Re: Why the & ?

[Jon M. T. <ta...@ec...>]

On Wed, 15 Nov 2000, Lee Brown wrote:

> 
> blade3D_io->mem.base_io   = blade3D->pci.BaseAddr0 & ~(BLADE3D_Base0_Size - 1);
> 
> Why isn't this just the pci.BaseAddr0?  I know there is a reason.
> Sorry if this is a stupid question.

	No, it is a very good question.  This is confusing if you haven't
dealt with it before.  The PCI BARs (Base Address Registers) do not
containt only the 24-bit base address of a PCI memory window.  The lower
two bits (for I/O devices) or four bits (for memory devices) contain
device type info which must be masked out to give a valid address.  I
assume that this is what is being done here.

Jon

---
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