Re: PCI code: why need outb (0x01, 0xCFB); ?

Petr Vandrovec
2003-01-08T20:40:54Z

On 8 Jan 03 at 10:52, H. Peter Anvin wrote:
>
> > 1. which device is at port address 0xCFB?
>
> Hopefully none.

Actually I'm not sure. This code is here since at least 2.0.28,
and during googling I even found code for direct PCI access
(http://www-user.tu-chemnitz.de/~heha/viewzip.cgi/hs_freeware/gerald.zip/DIRECTNT.CPP?auto=CPP)
which sets lowest bit at 0xCFB to 1 before doing PCI config
accesses and reset it back to original value afterward.

So I believe that there were some chipsets (probably in 486&PCI times)
which did conf1/conf2 accesses depending on value of this bit.
Unfortunately I was not able to confirm this - almost nobody provides
northbridge datasheets from '94 era, even Intel does not provide them
(f.e. Neptune) anymore :-(
Best regards,
Petr Vandrovec
vandrove@vc.cvut.cz