Writing a Camera Driver

Each camera chip supported by the core is an ImageSensor subclass in its own library. The OV5640 and VD66GY libraries are the two implementations. A new sensor is added by writing one class; no core changes are needed unless the sensor outputs a pixel format the core does not handle.

#Interface

class MySensor : public ImageSensor {
public:
  MySensor() { registerAsActive(1u); }       // 1 = physical CSI lanes, 2 = inverted

  int init(CameraResolutionN6 res, CameraFpsN6 fps, CameraMirrorFlipN6 flip,
           uint16_t &out_w, uint16_t &out_h) override {
    // reset, chip ID check, register tables, orientation, stream on, over I2C
    out_w = 640; out_h = 480;
    return 0;                                // 0 on success, negative on failure
  }

  uint32_t chipId() override { return 0x1234u; }

  void getFormat(SensorFormat &out) override {
    out.pixel_format = N6_PIXFMT_YUV422_YUYV;
    out.color_space  = N6_COLORSPACE_BT601;
  }

  void streamOn()  override {}
  void streamOff() override {}
  const char *name() override { return "MySensor"; }
};

MySensor camera;

Optional methods cover autofocus, strobe, exposure, gain and white balance, with controlCaps() reporting which are implemented.

#Registration

registerAsActive() records the object as the sensor Vision drives and publishes its CSI data lane mapping. The lane argument is a property of the carrier: 1 for the standard wiring, 2 for inverted lanes. Vision.begin() later calls init(), getFormat() and streamOn() on the registered object.

A sketch declares exactly one sensor object. Vision.setSensor() exists for choosing between several declared sensors at run time and is rarely needed.

#Format contract

getFormat() drives the whole DCMIPP pipeline: the CSI data type, the packer, the colour space conversion and the JPEG encoder configuration. Three formats are defined:

A sensor with a format not in this list requires a case added to n6_apply_sensor_format() in cores/NeuroN6/NeuroN6.c.

#I2C

Sensor control runs over I2C1, shared with the on-board sensors. A driver that calls the HAL directly brackets each transaction with n6_i2c_lock() and n6_i2c_unlock(). See I2C with Wire.

#Failure behaviour

If init() returns a negative value, Vision.begin() prints a console line naming the sensor and its expected chip ID, and Vision.run() returns early on every call rather than blocking in inference. A sketch with a missing or miswired camera therefore degrades to a diagnostic.

#References

The CustomSensor example, under File > Examples > OV5640, is a compilable skeleton. libraries/OV5640/src/OV5640_Sensor.cpp is a complete implementation with autofocus, strobe and capture controls. libraries/VD66GY/src/VD66GY_Sensor.cpp shows a raw Bayer sensor with an ISP.