Re: [Qemu-devel] IDE busmaster DMA support

[Lennert Buytenhek]

On Fri, Sep 30, 2005 at 12:15:04PM +0200, GaLi wrote:

> In the IDE BusMaster DMA specification :
> 
> "The control registers for the controller are allocated via the
> devices Base Address register at offset 0x20 in PCI configuration
> space."
> 
> If I read the word at offset 0x20 in the PCI configuration space, I get 
> 0xc001. But if I boot qemu with a linux live-cd, it tells me that BM-DMA 
> is at 0xc000

If the least significant bit in a BAR is 1, it means that you're
dealing with I/O space (as opposed to memory space.)  For BARs
referencing I/O space, the upper 30 bits encode the address, and
for memory space BARs, the upper 28 bits encode the address.

So, 0xc001 means "I/O space BAR, base address 0xc000."


--L