在Raspberry Pi 2上接收错误的串行数据

Question

我已将超声波距离传感器连接到树莓派2.当触发时，传感器应通过串口发回以下6个参数：

  

  
1. 帧头：0xFF
  
2. 数据1：0x07
  
3. 数据2：0xD0
  
4. 数据3：0x01
  
5. 数据4：0x19
  
6. 校验和：0xF0
  

然而，当我尝试阅读输出时，我会得到类似这样的内容：['\x00\xff\x01V\x00\xce']

以下是有关传感器串行帧格式的一些信息：

校验和的计算如下：

SUM =( Frame header + Data_H+ Data_L+ Temp_H+ Temp_L)&0x00FF 注意：校验和仅保留8位的低累加值;

这是我到目前为止编写的代码：

import RPi.GPIO as GPIO
import time
from serial import Serial

GPIO.setmode(GPIO.BCM) #GPIO mode
GPIO_TRIGGER = 18      #assign GPIO pins
GPIO.setup(GPIO_TRIGGER, GPIO.OUT) #direction of GPIO-Pins (IN / OUT)

data_output=[]

def uss_funct():
    ser = Serial('/dev/ttyAMA0', baudrate=9600, bytesize=8, parity='N', stopbits=1)

    # set trigger HIGH, sensor is waiting for falling edge
    time.sleep(0.01000)
    GPIO.output(GPIO_TRIGGER, True)

    # set trigger LOW after 10ms -> Falling Edge
    time.sleep(0.01000)
    GPIO.output(GPIO_TRIGGER, False)

    # set trigger back HIGH after 2ms, as LOW is supposed to be between 0.1-10ms
    time.sleep(0.00200)
    GPIO.output(GPIO_TRIGGER, True)

    #read from rx
    data_output.append(ser.read(6))
    ser.close()

    #clean up GPIO pins
    GPIO.cleanup()

    print (data_output)

if __name__ == '__main__':
    uss_funct()

Answer 1

校验和可以很容易地计算，但问题是数据不同步。第一个字节需要是0xff。这里有一些代码可以找到数据的前面（0xff），然后计算温度，距离和校验和：

data_output = ser.read(6)

# the first byte should be 0xff
if len(data_output) == 6 and \
        data_output[0] != 0xff and 0xff in data_output:

    # find where 0xff is in the data stream
    still_needed = data_output.index(0xff)

    # read more data, we are out of sync
    data_output = data_output[still_needed:] + ser.read(still_needed)

# must get 6 bytes, and the first needs to be 0xff
if len(data_output) != 6 or data_output[0] != 0xff:
    good_data = False
else:
    # verify the checksum
    good_data = (0 == (sum(data_output) & 0xff))

if good_data:
    distance = data_output[1] * 256 + data_output[2] 
    temperature = data_output[3] * 256 + data_output[4]

确保使用超时初始化串行对象：

from serial import Serial
ser = Serial(..., timeout=1)

我没办法测试这个，所以买家要小心。