SensorAccelFifo (UORB message) 
c
uint64 timestamp          # time since system start (microseconds)
uint64 timestamp_sample
uint32 device_id          # unique device ID for the sensor that does not change between power cycles
float32 dt                # delta time between samples (microseconds)
float32 scale
uint8 samples             # number of valid samples
int16[32] x               # acceleration in the FRD board frame X-axis in m/s^2
int16[32] y               # acceleration in the FRD board frame Y-axis in m/s^2
int16[32] z               # acceleration in the FRD board frame Z-axis in m/s^2