pyserial实现Ymodem协议的代码

以下是使用pyserial实现Ymodem协议的代码示例：

import serial
import time


class Ymodem(object):
    """
    Ymodem protocol implementation using pyserial
    """

    # Ymodem constants
    SOH = chr(0x01)
    STX = chr(0x02)
    EOT = chr(0x04)
    ACK = chr(0x06)
    NAK = chr(0x15)
    CAN = chr(0x18)
    CRC = 'C'
    ABORT1 = chr(0x41)
    ABORT2 = chr(0x61)
    ABORT_COUNT = 10

    def __init__(self, port, baudrate, timeout=1):
        self.port = port
        self.baudrate = baudrate
        self.timeout = timeout
        self.serial = serial.Serial(port, baudrate, timeout=timeout)

    def send(self, filename):
        # Wait for C to signal start of transfer
        self.serial.timeout = 0.1
        while True:
            self.serial.write(self.CRC)
            response = self.serial.read(1)
            if response == self.CRC:
                break
        self.serial.timeout = self.timeout

        # Send filename and file size
        filesize = str(os.path.getsize(filename))
        filename = os.path.basename(filename)
        payload = filename + '\0' + filesize + ' '
        payload += ' ' * (128 - len(payload))
        self._send_packet(payload, 0)

        # Send file data
        with open(filename, 'rb') as f:
            block_num = 1
            while True:
                data = f.read(1024)
                if not data:
                    break
                self._send_packet(data, block_num)
                block_num += 1

        # Send EOT to signal end of transfer
        self.serial.write(self.EOT)
        response = self.serial.read(1)
        if response != self.ACK:
            raise Exception('ACK not received after EOT')

    def receive(self):
        # Wait for start of transfer signal
        response = None
        while response not in [self.CRC, self.ABORT1, self.ABORT2]:
            response = self.serial.read(1)
            if not response:
                continue
            if response == self.ABORT1 or response == self.ABORT2:
                self.serial.write(self.ACK)
                raise Exception('Transfer aborted')

        # Send C to signal start of transfer
        self.serial.write(self.CRC)

        # Receive filename and file size
        filename = ''
        filesize = ''
        while True:
            packet = self._read_packet()
            if packet is None:
                continue
            if packet[0] == chr(0):
                filename = packet[1:].split('\0')[0]
                filesize = int(packet[len(filename) + 2:])
                break

        # Receive file data
        with open(filename, 'wb') as f:
            block_num = 1
            while True:
                packet = self._read_packet()
                if packet is None:
                    continue
                if packet[0] == self.EOT:
                    self.serial.write(self.ACK)
                    break
                if packet[0] != chr(block_num % 256):
                    self.serial.write(self.NAK)
                    continue
                f.write(packet[1:])
                block_num += 1
                self.serial.write(self.ACK)

        return filename, filesize

    def _send_packet(self, data, block_num):
        if len(data) == 128:
            packet = self.SOH + chr(block_num % 256) + chr(255 - block_num % 256) + data
        else:
            packet = self.STX + chr(block_num % 256) + chr(255 - block_num % 256) + data + (' ' * (128 - len(data)))
        attempts = 0
        while attempts < self.ABORT_COUNT:
            self.serial.write(packet)
            response = self.serial.read(1)
            if response == self.ACK:
                break
            elif response == self.NAK:
                attempts += 1
            else:
                raise Exception('Invalid response from receiver')

    def _read_packet(self):
        packet = None
        while not packet:
            response = self.serial.read(1)
            if not response:
                continue
            if response == self.CAN:
                raise Exception('Transfer cancelled by receiver')
            if response == self.ABORT1 or response == self.ABORT2:
                self.serial.write(self.ACK)
                raise Exception('Transfer aborted')
            if response == self.STX or response == self.SOH:
                block_num = ord(self.serial.read(1))
                block_num += 256 - ord(self.serial.read(1))
                data = self.serial.read(128 if response == self.SOH else 1024)
                crc = self.serial.read(2)
                if self._calculate_crc(data) == crc:
                    self.serial.write(self.ACK)
                    packet = chr(block_num) + data
                else:
                    self.serial.write(self.NAK)
        return packet

    @staticmethod
    def _calculate_crc(data):
        crc = 0
        for byte in data:
            crc = crc ^ ord(byte)
            for i in range(8):
                if crc & 0x01:
                    crc = (crc >> 1) ^ 0x8C
                else:
                    crc >>= 1
        return chr(crc & 0xFF) + chr((crc >> 8) & 0xFF)

在使用时，可以创建一个Ymodem对象，并调用send()方法发送文件或调用receive()方法接收文件。例如：

ymodem = Ymodem('/dev/ttyUSB0', 115200)
ymodem.send('file.txt')

或者：

ymodem = Ymodem('/dev/ttyUSB0', 115200)
filename, filesize = ymodem.receive()