AI-Deck Himax camera callback not called again if registered too quickly after last catpure

[Jool99]

How to reproduce:

• Call pi_camera_capture async()
• In callback function, call
  • pi_camera_control(&camera, PI_CAMERA_CMD_STOP, 0);
  • HERE (see below)
  • pi_camera_capture_async(&camera, cameraBuffer, CAM_WIDTH * CAM_HEIGHT, pi_task_callback(&task1, cam_handler, NULL));
  • pi_camera_control(&camera, PI_CAMERA_CMD_START, 0);

If there is not sufficient delay where it says HERE above, the callback function will not be called a second time.

If executing a sufficiently large CNN this might not be a problem but, weirdly, a delay is required.

For the exact setup, this issue was discovered in the AI Deck classification demo by bitcraze. The callback function discussed above corresponds to cam_handler in classification.c

This has previously been discussed here.