[coreboot] [RFC] CMOS options

Stefan Reinauer stepan at coresystems.de
Sat Dec 12 14:30:01 CET 2009

On 12/11/09 8:39 PM, ron minnich wrote:
> On Wed, Dec 9, 2009 at 2:57 AM, Andrew Goodbody
> <andrew.goodbody at tadpole.com> wrote:
>> Luc Verhaegen wrote:
>>> We have 892 bytes to our disposal in cmos. We can reserve 128 for
>>> board/cmos versioning, and reserve even 256 for the bootloader, and still
>>> have 512bytes left for coreboot options, which is tons when bits are used
>>> properly and when strings are not used.
>> Most boards I have used have a maximum space of 256 bytes that includes the
>> RTC. Where does the extra come from?
> On much of my hardware, the most I can assume is 128 bytes -
> subtracting many bytes that are weirdly hardware controlled (such as
> date).
> Some of our hardware has 256 bytes.
> The io ports only support an 8-bit address I thought?

The ports 0x70/0x71 even only support 7 bits... The 8th bit is used for
NMI control.

Higher CMOS bytes can be accessed by 0x72/0x73, 0x74/0x75....

However, if you try to access the upper 128 bytes by setting the topmost
bit in 0x70 it will just look like the upper 128 byte are a mirror of
the lower 128 bytes.


coresystems GmbH • Brahmsstr. 16 • D-79104 Freiburg i. Br.
      Tel.: +49 761 7668825 • Fax: +49 761 7664613
Email: info at coresystems.dehttp://www.coresystems.de/
Registergericht: Amtsgericht Freiburg • HRB 7656
Geschäftsführer: Stefan Reinauer • Ust-IdNr.: DE245674866

More information about the coreboot mailing list