LSM6DSV FSM example with baro (LPS22XX) as external sensor?

[KWine]

I have examined the FSM example folder on github and, while there is an example for an external magnetometer, I haven't found any examples for an external barometer. Is there such an example? And if so, where can I find it?

I believe I can create my own, but it is always easier to follow a previous working example. Thanks!

[Federica Bossi]

Hi @KWine ,

Where have you found the example on github? Can you share the link?

Thanks

[KWine]

https://github.com/STMicroelectronics/STMems_Finite_State_Machine

and specifically for the LSM6DSV,

https://github.com/STMicroelectronics/STMems_Finite_State_Machine/tree/master/application_examples/lsm6dsv

Very useful! But neither in the LSM6DSV nor any other (i.e., LSM6DSO) folder do I see an example for using external baro data. This would be a useful addition! Thanks.

[KWine]

A corollary question. I averaged ten baro samples at 1 Hz on start up to get:

15:17:43.812 -> reference Pressure = 973.6434 mBar
15:17:43.812 -> standard deviation = 0.0115 mBar
15:17:43.812 -> HF reference Pressure = 0x639B
15:17:43.812 -> FF reference Pressure = 973.5000 mBar

It looks like the half-precision result is only good to 0.5 mBar, but the difference in pressure I see when I raise the baro three feet off the table (a typical gesture motion) is about 0.1 mBar such that including baro data in the FIFO for FSM using Mode 2 seems rather hopeless.  

Nevermind, I see that only the sensitivity is to be entered in HFP format while the baro data is kept at full precision.

[KWine · Accepted solution]

Just an FYI, I got this to work. First I configured the baro registers on Emb Adv Features page 2 with the hPa/LSB sensitivity and an average of the power-on pressure as a reference:

    // set baro sensitivity and offset for FSM operations
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_RW,    0x40);                             // Enable page write
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_SEL,   0x21);                             // Select page 2 (bit 0 must always be 1)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_ADDR,  0x00);                             // Select EXT_FORMAT register
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x04);                             // select 3-byte format for barometer
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // set lower byte of baro sensitivity (1/4096 = 0x0C00 in HFP)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x0C);                             // set higher byte for baro sensitivity
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, (refPressure & 0x000000FF));       // set XL byte for baro offset
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, (refPressure & 0x0000FF00) >> 8);  // set L byte for baro offset
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, (refPressure & 0x00FF0000) >> 16); // set H byte for baro offset
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_SEL,   0x01);                             // Select page 0 (bit 0 must always be 1)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_RW,    0x00);                             // Disable page write

Then I adapted the ST motion detect FSM program to detect a 0.1 hPa pressue drop corresponding to a ~1 meter rise in altitude (so lift detect):

    // lift detect (threshold crossing) using barometer
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x51);                             // write to CONFIG_A (one threshold, one mask, one short timer)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to CONFIG_B
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x10);                             // write to SIZE (18 byte program)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to SETTINGS
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to RESET POINTER
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to PROGRAM POINTER
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x9A);                             // write to THRESH1 LSB
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x01);                             // write to THRESH1 MSB  (0x019A is 410 which means 0.1 mBar for barometer)
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x40);                             // write to MASKA  (-x axis) x-axis is pressure for barometer
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to TMASKA
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to TC
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x10);                             // write to TIMER3 (16 samples at 30 Hz = 0.53 seconds)
    
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x23);                             // write to SINMUX Set input multiplexer
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x02);                             // select external sensor
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x53);                             // write to GNTH1 | TI3
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x99);                             // write to OUTC
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x50);                             // write to GNTH1 | NOP
    _i2c_bus->writeByte(LSM6DSV_ADDRESS, LSM6DSV_PAGE_VALUE, 0x00);                             // write to STOP

I get a "lift detect" interrupt whenever the pressure drops by ~0.1 hPa, i.e., whenever I lift the sensor over my head.

Pretty cool!