通过SMBus / I2C使用bcm2835更改mlx90614的从站地址

Question

如何使用bcm2835库更改mlx90614的从站地址？我试过跟随代码...

int main()
{
   // Buffer, where I store data which I'll send
   unsigned char buf[6];

   // bcm2835 i2c module intialisation code
   bcm2835_init();
   bcm2835_i2c_begin();
   bcm2835_i2c_set_baudrate(25000);
   bcm2835_i2c_setSlaveAddress(0x00);

   // For debug purposes, I read what reason codes operations give.
   bcm2835I2CReasonCodes why;
   bcm2835_i2c_begin();

   // function which reads and prints what value eeprom address 0x0e has. 
   // See below the main.

   printf("Initial check\n");
   check(); // this time it prints a factory default value 0x5a.

   // To access eeprom, the command must start with 0x2X, where x determines the          
   // address, resulting 0x2e.
   buf[0] = 0x2e;

   // According to datasheet, I first have to clear the address before 
   // real write operation.
   buf[1] = 0x00;
   buf[2] = 0x00;
   why = bcm2835_i2c_write(buf,3);
   reason(why); // resolves and prints the reason code. This time it prints OK

   // according to datasheet, eeprom needs 5ms to make a write operation,
   // but I give it 2 seconds.       
   sleep(2); 

   // Then I check did the value in eeprom 0x0e change. IT DOESN'T!
   printf("Check after clear\n");       
   check();

   // Then I try to write a new address to the eeprom but since the clearing 
   // the register didn't work, this is very unlikely to work either.
   buf[0] = 0x2e;
   buf[1] = 0x4b;
   buf[2] = 0x00;
   why = bcm2835_i2c_write(buf,3);
   reason(why);
   sleep(2); 

   // The datasheet says that I have to reset the power supply and after that
   // the device should respond to the new slave address.
   // I do that by pluging off the jumper wires and reconnecting them 
   // after the program has finnished.
   bcm2835_i2c_end();
   return 0;
}

// The function I use to determine what the reason code was.
void reason(bcm2835I2CReasonCodes why)
{
   printf("Reason is: ");
   if(why == BCM2835_I2C_REASON_OK)
   {
      printf("OK");
   }else if(why == BCM2835_I2C_REASON_ERROR_NACK){
      printf("NACK");
   }else if(why == BCM2835_I2C_REASON_ERROR_CLKT){
      printf("Clock stretch");
   }else if(why == BCM2835_I2C_REASON_ERROR_DATA ){
      printf("Data error");
   }else{
      printf("Dunno lol");
   }
   printf("\n");
   return;
}

// Here I read eeprom 0x2e.
void check()
{
   unsigned char buf[6];
   unsigned char reg = 0x2e;
   bcm2835I2CReasonCodes why;
   // better safe than sorry with the buffer :)
   buf[0] = 0;
   buf[1] = 0;
   buf[2] = 0;
   why = bcm2835_i2c_write (&reg, 1);
   reason(why);
   why = bcm2835_i2c_read_register_rs(&reg,&buf[0],3);
   reason(why);
   printf("Buffer values are: %x ; %x ; %x \n", buf[0], buf[1], buf[2]);
}

该计划的输出如下：

Initial check
Reason is: OK
Reason is: OK
Buffer values are: 5a ; be ; dc
Reason is: OK
Check after clear
Reason is: OK
Reason is: OK
Buffer values are: 5a ; be ; dc
Reason is: OK

如果我之后运行i2cdetect -y 1，设备不会出现在表中，但它会响应从0x00或0x5a调用它的程序。在我使用这样的程序之后，i2cdetect通常从地址0x5a检测到设备。

所以我猜真正的问题是，为什么我无法清除并重写eeprom 0x0e？

可以在下面找到Mlx90614 SMBus通信的描述。最相关的页面是IMO第19页，它实际上给出了我正在尝试做的伪代码示例。 http://www.melexis.com/Assets/SMBus-communication-with-MLX90614-5207.aspx

这是mlx90614的数据表 http://www.melexis.com/Assets/IR-sensor-thermometer-MLX90614-Datasheet-5152.aspx

这是bcm2835的文档 www.airspayce.com/mikem/bcm2835/group__i2c.html

Answer 1

与我的mlx90614s完全相同的问题挣扎。这是我用来解决它的写例程（请注意，在调用例程之前，bcm2835库已正确初始化）。

首先，我使用＆＃34;正确＆＃34;来调用写例程。 Slaveaddress，命令= 0x2E（EEPROMAccess | SMBusAddressReg）和data = 0x0000（用于擦除）。 ＆＃34;正确＆＃34;从地址可以是0x00或出厂默认值0x5a（或者芯片的真实地址）。

擦除后，我使用了相同的写例程，但现在使用数据= 0x005b，从出厂默认值0x5a更改为0x5b，执行了电源关闭复位（POR），并且设备使用i2cdetect显示其新地址（0x5b）

uint8_t memWriteI2C16(uint8_t SlaveAddress, uint8_t command, uint16_t data)
{    
unsigned char arr[5];
uint8_t status;

//Prepare for CRC8 calc
arr[0] = SlaveAddress<<1;        //NB! 7 bit address + a 0 write bit.      
arr[1] = command;                //Command byte in packet       
arr[2] = *((uint8_t *)(&data));  //Extract data low byte
arr[3] = *((uint8_t *)(&data)+1);//Extract data high byte
arr[4] = crc8(&arr[0],4)&0xFF;   //Calculate PEC by CRC8

bcm2835_i2c_setSlaveAddress(SlaveAddress);//Transmit address byte to I2C/SMBus
status = bcm2835_i2c_write (&arr[1], 4);  //Transmit Command,DataL, DataH and PEC       
bcm2835_delay(5);                         //Delay at least 5ms
return (status);
}

我使用的CRC8例程是：

// Return CRC-8 of the data, using x^8 + x^2 + x + 1 polynomial.  
// A table-based algorithm would be faster, but for only a few bytes 
// it isn't worth the code size. 
// Ref: https://chromium.googlesource.com/chromiumos/platform/vboot_reference/+/master/firmware/lib/crc8.c
uint8_t crc8(const void *vptr, int len)
{
 const uint8_t *data = vptr;
 unsigned crc = 0;
 int i, j;
 for (j = len; j; j--, data++) {
    crc ^= (*data << 8);
    for(i = 8; i; i--) {
        if (crc & 0x8000)
            crc ^= (0x1070 << 3);
        crc <<= 1;
    }
 }
 return (uint8_t)(crc >> 8);
}

另外：根据mlx90614的数据表，上电后的默认出厂状态是PWM输出。将处于工厂PWM状态的mlx90614连接到RPi2上的I2C总线时，i2cdetect会报告总线上的数百个I2C设备。尝试使用bcm2835库访问mlx90614失败。所需要的是通过将SCL保持低电平至少2ms来强制mlx90614退出其PWM状态。这是我做的：

uint8_t mlx90614SMBusInit()
{
//Hold SCL low for at leat 2ms in order to force the mlx90614 into SMBus-mode
//Ref Melix app note regarding SMBus comm chapter 6.1 and table 5. 
uint8_t SCL1 = 3; //BCM2835 pin no 3 -RPi2 and RevB+. Use if i2cdetect -y 1
uint8_t SCL0 = 1; //BCM2835 pin no 1 -RPi2 and RevB+. Use if i2cdetect -y 0
uint8_t SCL;

SCL = SCL1; 
bcm2835_gpio_fsel(SCL, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(SCL ,LOW);
bcm2835_delay( 3); //Delay >2 ms
bcm2835_gpio_write(SCL ,HIGH); 
return (1);
}

但是，这只能持续到下一次加电。因此，需要在mlx90614的eeprom中写入pwmctrl寄存器（禁用pwm输出并强制SDA到OpenDrain）。我使用了如前所述的write例程with command = 0x22（即EEPROMAccess | PWMCTRLAddressRegister），在擦除pwmctrl寄存器内容后，我写了0x0200（我的设备中的第一个3个半字节是020 ......）。电源关闭复位（POR），器件以SMBus模式启动（I2C总线无干扰）。 mlx90614是一个棘手的小组件......

Answer 2

如果您正在使用任何Linux发行版中的I2C-tools软件包（在我的情况下，我使用的是debian distro），也可以使用i2cset命令（https://manpages.debian.org/buster/i2c-tools/i2cset.8.en.html）更改地址，这是一个示例：< / p>

#Find your I2C bus in your linux with the command i2cdetect -l 
#(in my case is the i2c-1)
i2cdetect -l
i2c-1   i2c             bcm2835 I2C adapter                     I2C adapter

#Write the word 0x0000 to the address 0x2E and append the PEC check byte.
i2cset -y 1 0x5a 0x2E 0x0000 wp 

#Write the new address as a word, to the address 0x2E and append the PEC 
#check byte. In my case the new address is 0x005c
i2cset -y 1 0x5a 0x2E 0x005c wp

#Perform a power cycle of the Mlx90614 device
#Check the new address with the command i2cdetect -y 1
i2cdetect -y 1