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When going into and waking from hibernation, we should keep CPU at high clock frequency so that we can save and restore chip state faster. This is especially true for the wake-up case as it affects AP boot time. This CL keeps the CPU at 12MHz for saving state and clocks it up to 48MHz for restoring. With this, the wake-up time (time from GPIO interrupt to completely restoring chip state) reduces from 11ms to 0.85ms. BUG=None TEST=Measure wake-up time with logic analyzer BRANCH=None Change-Id: Ib470a3d38959247b082cc7a5fd2d889cdc2a15ca Signed-off-by: Vic Yang <victoryang@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/206308 Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit