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DEV-958: use the ST datasheet accel sensitivity for the gen-2 LSM6DSV #288

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DEV-958: use the ST datasheet accel sensitivity for the gen-2 LSM6DSV #288

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fe367a5
DEV-958: use the ST datasheet accel sensitivity for the gen-2 LSM6DSV
marknolan Aug 20, 2026
aa61da1
DEV-958: correct the rationale - 0.061 mg/LSB is real, not a rounding
marknolan Aug 20, 2026
64ca844
DEV-958: clarify the class Javadoc sensitivity summary
marknolan Aug 20, 2026
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55 changes: 43 additions & 12 deletions ShimmerDriver/src/main/java/com/shimmerresearch/verisense/sensors/SensorLSM6DSV.java
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Expand Up @@ -41,11 +41,16 @@
* {@code VerisenseDevice.parseDataBlockDataLsm6dsv(...)}. This class provides the
* channel definitions, configuration and calibration.
* <p>
* Sensitivities: 32768/(FS*9.80665) LSB per m/s^2 for accel, the ST angular-rate
* spec of 4.375 mdps/LSB at +-125 dps for gyro, and 667 LSB/Gauss for the LIS2MDL
* mag - the last taken from {@link SensorLIS2MDL} rather than duplicated here, so
* calibrated magnetometer output is in GAUSS, consistent with every other Shimmer
* magnetometer and with the per-unit calibration the device stores.
* Sensitivities are the ST datasheet nominals throughout:
* <ul>
* <li>accel 0.061 / 0.122 / 0.244 / 0.488 mg/LSB for +-2 / 4 / 8 / 16 g;</li>
* <li>gyro 4.375 / 8.75 / 17.5 / 35 / 70 mdps/LSB for +-125 / 250 / 500 / 1000 /
* 2000 dps;</li>
* <li>LIS2MDL mag 667 LSB/Gauss.</li>
* </ul>
* The mag figure is taken from {@link SensorLIS2MDL} rather than duplicated here,
* so calibrated magnetometer output is in GAUSS, consistent with every other
* Shimmer magnetometer and with the per-unit calibration the device stores.
* <p>
* Default alignment is the real sensor->ASM frame map (accel/gyro share the chip
* mounting; the LIS2MDL frame is left-handed), matching the web SDK's
Expand Down Expand Up @@ -285,16 +290,42 @@ public static final class DatabaseConfigHandle {
* det +1 and computes canonical 0.0 entries, so it stays derived.) */
public static final double[][] DEFAULT_ALIGNMENT_LIS2MDL_MAG = {{1,0,0},{0,0,1},{0,1,0}};

// Accel sensitivity (LSB per m/s^2) = 32768/(FS_g*9.80665)
public static final double[][] SENS_ACCEL_2G = {{1670.703,0,0},{0,1670.703,0},{0,0,1670.703}};
public static final double[][] SENS_ACCEL_4G = {{835.3517,0,0},{0,835.3517,0},{0,0,835.3517}};
public static final double[][] SENS_ACCEL_8G = {{417.6759,0,0},{0,417.6759,0},{0,0,417.6759}};
public static final double[][] SENS_ACCEL_16G = {{208.8379,0,0},{0,208.8379,0},{0,0,208.8379}};
// Accel sensitivity (LSB per m/s^2) from the ST datasheet linear-acceleration
// sensitivity: 0.061 / 0.122 / 0.244 / 0.488 mg/LSB, i.e. 1/(mg_per_LSB/1000)/9.80665.
//
// These were previously derived as 32768/(FS_g*9.80665), on the assumption that
// the accel spans exactly the full 16-bit range at nominal full scale and that
// ST's printed figures were just that quantity rounded to three significant
// figures. They are not. The datasheet's own worked example (AN5922 Table 27,
// FS_XL = +-2 g) settles it: 1 g reads 0x4009 = 16393 LSB and 350 mg reads
// 0x1669 = 5737 LSB. 0.061 mg/LSB predicts 16393.4 and 5737.7; the 32768/FS
// derivation predicts 16384 and 5734.4. So the sensor really is 0.061 mg/LSB -
// full scale sits a little inside +-2 g - and the old derivation was wrong by
// 0.0576%, not merely a rounding apart from the datasheet.
//
// Same story as the gyro below, just with a much smaller margin: neither part
// maps its nominal full scale onto exactly 2^15 counts, so for both of them the
// ST mg/LSB and mdps/LSB figures are the authority and a 32768/FS derivation is
// simply incorrect. These values also match the firmware calibration seed
// (SC_ACCEL_SENS in asm_calibration.c), the web SDK catalog, the gen-1
// SensorLSM6DS3/SensorLIS2DW12 classes and ST's own reference driver
// (lsm6dsv_from_fs2_to_mg multiplies by 0.061f). Every example in
// STMems_Standard_C_drivers/lsm6dsv_STdC/examples converts through those
// helpers and none derives 32768/FS - including lsm6dsv_self_test.c, whose
// pass/fail limits are specified in mg, so ST's own self-test only comes out
// right if 0.122 mg/LSB is the true sensitivity.
public static final double[][] SENS_ACCEL_2G = {{1671.665922915,0,0},{0,1671.665922915,0},{0,0,1671.665922915}};
public static final double[][] SENS_ACCEL_4G = {{835.832961457,0,0},{0,835.832961457,0},{0,0,835.832961457}};
public static final double[][] SENS_ACCEL_8G = {{417.916480729,0,0},{0,417.916480729,0},{0,0,417.916480729}};
public static final double[][] SENS_ACCEL_16G = {{208.958240364,0,0},{0,208.958240364,0},{0,0,208.958240364}};

// Gyro sensitivity (LSB per dps) from the ST datasheet angular-rate sensitivity
// (4.375 mdps/LSB at +-125 dps, doubling per range) - the same spec/values as the
// gen-1 LSM6DS3. NOTE: the gyro does NOT span the full 16-bit range at its nominal
// full scale (unlike the accel), so a 32768/FS derivation is ~12.8% off.
// gen-1 LSM6DS3. NOTE: unlike the accel above, the gyro genuinely does NOT span
// the full 16-bit range at its nominal full scale - 4.375 mdps/LSB implies a real
// full scale of 143.4 dps for the +-125 dps setting, which is exactly where the
// part is observed to saturate - so here a 32768/FS derivation is not a rounding
// difference but plainly wrong (~14.7%).
public static final double[][] SENS_GYRO_125DPS = {{228.571428571,0,0},{0,228.571428571,0},{0,0,228.571428571}};
public static final double[][] SENS_GYRO_250DPS = {{114.285714286,0,0},{0,114.285714286,0},{0,0,114.285714286}};
public static final double[][] SENS_GYRO_500DPS = {{57.142857143,0,0},{0,57.142857143,0},{0,0,57.142857143}};
Expand Down
12 changes: 7 additions & 5 deletions .../test/java/com/shimmerresearch/verisense/API_00008_VerisenseLsm6dsvTaggedFifoParsing.java
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Expand Up @@ -142,14 +142,16 @@ public void test001_accelGyroMagInterleaved() throws Exception {
// CAL assertions - regression-locks the calibration constants against
// LITERAL expected values (the gyro sensitivity was ~12.8% wrong before the
// DEV-793 round-2 review fix; deriving the expectation from the class
// constants would defeat the lock). Defaults: accel +/-4 g = 835.3517
// LSB/(m/s^2); gyro +/-500 dps = 57.142857 LSB/dps (ST 17.50 mdps/LSB);
// constants would defeat the lock). Defaults: accel +/-4 g = 835.832961457
// LSB/(m/s^2) (ST 0.122 mg/LSB - see the sensitivity note in SensorLSM6DSV
// for why the datasheet figure is used and not the exact 32768/FS form);
// gyro +/-500 dps = 57.142857 LSB/dps (ST 17.50 mdps/LSB);
// mag 667 LSB/Gauss (LIS2MDL 1.5 mGauss/LSB, legacy rounding of 666.67).
// Since DEV-922 the defaults also apply the gen-2 sensor->ASM alignment:
// accel/gyro calibrated X/Y/Z come from raw Y/Z/X, mag X/Y/Z from raw X/Z/Y.
assertEquals(-200 / 835.3517, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_X), 0.0001);
assertEquals(300 / 835.3517, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_Y), 0.0001);
assertEquals(100 / 835.3517, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_Z), 0.0001);
assertEquals(-200 / 835.832961457, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_X), 0.0001);
assertEquals(300 / 835.832961457, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_Y), 0.0001);
assertEquals(100 / 835.832961457, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_ACC_Z), 0.0001);
assertEquals(-20 / 57.142857143, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_GYRO_X), 0.0001);
assertEquals(30 / 57.142857143, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_GYRO_Y), 0.0001);
assertEquals(10 / 57.142857143, cal(aligned0, SensorLSM6DSV.ObjectClusterSensorName.LSM6DSV_GYRO_Z), 0.0001);
Expand Down
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