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>
Separate the bd99992gw ADC interface from the NCP15WB thermistor
adc-to-temp maths so that the thermistor can be used with various
other interfaces.
BUG=chrome-os-partner:44764
TEST=make buildall -j
Manual on Glados. Boot to S0, run "temps".
Verify that temperatures start around 28C and begin to increase after
system is powered-on for a long duration.
BRANCH=None
Change-Id: I3e72e9f390feebaac2440dbe722485f8d1cf8c56
Signed-off-by: Wonjoon Lee <woojoo.lee@samsung.com>
Reviewed-on: https://chromium-review.googlesource.com/296871
Reviewed-by: Shawn N <shawnn@chromium.org>
