[SeaBIOS] 5 basic features provided by CSM, which SeaBIOS does provide?

Stojsavljevic, Zoran zoran.stojsavljevic at intel.com
Mon Dec 21 13:57:33 CET 2015

Hello Kevin,

All Good with setting CSM ON for legacy support. You need it for 16 bit BIOSes, and for legacy OSes, such as WIN XP or WIN 7 and derivatives.

Here is the question I am wondering: What if I decide to bring FSP -> Coreboot -> SeaBIOS -> WIN 8.1 32. Do I really need SeaBIOS with option set to: CSM ON (I brought WIN 8.1 32  on CC2 with SeaBIOS and feature CSM ON)? In other words, can I bring WIN 8.1 32 on FSP -> Coreboot -> SeaBIOS with CSM OFF?

The same question for: FSP -> Coreboot -> SeaBIOS -> WIN 8.1 64? I guess, here is CSM ON mandatory. Am I correct?

Could I have a true 32 or 64 UEFI compliant OS on BSP: FSP -> Coreboot -> SeaBIOS -> UEFI OS sans/without CSM feature ON? The same one I have after bringing on UEFI 32/64 BIOS UEFI 32/64 OS (CSM is OFF always)?  

Thank you,

-----Original Message-----
From: Kevin O'Connor [mailto:kevin at koconnor.net] 
Sent: Saturday, December 19, 2015 2:39 AM
To: Stojsavljevic, Zoran
Cc: coreboot; seabios at seabios.org; Sun, Jiming
Subject: Re: [SeaBIOS] 5 basic features provided by CSM, which SeaBIOS does provide?

On Fri, Dec 18, 2015 at 08:43:37AM +0000, Stojsavljevic, Zoran wrote:
> Hello both lists, Jiming,
> There are 5 basic features, provided by CSM SeaBIOS payload, and I am 
> looking to list of these features.
> Could you, please, provide to me list of these features, and some 
> description, and/or pointer to these descriptions?

I don't fully understand your question.  One can build SeaBIOS as a Compatibility Support Module (CSM) for UEFI, and this has been tested with OVMF on virtual machines.  It's theoretically also possible to use it as a CSM on real hardware with a UEFI payload on coreboot, but to the best of my knowledge that has never been tested.  When SeaBIOS is used as a CSM module, it provides legacy 16bit BIOS support on UEFI machines to bootloaders and option roms that require that support.

The only link I have for SeaBIOS CSM is:


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