Using I2C_master library AVR

Question

I am using I2C_master library for AVR, Communication works fine, but I have little problem, how can I get data.

I am using this function

uint16_t i2c_2byte_readReg(uint8_t devaddr, uint16_t regaddr, uint8_t* data, uint16_t length){

devaddr += 1;
if (i2c_start(devaddr<<1|0)) return 1;

i2c_write(regaddr >> 8);
i2c_write(regaddr & 0xFF);

if (i2c_start(devaddr<<1| 1)) return 1;

for (uint16_t i = 0; i < (length-1); i++)
{
    data[i] = i2c_read_ack();
}
data[(length-1)] = i2c_read_nack();

i2c_stop();

return 0;}

And now I need to use received data, and send it by UART to PC

    uint8_t* DevId;

    i2c_2byte_readReg(address,REVISION_CODE_DEVID,DevId,2);
    deviceH=*DevId++;
    deviceL=*DevId; 
    UART_send(deviceH); 
    UART_send(deviceL); 

I think that I am lost with pointers. Could you help me, how can I get received data for future use? (UART works fine for me in this case, but it sends only 0x00 with this code)

Answer 1

The function i2c_2byte_readReg takes as a third argument a pointer to the buffer where the data will be written. Note that it must have size bigger than the forth argument called length. Your DevId pointer doesn't point to any buffer so when calling the function you've got an access violation.

To get the data you should define an array before calling the function:

const size_t size = 8;
uint8_t data[size];

Then you can call the function passing the address of the buffer as an argument (the name of the array is converted into its address):

const uin16_t length = 2;    
i2c_2byte_readReg(address, REVISION_CODE_DEVID, data, length);

Assuming that the function works well those two bytes will be saved into data buffer. Remember that size must be bigger or equal to length argument.

Then you can send the data over UART:

UART_send(data[0]); 
UART_send(data[1]);