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If 2 interrupts happen at the same time, there is a chance that the nested interrupt will not call svc_handler when it needs to. In extreme cases this could lead to tasks not getting woken up when they're supposed to and watchdog resetting. The reason stuff worked was because there were enough other interrupts around to eventually call the scheduler and switch to the ready task. This change modifies the interrupt calls to not call the scheduler directly (because in nested interrupt situation this causes problems), but defer the call to scheduling until after the irq finishes by triggering a low priority interrupt which will for sure call svc_host at the end. The PendSV irq was used for this purpose. BUG=chrome-os-partner:36193 TEST=No more SPI errors caused by scheduler problems TEST=usleeps now are more accurate, they're guaranteed to not take forever now BRANCH=veyron Change-Id: I42acde6b3eb7be2540a0de9a8562dee2ea2be7ab Signed-off-by: Alexandru M Stan <amstan@chromium.org> Signed-off-by: Vincent Palatin <vpalatin@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/248902 Tested-by: Alec Berg <alecaberg@chromium.org> Reviewed-by: Alec Berg <alecaberg@chromium.org> Commit-Queue: Alec Berg <alecaberg@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit