diff options
| author | Bai Ping <b51503@freescale.com> | 2015-06-10 01:45:17 +0800 |
|---|---|---|
| committer | Bai Ping <b51503@freescale.com> | 2015-06-12 17:39:59 +0800 |
| commit | d40d224c1db101382b14753520aa3408715380e3 (patch) | |
| tree | c5ec525f493093380ef55c54a04cea032c44de81 | |
| parent | 439bb0179b48e543c5fe4b4dc75b0060677131cc (diff) | |
MLK-10828 thermal: imx: update the temperature calibration data for i.mx6
According to the design team:
After a thorough accuracy study of the Temp sense circuit,we found that
with our current equation, an average part can read 7 degrees lower than
a known forced temperature. We also found out that the standard variance
was around 2C; which is the tightest distribution that we could create. We
need to change the temp sense equation to center the average
part around the target temperature.
Old Equation:
Temp = Troom,cal - slope*(Count measured - Count room fuse)
Where Troom,cal = 25C and Slope = 0.4297157 - (0.0015974 * Count room fuse)
New Equation:
Temp = Troom,cal - slope*(Count measured - Count room fuse) +offset
Where Troom,cal = 25C and Slope = 0.4148468 - (0.0015423 * Count room fuse)
Offset = 3.580661
Signed-off-by: Bai Ping <b51503@freescale.com>
| -rw-r--r-- | drivers/thermal/imx_thermal.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c index a5e72d7ac996..eb5fe5795308 100644 --- a/drivers/thermal/imx_thermal.c +++ b/drivers/thermal/imx_thermal.c @@ -75,8 +75,9 @@ enum imx_thermal_trip { #define IMX_PASSIVE_DELAY 1000 #define FACTOR0 10000000 -#define FACTOR1 15976 -#define FACTOR2 4297157 +#define FACTOR1 15423 +#define FACTOR2 4148468 +#define OFFSET 3580661 #define TEMPMON_V1 1 #define TEMPMON_V2 2 @@ -417,23 +418,26 @@ static int imx_get_sensor_data(struct platform_device *pdev) * Derived from linear interpolation: * slope = 0.4297157 - (0.0015976 * 25C fuse) * slope = (FACTOR2 - FACTOR1 * n1) / FACTOR0 + * offset = OFFSET / 1000000 * (Nmeas - n1) / (Tmeas - t1) = slope * We want to reduce this down to the minimum computation necessary * for each temperature read. Also, we want Tmeas in millicelsius * and we don't want to lose precision from integer division. So... - * Tmeas = (Nmeas - n1) / slope + t1 - * milli_Tmeas = 1000 * (Nmeas - n1) / slope + 1000 * t1 - * milli_Tmeas = -1000 * (n1 - Nmeas) / slope + 1000 * t1 + * Tmeas = (Nmeas - n1) / slope + t1 + offset + * milli_Tmeas = 1000 * (Nmeas - n1) / slope + 1000 * t1 + OFFSET / 1000 + * milli_Tmeas = -1000 * (n1 - Nmeas) / slope + 1000 * t1 + OFFSET /1000 * Let constant c1 = (-1000 / slope) - * milli_Tmeas = (n1 - Nmeas) * c1 + 1000 * t1 - * Let constant c2 = n1 *c1 + 1000 * t1 + * milli_Tmeas = (n1 - Nmeas) * c1 + 1000 * t1 + OFFSET / 1000 + * Let constant c2 = n1 *c1 + 1000 * t1 + OFFSET / 1000 * milli_Tmeas = c2 - Nmeas * c1 */ temp64 = FACTOR0; temp64 *= 1000; do_div(temp64, FACTOR1 * n1 - FACTOR2); data->c1 = temp64; - data->c2 = n1 * data->c1 + 1000 * t1; + temp64 = OFFSET; + do_div(temp64, 1000); + data->c2 = n1 * data->c1 + 1000 * t1 + temp64; /* * Set the default passive cooling trip point to IMX_TEMP_PASSIVE. |