ADXL372 FIFO data error with long time reading

Question

Hello, 
 I am using the adxl372 to measure the x,y,z acc data, the initialization is normal. 
 and i get the data through the FIFO, here comes the problem. 
 I set FIFO samples num as 480 (0xE0, 160 samples for each axis)，set the watermark interrupt, in the interrupt callback function, 
 I read the FIFO data through SPI.(read 157 samples each time) 
 Everything is fine in the begining, but a little moment later, the data goes wrong, and then three axes data begin to swap. 
 As the picture shows below, 
 
 I don't know why this comes like this, the data swaps every time i read the fifo(157 samples). 
 
 Best regards.

ADIApproved · Answer

Thanks for the question. It looks like this is some timing-related issue with the internal FIFO architecture and we are currently investigating the potential root cause. In the meantime, I'd suggest to stream from data register to avoid this data misalignment issue.

user2022 · Answer

I know this is an old thread, but I had a very similar problem when I first started working with XYZ data in the FIFO. I don&rsquo;t know if it is this exact problem described in this thread but it certainly looks like it to me. In case it helps anyone, I&rsquo;m posting my solution here. 
 I configured the ADXL372 to stream at 6400Hz, set the watermark interrupt at 384 entries, started streaming and went to sleep waiting for the FIFO to fill. After each watermark interrupt, I would read the STATUS, STATUS2 and FIFO_ENTRIES registers. If everything was OK, I would then read FIFO_ENTRIES - 3 entries from the FIFO_DATA register to always leave a full sample set in the FIFO. I used a fairly regular vibration input for testing, and I noticed that periodically the axes would obviously swap/rotate (e.g. X->Z, Y->X, Z->Y). It turned out that when the swap occurred it would happen near a FIFO read boundary and usually several in a row if not every single one; (e.g. it happened about every 384 samples and if I reduced the watermark to 15 samples, the swap would occur in multiples of around 15 samples). After a lot of experimenting and debugging, the solution I found that finally worked was to calculate FIFO_ENTRIES MOD 3 and then subtract three samples from that value as the number of samples to read from the FIFO_DATA. This guaranteed that I would only read samples in multiples of three and never empty the FIFO. The problem completely stopped occurring with this change. I had previously been blindly using whatever was in the FIFO_ENTRIES register, which was sometimes not a multiple of three.

PdelCorro · Answer

Hi reuter187 , 
 sorry for the late reply. Please find attached an example that I put together for Arduino Zero. 
 I hope this helps, 
 Pablo. 4454.adxl372_example_FIFO_stream.zip

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ADXL372 FIFO data error with long time reading