[flashrom] Hardware Sequencing vs Software Sequencing

john warwick btwvolcano at live.com
Tue Mar 30 07:42:27 CEST 2010


I was looking at Intel ICH SPI specs, and saw that there are a few registers on hardware sequencing. I was hence thinking on the feasibility of hardware sequencing. 

But then I saw that for hardware sequencing, I cannot find any registers where I can input opcodes like reading/writing to status registers. This is unlike software sequencing, where there is actually pre-op (06h) and other opcodes like 01h (writing status register) and 05h (reading status register).

So I was thinking if the host CPU/Bios Master can actually still do flashing of the Bios itself using hardware sequencing, without the need of pre-op such as 06h?


> Date: Tue, 30 Mar 2010 03:19:00 +0200
> From: c-d.hailfinger.devel.2006 at gmx.net
> To: btwvolcano at live.com
> CC: flashrom at flashrom.org
> Subject: Re: [flashrom] Hardware Sequencing vs Software Sequencing
> Hi John,
> On 30.03.2010 02:47, john warwick wrote:
> > I was looking through the code, and see that flashrom is using software sequencing. Is there any reason for software sequencing to be chosen instead of hardware sequencing?
> >   
> Assuming that you're talking about the Intel ICH SPI code, here's the
> info I have:
> Yes, there are multiple reasons why hardware sequencing is not supported:
> - You can't reflash the complete chip, just the region for the current
> (BIOS) descriptor.
> - You're unable to read the whole chip.
> - If you exchange the flash chip, write/erase may fail in random ways.
> - Crossflashing/hotflashing is pretty much impossible.
> - Nobody implemented it.
> > Are there any restrictions imposed for hardware sequencing?
> >   
> Please see above.
> Of course, if you're willing to contribute code for ICH SPI hardware
> sequencing, we'll be glad to review and merge it. Please be warned that
> this is a rather difficult task, especially because flashrom assumes
> that a flash chip can be accessed in full and you'll either have to
> emulate this or change flashrom safety checks and code flow in a few
> strategic places.
> Regards,
> Carl-Daniel
> -- 
> http://www.hailfinger.org/
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