Serial touchscreen protocol of some old shitty touchscreen terminal

protocol.py

#!/usr/bin/env python3

'''
standard message:

0x55 0x54 <action> <x lo> <x hi> <y lo> <y hi> 0xFF 0x00 <checksum>

actions:
 - 0x01 - touch down
 - 0x02 - touch hold
 - 0x04 - touch up
'''


import sys
import functools

fname = sys.argv[1]

actions = [
	'<invalid>',
	'DOWN',
	'HOLD',
	'<invalid>',
	'UP'
]

def hexdump(bytes):
	for byte in bytes:
		print('{:02x} '.format(byte), end='')
	print()

def humandump(bytes):
	if len(bytes) < 10:
		print("Partial packet with {} bytes: ".format(len(bytes)), end='')
		hexdump(bytes)
		return
	if len(bytes) > 10:
		print("Oversize packet with {} bytes: ".format(len(bytes)), end='')
		hexdump(bytes)
		return

	action = actions[bytes[2]]
	x = bytes[3] + bytes[4] * 256
	y = bytes[5] + bytes[6] * 256
	print("{} @({},{})".format(action, x, y))


data = b''
with open(fname, 'rb') as f:
	while True:
		data += f.read(20)
#		hexdump(data)
		sep = b'UT'
		touches = data.split(sep)
		data = touches[-1]
		touches = [ sep + touch for touch in touches[:-1] ]
		for touch in touches:
			humandump(touch)
#			hexdump(touch)
#			csum = (0xaa + functools.reduce(lambda acc, c: acc + c, touch[:-1], 0)) % 256
#			print('{:02x}'.format(csum))