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Updating the fan speeds according to the manufacturer's specs. The fan vendor recommends that the minimum fan speed be a 20% duty cycle. Since the built-in fan controller has a tach-based feedback loop, I'm using the RPM value instead of the duty cycle (20% is 2286 RPM, according to the vendor). The vendor also wants a 30% duty cycle to start turning, but the built-in fan controller provides support for fast-start too. The controller's minimum fast-start duty cycle is 50%, but it also has a programmable number of revolutions that it will wait before backing off. Holding my ear down close to the fans while they start and stop, it seems that the minimum 2 revolution start period is sufficient and provides the least noise. Of course, since I've never had any problems starting the fans directly at 1000 RPM this noise is a little more noticeable than that. It's quite possible that the built-in controller is smart enough to make 1000 RPM work by bumping the duty cycle up until the fans turn even if the fans don't like it. BUG=chrome-os-partner:32892 BRANCH=ToT,samus TEST=manual Listen closely and run the EC console "faninfo" command to see the fans start and stop as the system boots and idles. Change-Id: I47c9e7cef3f9f4bd815a13032fe10234decd62ed Signed-off-by: Bill Richardson <wfrichar@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/224830 Reviewed-by: Randall Spangler <rspangler@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit