Re: [Etherboot-developers] NE2k probing

[Markus G. <ma...@gu...>]

> Since ethX is brought up well before sound in this case, would it not make
> sense to probe there?  Even if there happens to be a sound card there, I
> dont think it would cause any trouble....  I might be wrong here though, I
> know absolutly nothing about C, let alone programming hardware stuff.

Legacy hardware (and most ISA bus hardware should be considered as
such) is really troublesome. You cannot reliably find out which
hardware is installed unless you start probing for it. Probing
involves writing (bad idea) or reading (only slight better) from
I/O addresses and ports where you might expect hardware to live. If
you see a pattern that you recognize, you assume that a particular
piece of hardware has been installed in the machine. The problem here
is that a) you might not always recognize a signature properly, and
b) even reading from ports and address can reconfigure hardware. The
latter can result in all kinds of unexpected behavior, from the
hardware just becoming unavailable to the entire machine crashing.
Thus, you must be extremely careful when probing and you should try
to touch as few addresses as possible. You might remember, that for
a very long time, Linux had problems with the initialization order of
device drivers, because there where rather tricky requirements as to
in which order autoprobing should be done. With the gradual
disappearance of ISA bus hardware this has now become better. ISA PnP
is some improvement (though still pretty ugly), PCI is a lot better,
and both PCMCIA and USB have enough meta information to properly
detect hardware and automatically load the right drivers.


Markus

-- 
Markus Gutschke                                Resonate, Inc.
3637 Fillmore Street #106                      385 Moffett Park Drive
San Francisco, CA 94123-1600                   Sunnyvale, CA 94089
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