About JayBird

Hi there, We are experiencing a constant yet hardware-variable error on the timing of our watermark interrupt. We have set the ODR to 50Hz and would expect an interrupt every 1.28s for a constant readout of 64 frames. We have checked this on multiple PCBA's. On one board the interrupt comes constantly at 1.26s, on another board at 1.29s with exactly the same firmware build. This instead of the expected 1.28s. This was measured with a logic analyzer. We have checked the available samples in the FIFO, and this is constant for each hardware implementation at 64 frames. We are using the Bosch reference code. We are using the protocol as described in https://community.bosch-sensortec.com/t5/Knowledge-base/BMI160-FIFO-Advanced-Usage/ta-p/8957 We currently think it might be related to the clock calibration of the IMU. Yet, at 50Hz this error of ±2% seems quite high. We can not find how the clock on the IMU is calibrated, and hence don't know if this an inherent issue on the IMU's themselves or a synchronization error on e.g. the I2C clock coming from the MCU? Below you can see the hardware with a 1.29s WM interrupt cycle. Below you can see the hardware with a 1.26s WM interrupt cycle.   We have also performed "tap testing" on a regular interval (1min) and we can clearly see a constant offset error for each device, yet different for each device. device1.txt ----------- Time between taps in seconds: [60.6 60.24 60.44 60.36] Total time in seconds: 241.64 Total error in seconds: 1.64       device2.txt ----------- Time between taps in seconds: [59.2 58.86 59.06 58.98] Total time in seconds: 236.1 Total error in seconds: -3.9       device3.txt ----------- Time between taps in seconds: [59.46 59.1 59.3 59.22] Total time in seconds: 237.08 Total error in seconds: -2.92       device4.txt ----------- Time between taps in seconds: [59.5 59.14 59.36 59.26] Total time in seconds: 237.26 Total error in seconds: -2.74       device5.txt ----------- Time between taps in seconds: [60. 59.6 59.84 59.74] Total time in seconds: 239.18 Total error in seconds: -0.82     Is there a way to recalibrate the clock on the IMU? Or is the variation we are seeing across boards (yet constant within every board, independent of e.g. battery voltage) related to something else? Many thanks, @BSTRobin for any help you can provide. J ... View more