Re: PCI 64-bit addressing - problem

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

>I see that the PC allocates us in a 64-bit address space. This I see by the 
>fact that the PC configures two consecutive memory base address registers: 
>the PC configures a value of 0xFFA0000C in memory base address 0x10 and a 
>value of 0xFF in memory base address

We have found that often the high half of the BAR is not set to zero not
because the computer knows how to generate a 64-bit address, but because
the software does not know how to properly initialize a 64-bit BAR and
leaves junk in the high half.  The behavior differs from system to system.
What we ended up doing is to add a mechanical switch that causes our ASIC
to present itself either as having a 32-bit BAR or a 64-bit BAR.  We sell
our boards together with a miniature screw driver so users can make the
adjustment themselves.