check-hdmi-status

#!/bin/bash
#
# This script checks the status of the HDMI capture chip.
# It reports the status as output on stdout (either as 'true' or 'false').
#
# Note: the script only supports checking tc358743 capture chips, whose input
# is mapped to /dev/video0. This applies to e.g. Voyager 2a hardware products,
# but not necessarily to Community/Hobbyist configurations.

# Exit on unset variable.
set -u

# Exit on first error.
set -e

if (( "${EUID}" != 0 )); then
  >&2 echo 'This script requires root privileges.'
  >&2 echo 'Please re-run with sudo:'
  >&2 echo "  sudo $0 $*"
  >&2 exit 1
fi

print_help() {
  cat << EOF
Usage: ${0##*/} [--help | --power | --signal]

Options:
  --help      Display this help and exit.
  --power     Check whether a powered HDMI cable is connected to the capture
              chip. Note: this may not produce accurate results on Voyager 2a
              hardware (or earlier).
  --signal    Check whether the capture chip receives signal.
              (This implies that a powered HDMI cable is connected.)
EOF
}

readonly VIDEO_DEVICE='/dev/video0'

# Check hardware preconditions.
if ! [[ -e "${VIDEO_DEVICE}" ]]; then
  >&2 echo "Error: no video input device mapped to '${VIDEO_DEVICE}'."
  exit 1
fi

if ! grep -q 'dtoverlay=tc358743' /boot/config.txt; then
  >&2 echo 'Error: no tc358743 capture chip found.'
  exit 1
fi

# Parse command-line arguments.
if [[ $# -eq 0 ]]; then
  print_help
  exit 1
fi

while (( "$#" > 0 )); do
  case "$1" in
    --help)
      print_help
      exit
      ;;
    --power)
      if [[ -n "${ACTION:-}" ]]; then
         >&2 echo 'Error: please only specify one flag.'
         exit 1
      fi
      ACTION='power'
      shift
      ;;
    --signal)
      if [[ -n "${ACTION:-}" ]]; then
         >&2 echo 'Error: please only specify one flag.'
         exit 1
      fi
      ACTION='signal'
      shift
      ;;
    *)
      >&2 echo "Unknown option: $1"
      print_help >&2
      exit 1
      ;;
  esac
done

# Validate that ACTION is set.
if [[ -z "${ACTION:-}" ]]; then
  >&2 echo 'Error: please specify a valid flag.'
  print_help >&2
  exit 1
fi
readonly ACTION

# Check for power.
if [[ "${ACTION:-}" == 'power' ]]; then
  # The output of the '--get-ctrl power_present' command is either
  # 'power_present: 0' or 'power_present: 1'.
  # Note that on devices prior to Voyager 3, the behavior of this command may
  # be unexpected, as it can persistently report 'power_present: 1', even if
  # no powered HDMI cable is connected (anymore).
  OUTPUT="$(v4l2-ctl --device "${VIDEO_DEVICE}" --get-ctrl power_present)"
  readonly OUTPUT
  if [[ "${OUTPUT}" == 'power_present: 1' ]]; then
    echo 'true'
  else
    echo 'false'
  fi

# Check whether there is an active signal.
elif [[ "${ACTION:-}" == 'signal' ]]; then
  # If there is signal, the output of '--get-input' will look like so:
  #
  #    Video input : 0 (Camera 0: ok)
  #
  # Otherwise, the output will look like so:
  #
  #    Video input : 0 (Camera 0: no signal, no sync lock)
  #
  # For reference, the output is assembled here:
  # https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-ctl/v4l2-ctl-io.cpp#n122
  OUTPUT="$(v4l2-ctl --device "${VIDEO_DEVICE}" --get-input)"
  readonly OUTPUT
  if [[ "${OUTPUT}" == *'(Camera 0: ok)'* ]]; then
    echo 'true'
  else
    echo 'false'
  fi

else
  print_help
  exit 1
fi