Re: BIOS behavior on BIOS and memory space enable bit

[wen-king@myri.com (Wen-King Su)]

>At 11:24 AM 9/4/96 PDT, you wrote:
>
>I doubt if the system BIOS is testing for memory BARs via the mem enable
>bit.  It's simple enough to determine if a board uses any memory BARs.  The
>usual sequence is to assign _all_ BAR resources (I/O & MEM), assign an IRQ
>if requested, then set the enable bits as required, then copy & init the
>expansion ROM via the ROM BAR (that's how my BIOS does it). 
>
>I agree that the enable bits should be OFF until a PCI board is properly set
>up, although, technically, any BAR set to 00000000h is disabled. At
>power-on, the board's hardware is responsible for clearing mem & I/O enable;
>during reset (soft or hard), the system BIOS often has to ensure that all
>PCI devices are disabled. This may be what you're seeing as 'fiddling'.

Thanks for the reply.  The mother board is made by ASUS, and the BIOS is
writing a '1' into the memory space enable bit before it write a valid
value into the BAR. 

I don't see how a BAR can be set to all 0, as there are hard-wire bits
in the lower 4 bit positions of a BAR.  If any of them are one, then it
can't be set to zero.  Perhaps you meant when the upper part of the BAR
is set to all zero, but I don't see where it says that in the spec. 
¿
$