Raspberry Pi Bluetooth Watchdog / Reset

btreset.sh

#!/bin/sh

# Force a reset of the Bluetooth interface if it freezes up.
#
# https://github.com/raspberrypi/linux/issues/2832#issuecomment-597001597

if test $(id -u) -ne 0; then
  echo "This script must be run as root."
  exit 1
fi

killall hciattach
sleep 2
if grep -a Zero /proc/device-tree/model; then
  raspi-gpio set 45 op dl
  sleep 1
  raspi-gpio set 45 op dh
else
  /opt/vc/bin/vcmailbox 0x38041 8 8 128 0
  sleep 1
  /opt/vc/bin/vcmailbox 0x38041 8 8 128 1
fi
sleep 4
btuart

btwatchdog.service

[Unit]
Description=Montor and reset the Bluetooth interface if it dies

[Service]
Type=simple
ExecStart=/usr/local/bin/btwatchdog.sh

[Install]
WantedBy=multi-user.target

btwatchdog.sh

#!/usr/bin/env bash

# Monitor the Bluetooth clock for hiccups. If we see it act
# strangely (e.g. get stuck at 0 or jump by a large amount)
# for some reason, trigger a reset
#
# Relies on the presence of /usr/local/bin/btreset.sh
# May be run as a systemd service with btwatchdog.service

function gettime {
  printf "%d\n" $(hcitool clock | awk '/Clock/{print $2}')
}

function difftime {
  CLOCK_MAXIMUM=536870912
  OLD=$1
  NEW=$2

  DELTA=$((${2} - ${1}))
  if [[ ${DELTA} -lt 0 ]]; then
    DELTA=$((${DELTA} + ${CLOCK_MAXIMUM}))
  fi
  echo ${DELTA}
}

function clock2sec {
  CLOCK_RATE=3200
  TIME=$1

  echo $((${TIME} / ${CLOCK_RATE}))
}


SLEEP_SECONDS=10
FAIL_COUNT=0

TIME_NOW=$(gettime)
while true; do
  sleep ${SLEEP_SECONDS}
  TIME_OLD=${TIME_NOW}

  # Check how much time elapsed on the BT clock
  TIME_NOW=$(gettime)
  DELTA_T=$(difftime "${TIME_OLD}" "${TIME_NOW}")
  DELTA_S=$(clock2sec "${DELTA_T}")

  # If no time passed, something is wrong...
  if [[ "${DELTA_S}" -eq 0 || "${DELTA_S}" -gt $((2*${SLEEP_SECONDS})) ]]; then
    FAIL_COUNT=$((${FAIL_COUNT} + 1))
    echo "Encountered failure ${FAIL_COUNT}"
  elif [[ "${FAIL_COUNT}" -gt 0 ]]; then
    echo "Clock started back up. Resetting failure count."
    FAIL_COUNT=0
  fi

  # If we keep hitting failures, just reset the
  # device and hope it fixes itself.
  if [[ "${FAIL_COUNT}" -ge 5 ]]; then
    echo "Resetting device."
    /usr/local/bin/btreset.sh
    FAIL_COUNT=0
  fi
done