spi_sensor_reader

C++ SPI reader → POSIX shared memory (seqlock) → Python reader
~200 Hz sampling of strain gauges, power, and motor data.

Use this library to continuously poll sensor data and read it easily in Python.

Script should be continuously updated hook up more sensors.

Python Data Structure

{
    "seq": int,               # read_snapshot()[0]
    "power": {
        "ts": int,            # read_snapshot()[1][0]
        "current": float,     # read_snapshot()[1][1]
        "voltage": float,     # read_snapshot()[1][2]
    },
    "motor": {
        "ts": int,            # read_snapshot()[1][3]
        "throttle": float,    # read_snapshot()[1][4]
        "velocity": float,    # read_snapshot()[1][5]
    },
    "rpm_front": {
        "ts": int,            # read_snapshot()[1][6]
        "rpm_left": float,    # read_snapshot()[1][7]
        "rpm_right": float,   # read_snapshot()[1][8]
    },
    "rpm_back": {
        "ts": int,            # read_snapshot()[1][9]
        "rpm_left": float,    # read_snapshot()[1][10]
        "rpm_right": float,   # read_snapshot()[1][11]
    },
}

Quick Start

1. Compile & run the C++ writerBash

   g++ -O2 -std=c++17 spi_shm.cpp \
      -lpigpiod_if2 -lrt -pthread \
      -o spi_writer
   
   ./spi_writer

   (keep this running in one terminal — Ctrl+C to stop cleanly)

2. Read sensor data in Python

   Use the class in your own code. See main in read_shm.py for reference, or

   from read_shm import SensorShmReader
   import time
   
   reader = SensorShmReader()
   
   try:
       while True:
           snap = reader.read_snapshot() # or read_snapshot_dict(), but that's more overhead
           if snap:
               # Do whatever you want with the data
           time.sleep(0.005)  # ~200 Hz
   finally:
       reader.close()

Hardware

Current SPI setup (for Electrical reference):

CS GPIO	Description	Format
22	Power Monitor	u32 ts + float current + float voltage
23	Motor Controller	u32 ts + float throttle + float velocity
24	Front RPM	u32 ts + float rpm_left + float rpm_right
25	Back RPM	u32 ts + float rpm_left + float rpm_right

Bus: /dev/spidev0.0