#!/bin/bash
#
# wake.sh -- wake the CAN bus by simulating a center-dash button press.
#
# Usage:
#   wake.sh
#
# Originally created: 01.2022 by jmccorm
# Last updated:       05.2026 (polish by magikh0e)
#
# WHAT IT DOES
#   Sends a Network Management (NM) wake frame on CAN-IHS that
#   mimics the press of a fictitious center-dash button. ECUs in
#   low-power state see traffic on $2D3 and bring themselves back
#   to operational, which makes the CAN bus carry traffic again so
#   other scripts (mute.sh, 3rd_brakelight.sh, etc.) have something
#   to read or write against.
#
# FRAME FORMAT
#   $2D3  07 00 00 00 00 00 00 X0
#
#   byte 0   = 0x07           NM frame type / source identifier
#   byte 1   = 0x00
#   byte 2   = 0x00           on a real button press, would be the
#                             button bitmap (0x01 = mute, etc.); 0x00
#                             here means "no button"
#   bytes 3-6 = 0x00
#   byte 7    high nibble = random 0..F per invocation
#             low  nibble = 0
#
#   The random high nibble of byte 7 keeps repeated wake calls from
#   looking identical to the BCM.  Without it, the BCM may interpret
#   N identical $2D3 frames in a row as a stuck button and either
#   filter them or trigger an error condition.  A fresh random value
#   on every call defeats that detection.
#
# REQUIRES
#   - can-utils (cansend)             apt install can-utils
#   - CAN-IHS up at 125 kbps          on can0 in this script
#
# WHO CALLS IT
#   - mute.sh uses an inlined copy of this logic in its
#     wake_bus() function (the polished version on this site dropped
#     the external dependency on /home/pi/bin/wake to stay
#     self-contained).
#   - Any script that needs the bus carrying traffic before its
#     candump listener has something to read can call this first.
#
# REVISION NOTES (2026-05-16)
#   - Added header explaining the frame format and the random-nibble
#     stuck-button-avoidance rationale (the original 2-line script
#     was correct but cryptic).

FAKE=$(printf "%x" $(( $RANDOM & 15 )))
cansend can0 2D3#07000000000000${FAKE}0