Reading from FIFO

[sjjackman]

Hello, I'm trying to program the LSM9DS1 to use FIFO mode, and then dump the FIFO onto my processor when it is full. In your code you say you use the FIFO but I'm unsure exactly how you do it. do you think you could quickly walk me through the procedure to read a full FIFO?

Your help is much appreciated.

[kriswiner]

Here is the relevant section where I use the FIFO:

 // Function which accumulates gyro and accelerometer data after device initialization. It calculates the average
// of the at-rest readings and then loads the resulting offsets into accelerometer and gyro bias registers.
 void accelgyrocalLSM9DS1(float * dest1, float * dest2)
 {  
   uint8_t data[6] = {0, 0, 0, 0, 0, 0};
   int32_t gyro_bias[3] = {0, 0, 0}, accel_bias[3] = {0, 0, 0};
   uint16_t samples, ii;

   // enable the 3-axes of the gyroscope
   writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG4, 0x38);
   // configure the gyroscope
   writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG1_G, Godr << 5 | Gscale << 3 |    Gbw);
   delay(200);
   // enable the three axes of the accelerometer 
 writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG5_XL, 0x38);
 // configure the accelerometer-specify bandwidth selection with Abw
 writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG6_XL, Aodr << 5 | Ascale << 3 | 0x04 |Abw);
 delay(200);
 // enable block data update, allow auto-increment during multiple byte read
 writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG8, 0x44);

  // First get gyro bias
  byte c = readByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG9);
  writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG9, c | 0x02);     // Enable gyro FIFO  
  delay(50);                                                       // Wait for change to take effect
  writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_FIFO_CTRL, 0x20 | 0x1F);  // Enable gyro FIFO stream mode and set watermark at 32 samples
  delay(1000);  // delay 1000 milliseconds to collect FIFO samples

  samples = (readByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_FIFO_SRC) & 0x2F); // Read number of stored samples

  for(ii = 0; ii < samples ; ii++) {            // Read the gyro data stored in the FIFO
 int16_t gyro_temp[3] = {0, 0, 0};
 readBytes(LSM9DS1XG_ADDRESS, LSM9DS1XG_OUT_X_L_G, 6, &data[0]);
 gyro_temp[0] = (int16_t) (((int16_t)data[1] << 8) | data[0]); // Form signed 16-bit integer for each sample in FIFO
 gyro_temp[1] = (int16_t) (((int16_t)data[3] << 8) | data[2]);
 gyro_temp[2] = (int16_t) (((int16_t)data[5] << 8) | data[4]);

 gyro_bias[0] += (int32_t) gyro_temp[0]; // Sum individual signed 16-bit biases to get accumulated signed 32-bit biases
 gyro_bias[1] += (int32_t) gyro_temp[1]; 
 gyro_bias[2] += (int32_t) gyro_temp[2]; 
 }  

gyro_bias[0] /= samples; // average the data
gyro_bias[1] /= samples; 
gyro_bias[2] /= samples; 

dest1[0] = (float)gyro_bias[0]*gRes;  // Properly scale the data to get deg/s
dest1[1] = (float)gyro_bias[1]*gRes;
dest1[2] = (float)gyro_bias[2]*gRes;

c = readByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG9);
writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_CTRL_REG9, c & ~0x02);   //Disable gyro FIFO  
delay(50);
writeByte(LSM9DS1XG_ADDRESS, LSM9DS1XG_FIFO_CTRL, 0x00);  // Enable gyro bypass mode

It is well commented and clear. Which parts are tripping you up?

[sjjackman]

Thanks for replying! So, you have to read the FIFO in a loop? I was trying to read it in one large block read. so if i understand correctly, once you read the top of the FIFO, it automatically pops the next value to the top to be read again? thanks again!