Re: steering the BE# ?

["John R Pierce" <pierce@scruznet.com>]

> From: Rafiki Kim Hofmans <tw38966@is1.bfu.vub.ac.be>
> To: Mailing List Recipients <pci-sig-request@znyx.com>
> Subject: steering the BE# ?
> Date: Saturday, August 17, 1996 3:51 PM
> 
> Hi,
> 
> how can I steer the BE# ?
> 
> e.g for a target-only device :
> 
> Suppose I want to do a write a byte to targetaddress (Base address +
> 0001)  with IO mapped IO. 
> How can I set the BE#, can it be done through software ?

Just do a _outp(Base+1, data); or mov dx,base+1 ; out dx,al

 
> Suppose I want to write a double word to targetaddress (Base address +
> 0011) with IO mapped IO, what happens with the BE# ?

Um, dword writes must be to dword aligned boundarys.  If you were to do a
<out dx,eax> to a odd address like base+0x0011, the CPU would probably do a
byte write to 0011, a word write to 0012, and a byte write to 0014... [i
don't -think- a intel processor bridge would do a 3 byte write to 0011

 
> And in case of a memory mapped IO write to the same address, what happens
> with AD1 and AD0 ?

Same as any other memory cycle...  No difference between memory mapped IO
and memory mapped memory except the IO is more likely to be tagged
non-prefetchable and non-cacheable.

-jrp
G
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