.

Agreed, but it's possible to make an intelligent guess from other clues.
For instance, you can feel the temperature of the CPU with the back of a
finger.  An excessively hot or cold CPU indicates a problem.  I've had
several boards with secondary power failures (the on-board circuitry
used to produce the 2.2 -to- 3.2 volt core CPU voltage)

>   POST cards don't access a bus at all.  The way they work is much
>simpler than that.  During POST (Power On Self-Test) the processor
>carries out a lot of tests on the hardware.  At each stage it writes a
>value to port 80H to indicate where it has got to.

You're quite right.  I'd allowed myself to be led astray by the multi-
functional nature of the RACER POST card I used to use.  That did more
than just display the results of POST at port 80.

It's worth noting that the meaning of the number sent to port 80
differed from BIOS maker to BIOS maker, and so a look-up list is needed
to see what a certain figure means.

>   In the early stages of POST, before the VGA card is woken up, a
>failure of a test will usualy put the processor into either a HALT or
>a tight loop.  At this point the value displayed can be looked up in a
>table to get a guess as to what is wrong.

I will admit, POST cards can be useful.  My argument was that knowing
that, for example, the DMA controller has failed is of little use when
the easiest and quickest route to curing that failure is motherboard
replacement.

-- 
Mike Tomlinson