UART Serial Read & Write to MP3 Player Doesn't Work

[deanhystad]

I could not follow the link, so this advise of the uninformed guessing type. I think 170 (0xAA) is a start of packet marker and that the packet ends with some sort of checksum. I am accepting that the play track command is 7 and the read status command is 1. I also accept that the read status command returns 3 bytes.

Instead of looping and peeking at the read buffer I would specify a read timeout when opening the serial port.

"""Sends a  message via serial & receives back information via serial."""

import serial
import time

PLAYING_DONE = bytearray([0, 0, 0])

def write_command(port, command):
    """Write command to serial port"""
    command = [170].extend(command)  # Command packet starts with 0xAA
    command.append(sum(command) % 256)  # Append checksum
    port.write(bytearray(command))

def read_status(port):
    """Read status?  Returns 3L bytearray"""
    write_command(port, [1, 0])
    return port.read(3)

def play_track(port, track_info):
    """Start playing track.  Track is??"""
    write_command(port, [7].extend(track_info))

ser = serial.Serial(
    '/dev/ttyS0',
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=1)  # 1 second timeout for read

play_track(ser, [2, 0, 4])  # Track info?
playing = None
while playing != PLAYING_DONE:
    time.sleep(1)
    playing = read_status(ser)
    print(f'Status = f{playing}')
ser.close()