HMI_Listener.py

#!/usr/bin/env python3
"""
Listen to the HMI to figure out what registers it wants to initialize.
based on OnTheLine arduino code.
"""
import socket
import argparse

HOST = "0.0.0.0"
PORT = 2101


def xor_bcc(data):
    b = 0
    for c in data:
        b ^= c
    return b


def read_d(addr):
    if addr == 570:
        return 26

    if addr in (3498, 3499, 3500):
        return 0

    return 0


def make_reply(addr, nbytes):
    words = nbytes // 2

    payload = b"\x06"          # ACK
    payload += b"000"          # device=00, status=0

    for i in range(words):
        payload += f"{read_d(addr+i):04X}".encode()

    bcc = xor_bcc(payload)
    payload += f"{bcc:02X}".encode()
    payload += b"\r"

    return payload


def handle(sock):

    buf = b""

    while True:

        c = sock.recv(1)
        if not c:
            break

        buf += c

        if c != b"\r":
            continue

        #print("RX:", buf)
        print("RX HEX:  ", " ".join(f"{b:02X}" for b in buf))
        print("RX ASCII:", repr(buf))


        if len(buf) >= 14 and buf[0] == 0x05:

            cmd = buf[4:6]

            if cmd == b"RD":

                addr = int(buf[6:10])
                nbytes = int(buf[10:12], 16)

                print(f"READ D{addr} ({nbytes//2} words)")

                reply = make_reply(addr, nbytes)

                print("TX:", reply)

                sock.sendall(reply)

            else:
                print("Unhandled command:", cmd)

        buf = b""


def main():

    ap = argparse.ArgumentParser()

    ap.add_argument("--host", default=HOST)
    ap.add_argument("--port", default=PORT, type=int)

    args = ap.parse_args()

    s = socket.socket()
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind((args.host, args.port))
    s.listen(1)

    print(f"Listening on {args.host}:{args.port}")

    while True:

        c, a = s.accept()

        print("Connected:", a)

        try:
            handle(c)
        finally:
            c.close()
            print("Disconnected")


if __name__ == "__main__":
    main()