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Date: Wed, 13 Oct 2010 13:00:00 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: [SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to
	seabios
References: <4CB36A20.5020106@codemonkey.ws>	<20101011195955.GA5218@redhat.com>	<4CB373DD.50307@codemonkey.ws>	<4CB37E6E.8010106@zytor.com>	<20101012080124.GY2397@redhat.com>	<4CB48DCC.80804@zytor.com>	<20101012165658.GE5218@redhat.com>	<d732e51b-a79c-4cdd-8eb7-22c41d0b985f@email.android.com>	<20101012174121.GF5218@redhat.com>	<4CB49ED6.5000202@zytor.com>
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To: Gleb Natapov <gleb@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, seabios@seabios.org, qemu-devel@nongnu.org

On 10/13/2010 12:17 PM, H. Peter Anvin wrote:
> 
> The ACPI specification recognizes three interfaces as standard: PC/AT
> (64 bytes, even though 128 bytes is available on a lot of platforms),
> PIIX4 (256 bytes), and Dallas Semiconductor ("256 bytes or more").  The
> interface for the latter isn't well cited in the ACPI spec, but I'm
> guessing this is referring to the DS17885 series of chips, which can
> have up to 8K CMOS using a bank-switched scheme which presents 128 bytes
> at a time (thus accessible via only the standard 70/71 ports.)
> 

FWIW, the DS17885 scheme actually allows addressing up to 64K; 8K is the
maximum that DS produced with this particular interface as far as I
know, but there are 16 address bits available.

	-hpa