PCI code: why need outb (0x01, 0xCFB); ?
Quoted 4 lines · H. Peter Anvin
Quoted 2 lines
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 [email protected]
Quoted 10 lines · Petr Vandrovec
Quoted 3 lines
Quoted 1 line
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 at0xCFBto 1 before doing PCI config accesses and reset it back to original value afterward.
Quoted 5 lines
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 :-(
Fortunately that's not true. Grab the relevant docs from:
'ftp://download.intel.com/support/chipsets/430nx/'. The semantics of 0xcf8, 0xcf9, 0xcfa and 0xcfb I/O ports when used as byte quantities is explained there. Note that 0xcf8 and 0xcfa are the way to get at the PCI config space using conf2 accesses.
Signature · 3 lines
+ Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: [email protected], PGP key available +