mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2025-01-19 12:24:34 +08:00
iio:st_pressure: document sampling gains
Details scaling factors and offsets applied to raw temperature and pressure samples. Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com> Tested-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Gregor Boirie
Jonathan Cameron
parent
c9d5e5b97e
commit
19b7b8a89b
@ -28,6 +28,72 @@
|
||||
#include <linux/iio/common/st_sensors.h>
|
||||
#include "st_pressure.h"
|
||||
|
||||
/*
|
||||
* About determining pressure scaling factors
|
||||
* ------------------------------------------
|
||||
*
|
||||
* Datasheets specify typical pressure sensitivity so that pressure is computed
|
||||
* according to the following equation :
|
||||
* pressure[mBar] = raw / sensitivity
|
||||
* where :
|
||||
* raw the 24 bits long raw sampled pressure
|
||||
* sensitivity a scaling factor specified by the datasheet in LSB/mBar
|
||||
*
|
||||
* IIO ABI expects pressure to be expressed as kPascal, hence pressure should be
|
||||
* computed according to :
|
||||
* pressure[kPascal] = pressure[mBar] / 10
|
||||
* = raw / (sensitivity * 10) (1)
|
||||
*
|
||||
* Finally, st_press_read_raw() returns pressure scaling factor as an
|
||||
* IIO_VAL_INT_PLUS_NANO with a zero integral part and "gain" as decimal part.
|
||||
* Therefore, from (1), "gain" becomes :
|
||||
* gain = 10^9 / (sensitivity * 10)
|
||||
* = 10^8 / sensitivity
|
||||
*
|
||||
* About determining temperature scaling factors and offsets
|
||||
* ---------------------------------------------------------
|
||||
*
|
||||
* Datasheets specify typical temperature sensitivity and offset so that
|
||||
* temperature is computed according to the following equation :
|
||||
* temp[Celsius] = offset[Celsius] + (raw / sensitivity)
|
||||
* where :
|
||||
* raw the 16 bits long raw sampled temperature
|
||||
* offset a constant specified by the datasheet in degree Celsius
|
||||
* (sometimes zero)
|
||||
* sensitivity a scaling factor specified by the datasheet in LSB/Celsius
|
||||
*
|
||||
* IIO ABI expects temperature to be expressed as milli degree Celsius such as
|
||||
* user space should compute temperature according to :
|
||||
* temp[mCelsius] = temp[Celsius] * 10^3
|
||||
* = (offset[Celsius] + (raw / sensitivity)) * 10^3
|
||||
* = ((offset[Celsius] * sensitivity) + raw) *
|
||||
* (10^3 / sensitivity) (2)
|
||||
*
|
||||
* IIO ABI expects user space to apply offset and scaling factors to raw samples
|
||||
* according to :
|
||||
* temp[mCelsius] = (OFFSET + raw) * SCALE
|
||||
* where :
|
||||
* OFFSET an arbitrary constant exposed by device
|
||||
* SCALE an arbitrary scaling factor exposed by device
|
||||
*
|
||||
* Matching OFFSET and SCALE with members of (2) gives :
|
||||
* OFFSET = offset[Celsius] * sensitivity (3)
|
||||
* SCALE = 10^3 / sensitivity (4)
|
||||
*
|
||||
* st_press_read_raw() returns temperature scaling factor as an
|
||||
* IIO_VAL_FRACTIONAL with a 10^3 numerator and "gain2" as denominator.
|
||||
* Therefore, from (3), "gain2" becomes :
|
||||
* gain2 = sensitivity
|
||||
*
|
||||
* When declared within channel, i.e. for a non zero specified offset,
|
||||
* st_press_read_raw() will return the latter as an IIO_VAL_FRACTIONAL such as :
|
||||
* numerator = OFFSET * 10^3
|
||||
* denominator = 10^3
|
||||
* giving from (4):
|
||||
* numerator = offset[Celsius] * 10^3 * sensitivity
|
||||
* = offset[mCelsius] * gain2
|
||||
*/
|
||||
|
||||
#define MCELSIUS_PER_CELSIUS 1000
|
||||
|
||||
/* Default pressure sensitivity */
|
||||
@ -48,7 +114,11 @@
|
||||
#define ST_PRESS_1_OUT_XL_ADDR 0x28
|
||||
#define ST_TEMP_1_OUT_L_ADDR 0x2b
|
||||
|
||||
/* CUSTOM VALUES FOR LPS331AP SENSOR */
|
||||
/*
|
||||
* CUSTOM VALUES FOR LPS331AP SENSOR
|
||||
* See LPS331AP datasheet:
|
||||
* http://www2.st.com/resource/en/datasheet/lps331ap.pdf
|
||||
*/
|
||||
#define ST_PRESS_LPS331AP_WAI_EXP 0xbb
|
||||
#define ST_PRESS_LPS331AP_ODR_ADDR 0x20
|
||||
#define ST_PRESS_LPS331AP_ODR_MASK 0x70
|
||||
@ -71,7 +141,9 @@
|
||||
#define ST_PRESS_LPS331AP_OD_IRQ_MASK 0x40
|
||||
#define ST_PRESS_LPS331AP_MULTIREAD_BIT true
|
||||
|
||||
/* CUSTOM VALUES FOR LPS001WP SENSOR */
|
||||
/*
|
||||
* CUSTOM VALUES FOR THE OBSOLETE LPS001WP SENSOR
|
||||
*/
|
||||
|
||||
/* LPS001WP pressure resolution */
|
||||
#define ST_PRESS_LPS001WP_LSB_PER_MBAR 16UL
|
||||
@ -94,7 +166,11 @@
|
||||
#define ST_PRESS_LPS001WP_OUT_L_ADDR 0x28
|
||||
#define ST_TEMP_LPS001WP_OUT_L_ADDR 0x2a
|
||||
|
||||
/* CUSTOM VALUES FOR LPS25H SENSOR */
|
||||
/*
|
||||
* CUSTOM VALUES FOR LPS25H SENSOR
|
||||
* See LPS25H datasheet:
|
||||
* http://www2.st.com/resource/en/datasheet/lps25h.pdf
|
||||
*/
|
||||
#define ST_PRESS_LPS25H_WAI_EXP 0xbd
|
||||
#define ST_PRESS_LPS25H_ODR_ADDR 0x20
|
||||
#define ST_PRESS_LPS25H_ODR_MASK 0x70
|
||||
@ -117,7 +193,11 @@
|
||||
#define ST_PRESS_LPS25H_OUT_XL_ADDR 0x28
|
||||
#define ST_TEMP_LPS25H_OUT_L_ADDR 0x2b
|
||||
|
||||
/* CUSTOM VALUES FOR LPS22HB SENSOR */
|
||||
/*
|
||||
* CUSTOM VALUES FOR LPS22HB SENSOR
|
||||
* See LPS22HB datasheet:
|
||||
* http://www2.st.com/resource/en/datasheet/lps22hb.pdf
|
||||
*/
|
||||
#define ST_PRESS_LPS22HB_WAI_EXP 0xb1
|
||||
#define ST_PRESS_LPS22HB_ODR_ADDR 0x10
|
||||
#define ST_PRESS_LPS22HB_ODR_MASK 0x70
|
||||
@ -413,6 +493,10 @@ static const struct st_sensor_settings st_press_sensors_settings[] = {
|
||||
},
|
||||
.fs = {
|
||||
.fs_avl = {
|
||||
/*
|
||||
* Sensitivity values as defined in table 3 of
|
||||
* LPS22HB datasheet.
|
||||
*/
|
||||
[0] = {
|
||||
.num = ST_PRESS_FS_AVL_1260MB,
|
||||
.gain = ST_PRESS_KPASCAL_NANO_SCALE,
|
||||
|
||||
Loading…
Reference in New Issue
Block a user