We are on Shipometer 23.04 now. Shipometer 23.03 is a failure, for perhaps multiple reasons.
First, the shipometer is a HAT for a Raspberry Pi that can carry a ZED-F9R GPS+IMU, a BME280 pressure/temperature/humidity sensor, and an ICM20948 9DoF sensor. Even though the GPS+IMU has an IMU built into it, I want the ICM20948 because I can control it at a lower level, and because it has a magnetometer in it as well.
Finally, it carries an LPC210x as a precision timer. The ZED-F9R generates a pulse-per-second (PPS) which is accurately timed to have its rising edge right at the top of each second, with sub-microsecond accuracy. This PPS is routed to and captured by the Pi, but is also routed to the timer capture input of the LPC210x. This microprocessor is an old ARM7TDMI, but has a hardware 32-bit timer capable at running at 60MHz, with multiple usable capture inputs. The LPC210x is programmed to count at 60MHz, reset after 3.6 billion cycles, capture several inputs, and output the exact timer count of each pulse to its serial port, which is wired to the Pi UART1. This way, the time of each PPS and sensor data-ready signal can be recorded with no latency due to things like interrupts and real-time software.
