Off-button reaction time

Bas Wijnen wijnen at
Wed Aug 17 13:02:13 EDT 2011

Andrea Bolognani schreef op wo 17-08-2011 om 12:17 [+0200]:
> Hold on a second: either I’m utterly mistaken, or the kernel is still far
> from being kicked in when the power button is pressed.

That is correct. But the delay is made by the rtc, which can be set up
when the kernel is running. It will retain its value as long as the rtc
has power (that is, when you remove the battery, you lose both the
current time and this setting).

>  I always assumed
> the circuitry needed that delay, and it was not avoidable.

It is avoidable, and I don't see a reason to use it.

> Are you telling me that I’ve been wrong the whole time, and that it is
> possible to achieve instant—boot making changes to the software only?

Yes. If the kernel sets the rtc register, it will instant-boot from then
on, until the power on the rtc goes down (which should never happen).

I propose to write the rtc register on every boot, so that even if the
battery was removed and the setting was lost, it still only results in
the delay once.

I'm talking about register HWFCR, page 131 of the programmer's manual.
Writing 0 to this register (0x10003024) will remove the delay.


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