使用pymodbus作为串行/RTU主机运行ArduinoModbus的Modbus丢失字节错误

Question

我面临一些与Modbus RTU实现有关的问题。我有2x Arduino MKR和RS485 hats/扩展作为我的2个从设备(使用ArduinoModbus库)。我正在尝试使用python和pymodbus库轮询我的个人电脑(Windows)上的设备，运行速度为9600波特。

我可以成功地传输数据。最初的理智测试是一个简单的analogRead()在一个Arduino(传感器1)上，写入它的内部保持寄存器，然后进行pymodbus主投票/注册请求。

我现在连接了第二个Arduino (传感器2)，它有一个I2C连接到一个流传感器。arduino正在运行，通过I2C读取传感器，并用数据更新5倍的保存寄存器。主机(PC)一个接一个地轮询Arduino(传感器1和传感器2)。它总是成功地获取传感器1的数据(只有一个寄存器)，但间歇性地失败了获取传感器2的数据(5个寄存器)。python控制台如下所示：

Sensor 2: 0,25000,0,0, 0
Sensor 2: 0,25000,0,0, 0
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response
Sensor 2: 0,25000,0,0, 0
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response
Sensor 2: 0,25000,0,0, 0
Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response

对日志进行更深入的研究就会发现，这个问题并不是所有Bytes人都在解决的问题，如下所示：

11/24/2022 03:52:59 PM Running transaction 4
11/24/2022 03:52:59 PM SEND: 0x1 0x3 0x0 0x0 0x0 0x5 0x85 0xc9
11/24/2022 03:52:59 PM Changing state to IDLE - Last Frame End - 1669265577.447308, Current Time stamp - 1669265579.457942
11/24/2022 03:52:59 PM New Transaction state "SENDING"
11/24/2022 03:52:59 PM Changing transaction state from "SENDING" to "WAITING FOR REPLY"
11/24/2022 03:52:59 PM {msg_start} received, Expected 15 bytes Received 11 bytes !!!!
11/24/2022 03:52:59 PM Changing transaction state from "WAITING FOR REPLY" to "PROCESSING REPLY"
11/24/2022 03:52:59 PM RECV: 0x1 0x3 0xa 0x0 0x0 0x61 0xa8 0x0 0x0 0x0 0x0
11/24/2022 03:52:59 PM Frame - [b'\x01\x03\n\x00\x00a\xa8\x00\x00\x00\x00'] not ready
11/24/2022 03:52:59 PM Getting transaction 1
11/24/2022 03:52:59 PM Changing transaction state from "PROCESSING REPLY" to "TRANSACTION_COMPLETE"
11/24/2022 03:52:59 PM Modbus Error: [Input/Output] No Response received from the remote unit/Unable to decode response
11/24/2022 03:53:01 PM Current transaction state - TRANSACTION_COMPLETE

现在，我已经完全删除了向传感器1请求数据，并且我的python脚本只能从传感器2(问题传感器)请求，但问题仍然存在，我的python脚本如下所示：

import serial
import time
import logging
from pymodbus.client import ModbusSerialClient
from pymodbus.transaction import ModbusRtuFramer

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
handler = logging.FileHandler('main.log', 'w', 'utf-8')
handler.setFormatter(logging.Formatter(fmt='%(asctime)s %(message)s', datefmt='%m/%d/%Y %I:%M:%S %p'))
logger.addHandler(handler)

client = ModbusSerialClient("COM12", ModbusRtuFramer, baudrate=9600, timeout=10, reset_socket=False)
client.connect()

while(1):

    c2 = client.read_holding_registers(0,5,1)
    if c2.isError():
        logger.error(msg=c2)
        print(c2)
    else:    
        print(f"Sensor 2: {c2.getRegister(0)},{c2.getRegister(1)},{c2.getRegister(2)},{c2.getRegister(3)}, {c2.getRegister(4)}")
    
    time.sleep(2)

我不太确定什么是失火..。我可以很好地使用像QModMaster这样的图形用户界面来处理传感器2的数据，我知道它在引擎盖下使用libmodbus。我应该使用python库pylibmodbus吗？它需要本地编译的libmodbus，这对Windows来说有点麻烦.

我是不是漏掉了一个能帮上忙的pymodbus设置？

我已经尝试过更改pymodbus超时，但没有起作用。我尝试降低流量传感器的采样率，以降低频率，并确保Arduino是免费的/可用于Modbus请求。这是行不通的，事实上，减少它使问题变得更糟。

我尝试向python代码(time.sleep(2))添加基本延迟，以减缓Modbus请求的速度，但这对错误没有影响。

希望有人知道发生了什么，因为我已经花了很长时间在网上搜索资源，以找到答案，但没有用。如果我最后需要更多的澄清，我可以提供:)

谢谢!

P.S. Arduino代码，供参考

#include <Arduino.h>
#include <ArduinoRS485.h>
#include <ArduinoModbus.h>
#include <Wire.h>

/**
 * Modbus slave/server
*/

#define SAMPLE_RATE 50

const int ADDRESS = 0x08; // Sensor I2C Address
const float SCALE_FACTOR_FLOW = 500.0; // Scale Factor for flow rate measurement
const float SCALE_FACTOR_TEMP = 200.0; // Scale Factor for temperature measurement

int count = 0;
unsigned long startMillis;
unsigned long currentMillis;

enum error_types{
  no_error,
  write_mode_error, 
  read_error
  };

enum error_types error; 

// Protoypes
int stop_continuous_measurement();
int start_continous_measurement();

void setup() {
  int ret;

  // Start Serial and I2C
  Serial.begin(9600); // initialize serial communication
  Wire.begin();       // join i2c bus (address optional for master)

  // Set up MODBUS
  if (!ModbusRTUServer.begin(0x01,9600)) {
    Serial.println("Could not begin ModbusRTU server...");
    while(1);
  }

  // configure holding registers at address 0x00, 4 registers for data
  ModbusRTUServer.configureHoldingRegisters(0x00, 5);

  // start sensor
  do {
    // Soft reset the sensor
    Wire.beginTransmission(0x00);
    Wire.write(0x06);
    ret = Wire.endTransmission();
    if (ret != 0) {
      Serial.println("Error while sending soft reset command, retrying...");
      delay(500); // wait long enough for chip reset to complete
    }
  } while (ret != 0);

  delay(50); // wait long enough for chip reset to complete

  // To perform a measurement, first send 0x3608 to switch to continuous
  if(start_continous_measurement() !=0) {
    error = write_mode_error;
  }

  startMillis = millis();
}

void loop() {

  ModbusRTUServer.poll();

  uint16_t aux_value;
  uint16_t sensor_flow_value;
  uint16_t sensor_temp_value;
  int16_t signed_flow_value;
  int16_t signed_temp_value;
  float scaled_flow_value;
  float scaled_temp_value;
  byte aux_crc;
  byte sensor_flow_crc;
  byte sensor_temp_crc;

  // measurement mode (H20 calibration), then read 3x (2 bytes + 1 CRC byte) from the sensor.
  // To perform a IPA based measurement, send 0x3615 instead.
  // Check datasheet for available measurement commands.

  error = no_error;

  currentMillis = millis();

  if(currentMillis - startMillis > SAMPLE_RATE){
    Wire.requestFrom(ADDRESS, 9);
    if (Wire.available() < 9) {
      error = read_error;
    }
    else{
      sensor_flow_value  = Wire.read() << 8; // read the MSB from the sensor
      sensor_flow_value |= Wire.read();      // read the LSB from the sensor
      sensor_flow_crc    = Wire.read();
      sensor_temp_value  = Wire.read() << 8; // read the MSB from the sensor
      sensor_temp_value |= Wire.read();      // read the LSB from the sensor
      sensor_temp_crc    = Wire.read();
      aux_value          = Wire.read() << 8; // read the MSB from the sensor
      aux_value         |= Wire.read();      // read the LSB from the sensor
      aux_crc            = Wire.read();

      signed_flow_value = (int16_t) sensor_flow_value;
      scaled_flow_value = ((float) signed_flow_value) / SCALE_FACTOR_FLOW;

      signed_temp_value = (int16_t) sensor_temp_value;
      scaled_temp_value = ((float) signed_temp_value) / SCALE_FACTOR_TEMP;
    
      // write to MODBUS registers
      ModbusRTUServer.holdingRegisterWrite(0, (uint16_t) count);
      ModbusRTUServer.holdingRegisterWrite(1, (uint16_t) scaled_temp_value*1000);
      ModbusRTUServer.holdingRegisterWrite(2, (uint16_t) scaled_flow_value*1000);
      ModbusRTUServer.holdingRegisterWrite(3,(uint16_t) aux_value);
      ModbusRTUServer.holdingRegisterWrite(4, (uint16_t) error);
    }
    startMillis = currentMillis;
  }
}

int start_continous_measurement() {
  Wire.beginTransmission(ADDRESS);
  Wire.write(0x36);
  Wire.write(0x08);
  return Wire.endTransmission();
}

int stop_continuous_measurement() {
    // To stop the continuous measurement, first send 0x3FF9.
    Wire.beginTransmission(ADDRESS);
    Wire.write(0x3F);
    Wire.write(0xF9);
    return Wire.endTransmission();
}

Answer 1

日志显示，只接收到部分数据：Expected 15 bytes Received 11 bytes。这可能是由错误的字符间计时引起的，即字符之间的静默时间被错误地解释为消息的结束。通过指定client.strict = False，实现了Modbus规范的字符间定时.

还可以看到类似的故事：Pymodbus :响应中的错误字节计数和pymodbus 问题。