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Re: [Qemu-ppc] [Qemu-devel] [PATCH 2/2] m48t59: add mem_base value to m4

From: Maciej W. Rozycki
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH 2/2] m48t59: add mem_base value to m48t59_init_isa()
Date: Mon, 19 Jan 2015 18:17:34 +0000 (GMT)
User-agent: Alpine 2.11 (LFD 23 2013-08-11)

On Mon, 19 Jan 2015, Paolo Bonzini wrote:

> >> The reason I asked is simply because ISA devices never do MMIO (apart
> >> for the VGA window).
> > 
> > You mean in the QEMU world? At least physical SCSI and Ethernet
> > adapters had a MMIO space for the onboard ROM.
> Uh right, ROMs count as MMIO too.

 Some ISA Ethernet cards also used MMIO for r/w access, probably to get at 
packet memory more efficiently (I don't remember the details offhand) as 
port I/O transactions were notoriously slow; in any case this is where the 
"Memory" field printed by `ifconfig' under Linux comes from.  I'm sure 
there was other ISA equipment too using MMIO for one purpose or another.

 On a PC/AT class x86 computer these resources would normally be allocated 
somehow to the memory space in the 0xd0000-0xeffff range, to work with 
real-mode software.  With "somehow" usually meaning jumpers, though newer 
cards may have had DOS configuration software available to set it up, in a 
similar manner to how ECU configured port I/O and MMIO resources for EISA 

 BTW there were ISA DRAM expansion cards in existence too.


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