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ADXL372 FIFO Issues

Question asked by NeerajSingla on Jan 2, 2018
Latest reply on Jan 10, 2018 by jwang

Hi

 

I played a little bit with the ADXL372 FIFO and i am stuck in few issues.

  I have setup FIFO to generate interrupt when it has more than 150 samples (i.e. set FIFO_SAMPLES to 0x96 for 50 3-axis samples).

 

1st Issue: As i am reading 50 complete sets of 3 axis data every-time, so i expect the second byte of the FIFO data to indicate the series start bit, but sometimes, i get the start indicator in the 2nd byte, sometime in 4th and sometimes in 6th. I believe the first sample should include the start byte as i start reading from the start byte and always read set of 3 samples. 

2nd Issue: Sometimes, out of 50 sample sets, only a first few samples would be good, rest would be just garbage data. Sometimes, all 150 samples are good, sometime 140 samples are good, sometimes just 10 samples are good and rest of the samples does not have Series Start Indicator, which confirms me that it is not real data.

 

3rd Issue: Sometime after getting the FIFO_FULL interrupt, when i read the FIFO_ENTRIES register, the register values are quite less instead of 150, like 30-40, whereas i would expect to get more than 150 samples. The next time, the interrupt comes really quickly, which also gives me a hint that the FIFO actually had more than 30-40 samples, but somehow FIFO_ENTRIES register returned smaller number.

 

4th Issue: When i read the STATUS Register, sometime i get 0x47 and sometime i get 0x44. 0x44 means that FIFO_RDY bit is zero, which means that the FIFO did not have any valid sample. But i am reading this register after FIFO_FULL interrupt has been raised and i was able to read all 150 samples, so FIFO_RDY bit being zero raises questions.

 

Please suggest, if you have any ideas to fix these issues.

 

Thanks,

Neeraj

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