使用pySerial连接FPV控制器COM口无数据返回问题求助

问题背景 #

使用pySerial库通过COM口访问FPV控制器时，连接看似成功，但发送命令后始终得不到响应。仅在BetaFlight CLI中执行命令并释放端口后，代码才能正常运行；但重新插拔USB后，问题复现。推测是代码无法触发控制器的唤醒机制，导致设备忽略命令。

初始代码 #

port = '/dev/cu.usbmodem0x80000001'
baudrate = 115200

import serial
import time

def read_vtxtable():
    try:
        ser = serial.Serial(port, baudrate, timeout=5, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS)
        time.sleep(2)
    except serial.SerialException as e:
        print(f"Cant open this port {port}: {e}")
        return []

    # Trying to initialize process and make controller alive
    ser.write('status\n'.encode())
    time.sleep(0.05)

    # Asking controller about vtx data
    ser.write('vtxtable\n'.encode())
    time.sleep(0.05)

    response = ""
    start_time = time.time()
    while time.time() - start_time < 5:
        if ser.in_waiting > 0:
            response += ser.read(ser.in_waiting).decode()
        time.sleep(0.05)

    ser.close()
    return response

vtxtable_data = read_vtxtable()

print(vtxtable_data)

问题根源 #

BetaFlight设备在USB刚连接后，串口处于等待唤醒的状态，需要特定的触发信号（如连续发送#字符）才能进入可响应命令的模式。初始代码仅发送普通命令，无法触发唤醒，因此设备无响应；而BetaFlight CLI会自动执行唤醒流程，所以后续代码能正常运行。

修复方案 #

模拟BetaFlight CLI的唤醒逻辑：循环发送#字符，同时检测设备是否进入CLI模式，或通过status命令验证设备已响应。

完整修复代码 #

port = '/dev/cu.usbmodem0x80000001'
baudrate = 115200

import serial
import time

def wakeup_controller(ser, timeout=10):
    cli_prompt = "Entering CLI Mode, type 'exit' to return, or 'help'"
    timeout_time = time.time() + timeout
    override_wakeup_detection = False
    buffer = ""

    def write(cmd):
        ser.write((cmd + '\n').encode())

    def get_info():
        output = ""
        start_time = time.time()
        while time.time() - start_time < 1:
            if ser.in_waiting > 0:
                output += ser.read(ser.in_waiting).decode()
            time.sleep(0.05)
        return output

    while time.time() < timeout_time and not override_wakeup_detection:
        write('#')
        time.sleep(0.1)
        
        if ser.in_waiting > 0:
            buffer += ser.read(ser.in_waiting).decode()
            if cli_prompt in buffer:
                print("# Found wakeup phrase:", cli_prompt)
                return True
            else:
                print("# No response..")
                write('status')
                time.sleep(0.1)
                output = get_info()
                if len(output) > 0:
                    print("# The board is alive")
                    override_wakeup_detection = True
                    return True
    return False

def read_vtxtable():
    try:
        ser = serial.Serial(port, baudrate, timeout=5, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS)
        time.sleep(2)
    except serial.SerialException as e:
        print(f"Cant open this port {port}: {e}")
        return []

    # 先执行唤醒流程
    if not wakeup_controller(ser):
        print("# Failed to wake up controller")
        ser.close()
        return []

    # 发送vtxtable命令
    ser.write('vtxtable\n'.encode())
    time.sleep(0.05)

    response = ""
    start_time = time.time()
    while time.time() - start_time < 5:
        if ser.in_waiting > 0:
            response += ser.read(ser.in_waiting).decode()
        time.sleep(0.05)

    ser.close()
    # 整理响应为列表格式
    return [line.strip() for line in response.split('\n') if line.strip()]

vtxtable_data = read_vtxtable()

print("VTX Table Data:")
print('[')
for line in vtxtable_data:
    print(f" '{line}',")
print(']')

运行验证 #

运行修复后的代码，输出示例：

% python3 get_data.py
# No response..
# No response..
# No response..
# The board is alive
VTX Table Data:
[
 'vtxtable',
 'vtxtable bands 8',
 'vtxtable channels 8',
 'vtxtable ...
]

内容的提问来源于stack exchange，提问作者theUkrainian