I'm programming a sensor array composed of 12 VL53L1X ToF sensors, connected to an STM32F427 chip through a single I²C bus. Measurement and inter-measurement times are set to 30 and 40 milliseconds respectively across all sensors. Sensors are queried in a loop and data is sent to a host PC through a USART connection.
Sensors are queried in the following manner:
- Call VL53L1_GetMeasurementDataReady, is sensor is not ready then return last valid reading;
- Otherwise, call VL53L1_GetRangingMeasurementData to get the sensor reading, then VL53L1_ClearInterruptAndStartMeasurement to prepare for the next cycle.
At each loop cycle, all sensors are queried in the manner above, then the data collected from the sensors is encoded in a string and sent to the host.
I noticed that data throughput decreases dramatically as the number of queried sensors increase:
- If I query just one sensor, I can get readings at a frequency of over 20 Hz;
- With four sensors, I get around 11 Hz;
- Six sensors give me 7.6 Hz;
- And querying all twelve sensors result in a paltry 3.8 Hz.
I have confirmed that the bottleneck is neither in the microcontroller nor the data connection — if I bypass the sensors and just send random data I can easily get over 30 Hz throughput. This leads me to believe the problem lies in the I²C bus.
Other than distributing the sensors among the controller's I²C buses, is there anything I can do to increase data throughput?
