[support-gang] Real time clock battery during XO storage

Richard A. Smith richard at laptop.org
Mon Dec 9 22:04:28 EST 2013

On 12/09/2013 08:07 PM, James Cameron wrote:

> The symptom is that pressing the power button gives about a one second
> pulse on the power indicator, then it goes blank.  There is no serial
> cable output from the processor.

Take a look at the EC output.  It won't be as verbose as later 
generations but might provide some clues

> The laptop starts fine with the RTC oscillator stopped, provided it
> stopped because of removal of the RTC battery.  It just won't start if
> the RTC oscillator is stopped by writing to RTC control register.

Seems to me that this is may be some sort of OFW issue.  I seem to 
remember that we store some state in the RTC memory that is checked at 
early startup.  Just stopping the OSC would leave the memory as is (I 
think).  Perhaps that confuses OFW and its waiting for the something to 
respond that never will.

> Speculation: the XO-1 embedded controller is not detecting a 32 KHz
> signal from ball C8, GPIO27, or is not detecting some other normal
> response of the processor, and is abandoning the power up.

Nope.  Not for XO-1.  Thats the SCI# signal and its an output from the 
EC (and not used). Unlike 1.5 and beyond in XO-1 there is minimal 
feedback to the EC about the state of the CPU booting.  It's mostly just 
EC timers.  I won't say its impossible but I don't have any memory of 
anything like that and a quick look at the system power up code doesn't 
bring back an memories.

Richard A. Smith  <richard at laptop.org>
Former One Laptop per Child

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