Re: [LinuxBIOS] Normal vs. fallback images and CMOS

[Jonathan Sturges]

Thanks!
Let me turn the CMOS question around though.  If an embedded board does have a battery, is it possible that it's just for the TOD clock and not CMOS?  In other words, if an unknown board has a battery, how can I positively confirm the existence of the CMOS?
I've got two revisions of the same board, one with battery and one without.  They're Winterminal boards, so they don't necessarily need CMOS settings.

thanks,
Jonathan

----- Original Message ----
From: Stefan Reinauer 
To: Jonathan Sturges 
Cc: LinuxBIOS mailing list 
Sent: Saturday, October 6, 2007 1:18:27 PM
Subject: Re: [LinuxBIOS] Normal vs. fallback images and CMOS

* Jonathan Sturges  [071006 18:04]:
> Question.  If an embedded board has no battery backup, it should have
> no (usable) CMOS.  Therefore, is a "Normal" image required on such a
> system?  My understanding is that CMOS settings are required to force
> the Fallback image to boot, except in cases of an missing or corrupt
> Normal image.

It's rather the other way around. CMOS allows the Normal image to be
booted. So without CMOS you always boot the Fallback image. Which is
good, because Fallback uses the hardcoded default values for all
otherwise CMOS drives variables.

So just drop the Normal image.

Stefan

[LinuxBIOS] Normal vs. fallback images and CMOS

[Uwe Hermann]

On Sun, Oct 07, 2007 at 05:02:21PM -0700, Jonathan Sturges wrote:
> Thanks!
> Let me turn the CMOS question around though.  If an embedded board does have a battery, is it possible that it's just for the TOD clock and not CMOS?  In other words, if an unknown board has a battery, how can I positively confirm the existence of the CMOS?
> I've got two revisions of the same board, one with battery and one without.  They're Winterminal boards, so they don't necessarily need CMOS settings.

I'm just guessing, but maybe just try reading CMOS bytes and see
if it works? If it doesn't I guess junk or 0xff will be returned.

I used something like this:

#define RTC_PORT 0x70

/**
 * Read a byte from the specified CMOS address.
 * 
 * @param addr The CMOS address to read a byte from.
 * @return The byte at the given CMOS address.
 */
inline u8 cmos_read(u8 addr)
{
        outb(addr, RTC_PORT);
        return inb(RTC_PORT + 1);
}

Uwe.