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Date: Thu, 10 Mar 2011 23:10:30 +0100
From: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
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Subject: Re: [Qemu-devel] RFC: emulation of system flash
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To: Jordan Justen <jljusten@gmail.com>
Cc: Gleb Natapov <gleb@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Michal Suchanek <hramrach@centrum.cz>, Kevin O'Connor <kevin@koconnor.net>, Avi Kivity <avi@redhat.com>

Auf 10.03.2011 22:55, Jordan Justen schrieb:
> On Thu, Mar 10, 2011 at 13:37, Carl-Daniel Hailfinger
> <c-d.hailfinger.devel.2006@gmx.net> wrote:
>   
>> Auf 10.03.2011 05:51, Jordan Justen schrieb:
>>     
>>> I have documented a simple flash-like device which I think could be
>>> useful for qemu/kvm in some cases.  (Particularly for allowing
>>> persistent UEFI non-volatile variables.)
>>>
>>> http://wiki.qemu.org/Features/System_Flash
>>>
>>> Let me know if you have any suggestions or concerns.
>>>
>>>       
>> Is there any reason why you chose to invent an interface for the flash
>> chip which is more complicated than the interface used by common flash
>> chips out there?
>> Maybe some EFI requirement?
>>     
> This is a simpler version than the flash devices I'm used to dealing
> with for x86/x86-64 UEFI systems.  Can you suggest an alternative real
> interface that is simpler?
>   

Pseudocode for the real interface most common on x86 before SPI came along:

Write a page (256 bytes) or a few bytes:
chip_writeb(0xAA, bios_base + 0x5555);
chip_writeb(0x55, bios_base + 0x2AAA);
chip_writeb(0xA0, bios_base + 0x5555);
chip_writeb(databyte0, bios_base + addr);
chip_writeb(databyte1, bios_base + addr + 1);
chip_writeb(databyte2, bios_base + addr + 2);
chip_writeb(databyte3, bios_base + addr + 3);
... up to 256 databytes.
chip_readb(bios_base);
The last chip_readb(bios_base) is repeated until the result does not
change anymore.

For me, that looks pretty simple and straightforward, especially
compared to other more exotic flash chip interfaces.

Regards,
Carl-Daniel

-- 
http://www.hailfinger.org/