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 (®, 1);
reason(why);
why = bcm2835_i2c_read_register_rs(®,&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
答案 0 :(得分：0)
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......
答案 1 :(得分：0)
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