LSM9DS1 FIFO behavior

[Stefano Th�risod]

Posted on June 28, 2017 at 12:38

Hi,

I'm having some problem using the LSM9DS1 FIFO...

My objective is to continuously acquire, without loosing samples, the Gyro and Accelleration data. (The magnetometer is turned off)

This is what I do:

- I set the watermark threshold to 21 samples (IMU_FIFO_samples = 21 

(IMU_FIFO_samples = FlashBuffer_Initialize(IMU_6);)

- I configure the interrupt to be sent to pin INT1_A/G

(LSM9DS1_configInt(XG_INT1, INT_FTH, INT_ACTIVE_HIGH, INT_PUSH_PULL);)

- I configure the FIFO in Bypass Mode (LSM9DS1_setFIFO(FIFO_OFF, IMU_FIFO_samples);)

-

- In order to start the data acquisition I configure the FIFO in Continous Mode (LSM9DS1_setFIFO(FIFO_CONT, IMU_FIFO_samples);)

(I did try to set the IMU_SAMPLE_RATE to 14Hz and 900+Hz but the results are the same)

void IMU_Initialize(void)

{

uint16_t tst;

IMU_FIFO_samples = FlashBuffer_Initialize(IMU_6);

LSM9DS1_LSM9DS1(IMU_MODE_SPI, XGADDR, MADDR);

settings.accel.sampleRate = IMU_SAMPLE_RATE;

settings.gyro.sampleRate = IMU_SAMPLE_RATE;

settings.mag.operatingMode = 0x03; // Disabled

tst = LSM9DS1_begin();

LSM9DS1_enableBLE(true); // Big Little Indian

LSM9DS1_enableBDU(true); // Block Data Update

LSM9DS1_configInt(XG_INT1, INT_FTH, INT_ACTIVE_HIGH, INT_PUSH_PULL);

//LSM9DS1_setFIFO(FIFO_CONT, IMU_FIFO_samples);

LSM9DS1_enableFIFO(true);

__delay_ms(50);

LSM9DS1_setFIFO(FIFO_OFF, IMU_FIFO_samples);

}

uint8_t Acquisition_Start(void)

{ EX_INT2_InterruptFlagClear(); EX_INT2_InterruptEnable(); LSM9DS1_setFIFO(FIFO_CONT, IMU_FIFO_samples); return BT_OK;}

When the Interrupt is generated the following ISR is called

void Data_Acquisition_IMU(void)

{

...

// Read Data From IMU

//n5 = LSM9DS1_getFIFOSamples();

//n4 = LSM9DS1_getFIFOSamples();

//n3 = LSM9DS1_getFIFOSamples();

n = LSM9DS1_getFIFOSamples();

LSM9DS1_readAccelGyro_nAll(&FlashBufferIMU[ptr], IMU_FIFO_samples);

n1 = LSM9DS1_getFIFOSamples();

if(n1 > 31)

{

LSM9DS1_setFIFO(FIFO_OFF, IMU_FIFO_samples);

n3 = IMU_INT1_AG_GetValue();

n2 = LSM9DS1_getFIFOSamples();

EX_INT2_InterruptFlagClear();

n4 = LSM9DS1_getFIFOSamples();

LSM9DS1_setFIFO(FIFO_CONT, IMU_FIFO_samples);

}

...

}

++++ PROBLEMS ++++

Once in a while (quite often but not always) the block of data read from the FIFO is wrong (See attached picture)

LSM9DS1_readAccelGyro_nAll(&FlashBufferIMU[ptr], IMU_FIFO_samples);

void LSM9DS1_readAccelGyro_nAll(uint8_t *data, uint8_t n)

{

LSM9DS1_xgReadBytes(OUT_X_L_G, data, 12*n);

}

I read 12*21 = 252 bytes blocks from the FIFO and sometime the data look wrong (see attached picture)

The data should be always 0 but for az.

In order to debug the program I have been reading the number of data samples available in the FIFO when the ISR is called.

// Read Data From IMU

//n5 = LSM9DS1_getFIFOSamples(); //n4 = LSM9DS1_getFIFOSamples(); //n3 = LSM9DS1_getFIFOSamples(); n = LSM9DS1_getFIFOSamples();

Reading n5, n4, n3 and n I read inconsistent values

uint8_t LSM9DS1_getFIFOSamples(void)

{return (LSM9DS1_xgReadByte(FIFO_SRC) & 0x3F);}

Sometime n5 = 0 (even if the ISR should be called when in the FIFO there should be 21 samples) and immediately after I read n4 = 21 (the expected value)

--> WHY I READ n5 = 0 ???

 Sometime n5 = 21 but then I get n4 = 0x3F

--> The reported number of samples in the FIFO changes abruptly ???

Sometime  n5 = n4 = n3 = n = 21 and I read the FIFO data 

LSM9DS1_readAccelGyro_nAll(&FlashBufferIMU[ptr], IMU_FIFO_samples);

Sometime when I read the remaining samples in the FIFO, instead of reading 0, or at most a small number, I get 0x3F

Once I get 0x3F, in order to read meaningful number samples in the FIFO is to reset the FIFO setting the FIFO_OFF and the re-enabling it by setting FIFO_CONT

Any clue on how to fix it?

      Thank you

#fifo #lsm9ds1

[Stefano Th�risod]

Posted on June 28, 2017 at 16:34

Solved...

There was an interrupt conflict while communicating with the LSM9DS1