如何通过 I2C 将浮点数从 Raspberry Pi 发送到 STM32F205？

Question

我想将 Raspberry Pi3 用作主设备，并通过 I2C 将 ID、电压、电流、电压相位、电流相位、频率作为浮点数发送到我的 STM32。 我不知道如何在 python 在 Raspberry Pi 上做到这一点。 直到现在我用 Arduino Nano 做到了这一点，我工作得很好。 代码如下所示：

// ATTENTION
// to get scanf and printf to work with floats on Arduino, edit the file "platform.txt" in directory
// C:\Program Files (x86)\Arduino\hardware\arduino\avr\
// goto lines with "compiler.c.extra_flags=" and "compiler.c.elf.extra_flags=" and add the following
// =-Wl,-u,vfprintf -lprintf_flt -lm -Wl,-u,vfscanf -lscanf_flt -lm
// then the printing will work fine


`#include <Wire.h>

template<typename T>
struct I2C_Data
{
  T u, i, u_phase, i_phase, f;
};

template<typename T>
void i2c_tx(uint8_t addr, T &data)
{
  uint8_t *src = (uint8_t *) &data;
  Wire.beginTransmission(addr);
  for (unsigned int i = 0; i < sizeof(T); i++)
  {
    Wire.write(src[i]);
  }
  Wire.endTransmission();
}

void setup()
{
  Wire.begin();         // join i2c bus (address optional for master)
  Serial.begin(115200);
}

void loop()
{
  static int oldCnt = 0;
  static char strBuf[256];
  static I2C_Data<float> i2c_data = { 0, 0, 0, 0, 0 };

  const int cnt = Serial.available();
  if (cnt > 0 && cnt == oldCnt)
  {
    for (int i = 0; i < cnt; i++)
    {
      strBuf[i] = Serial.read();
    }
    strBuf[cnt] = 0;

    int idx = 0;
    sscanf(strBuf, "%d %f %f %f %f %f", &idx, &i2c_data.u, &i2c_data.i, &i2c_data.u_phase, &i2c_data.i_phase, &i2c_data.f);
    sprintf(strBuf, "[%d] =  %3.0f V  |  %.3f A  |  %4.0f °  |  %4.0f °  |  %.0f Hz\n", idx, i2c_data.u, i2c_data.i, i2c_data.u_phase, i2c_data.i_phase, i2c_data.f);
    idx |= 8;
    Serial.print(strBuf);

    i2c_tx(idx, i2c_data);

    oldCnt = 0;
  }
  else
  {
    oldCnt = cnt;
    delay(1);
  }
}```


How should my python Code look like, that it will work as the Arduino Code?

I tried so send something from the RasPi with I2C and the value is written into the DataRegister (DR) of the I2C SFR from the STM32. I dont know how to convert the value into float and store it into a variable.

Answer 1

也许不是 OP 的关键问题，但有一些问题值得改进：

测试sscanf()结果

扫描完成了吗？

// sscanf(strBuf, "%d %f %f %f %f %f", ...);
if (sscanf(strBuf, "%d %f %f %f %f %f", ...) != 6) {
  Handle_Error();  // TBD code for OP.
}

避免缓冲区溢出。 检测缓冲区是否太小。

1. 使用%g减少大值的文本 output。
2. 使用snprintf()限制 output。

    //sprintf(strBuf, "[%d] =  %3.0f V  |  %.3f A  |  %4.0f °  |  %4.0f °  |  %.0f Hz\n", 
    //    idx, i2c_data.u, i2c_data.i, i2c_data.u_phase, i2c_data.i_phase, i2c_data.f);
    int n = snprintf(strBuf, sizeof strBuf, 
        "[%d] =  %3.0g V  |  %.3g A  |  %4.0g °  |  %4.0g °  |  %.0g Hz\n", 
        idx, i2c_data.u, i2c_data.i, i2c_data.u_phase, i2c_data.i_phase, 
    if (n < 0 || (unsigned) n >= sizeof strBuf) {
      Handle_error();
    } 

测试cnt

   if (cnt >= 256) HandleError();