[ECOS] Reset ARM while preserving memory, continue execution later

Heiko Panther heiko.panther@web.de
Thu Sep 30 10:46:00 GMT 2004

I'm running eCos on an ARM-based SOC target, and I need to save energy. The only way to make the ARM consume less power is to put it into reset (clocking it down is not possible here). 

So what I'd like to try out is putting the ARM into reset, and deasserting the reset after a short time (5ms). This is possible with external logic that I have.

I verified that the ARM resets and comes out of reset correctly. What I need now is a way to get eCos back to where it left off. The ARM's memory is conserved, so I have everything in the same condition as when the reset was asserted, except for the processor state. 

What would I need to do?

Before going into reset:
Disable interrupts
Save the processor state in a fixed location. 
Check flag to make sure we're not coming out of reset right now (see below).
if we're going into reset:
    Set a flag indicating that reset is being done.
    Do the reset.
else if we're coming from reset:
    Alter the flag.
    Enable interrupts.

When coming out of the reset:
Check the flag.
If power-saving reset is detected:
Alter flag (so coming back into the old state won't go into reset again).
Restore the processor state (execution continues above)

What do you think about this? Any suggestions? How would this fit in with the existing ARM arch code?


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