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201211f2dc
The existing algorithm makes several assumptions for a particular thermistor circuit. This patch introduces a more generic version that can be used for multiple thermistors on a single board. The idea is to approximate a curve produced by solving for voltage measued by an ADC using the Steinhart-Hart equation. For a straight line one only needs two data points. For a steady curve data points can be distributed evenly. For the most part, though, data points should be provided after a significant change in slope. More data points give more accuracy at the expense of memory, and we mostly only care about accuracy in the range between "warm" and "too hot" so only a few data points should be used. BUG=chrome-os-partner:54818 BRANCH=none TEST=added unit test, needs real testing Change-Id: I046e61dbfd1e8c26c2a533777f222f5413938556 Signed-off-by: David Hendricks <dhendrix@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/344781 Reviewed-by: Shawn N <shawnn@chromium.org>
For an overview of the Embedded Controller firmware, refer to http://www.chromium.org/chromium-os/2014-firmware-summit For instructions on building from source, refer to http://www.chromium.org/chromium-os/ec-development/getting-started-building-ec-images-quickly