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Re: Address Mapping

Thanks for the valuable info!

Pavel Peleska      Tel:   ++49-89-722-41253
Siemens AG         Fax:   ++49-89-722-28502
SN EBG1            Email: Pavel.Peleska@oen.siemens.de
Hofmannstr. 51
81359 Munich
Original Text
From C=DE/A=SMTP/DDA=ID/pierce(a)hogranch.com, on 28.01.1997 20:45:
> we build a Pentium embedded system with the system (memory) address 
> 1:1 to the pci address space. However the CPU can access the PCI Bus only 
> within a 128 MB window in the third giga byte address range. We will be 
> using peripherial controllers via PCI. All controllers that we have seen 
> far can map their registers anywhere in the 32 bit address space - so far 
> so good. However the PCI Spec. defines a BAR type bit(2:1)=01 where the 
> address has to be located below 1 MB.
> Which devices use this type of BAR? Can controllers with this type of BAR 
> be relevant in an embedded system (without PC operating system)?

Basically legacy devices that have memory apertures that need to be 
accessed in
PC-DOS real mode, between 0x000C8000 and 0x000EFFFF.  You probably don't 
to worry about this at all.
> Are there any systems which use different address mapping schemes that 
> (System address:PCI address)? 

Yes, I believe some of the 64bit workstations such as DEC Alpha systems map 
entire 4GB PCI space up 'high' in their 2^64 address space.  Also, some 
like Apple PowerMacs map the PCI space several times, one aperture 
and one with 'byte swapping'