LM6S3TR device FIFO pattern incorrect

[someguy42]

Hi there!

I'm having issues with my LSM6DS3TR device FIFO. I am trying to read and process all values stored in the FIFO by the accelerometer every interval using I2C. I am doing this by:

1) Retrieving number of unread messages in FIFO at addresses 3Ah and 3Bh.
2) For every unread message:

2.1) Reading the pattern in address 3Ch and 3Dh.
2.2) Reading the value of the FIFO in addresses 3Eh and 3Fh.
2.3) Processing and storing value retrieved from value as x, y or z axis.

 

I assume the pattern will tell me which axis the FIFO value relates to? I am only using the accelerometer, so I assume pattern = 0 is x axis, 1 is y axis and 2 is z axis? However, the pattern seems to be corrupted when I leave the program running long enough and will no longer align with the axis; for example- sometimes it will show pattern 0 but the value will be for y or z axis, pattern 1 but the value is for the x or z... etc...

Further details about the settings of the LSM6DS3TR device:
- I am using only the Accelerometer.
- The FIFO mode is set to continuous and ODR is set to 104Hz.
- The accelerometer ODR is set to 104Hz with no decimation.
- The BDU and IF_INC bits are set to 1 in CTRL3_C.

Does anyone possibly have a solution to this? Thanks in advance.

[Federica Bossi]

Hi @someguy42 ,

Once the FIFO is empty, data must not be retrieved from the FIFO_DATA_OUT_L and FIFO_DATA_OUT_H
registers.
It is recommended to read faster than 1*ODR at least three times the number of the enabled FIFO data set in
order to free FIFO slots for the new data: this allows avoiding loss of data.

[someguy42]

Hi @Federica Bossi ,

Thanks for your reply. However, I'm still a bit confused by what you mean? In my algorithm, I have obtained the number of unread messages and will only keep reading the FIFO buffer that number of times. That means there should be data in the FIFO still when I read the buffer. Anyway, I added a check for the FIFO_EMPTY bit in address 3Bh, but this does not fix the issue.

Regarding the FIFO read rate, I am reading at a sufficient speed. However, should this not matter if the FIFO is in continuous mode since the old data will just be replaced by new data? For my implementation, I don't mind some data loss.