I have a question on using the I2Cmodule. I am writing the driver for an I2C EEPROM and I need to do the following for performing a read operation on the EEPROM. Note that after sending the address of the byte I want to read, I have to send a start again (without a preceeding stop). This doesn’t seem to be possible in I2C module.
How I am trying to achieve this is by doing two transactions on the I2C bus. First to write the “Byte addr” bytes. This I am ending without a STOP bit. The next to read the data byte.
==============
bool eeprom_read_byte(uint16_t address, uint8_t * data){
//Get the I2C instance handle
I2C_Type * i2c_handle = NULL;
i2c_handle = i2c_shared_init();
i2c_master_transfer_t masterXfer = {
.slaveAddress = EEPROM_I2C_SLAVE_ADDR_7BIT,
.direction = kI2C_Write,
.subaddress = (uint32_t) address,
.subaddressSize = 2,
.data = NULL,
.dataSize = 0,
.flags = kI2C_TransferNoStopFlag
};
status_t status = I2C_MasterTransferBlocking( i2c_handle, &masterXfer );
if( kStatus_Success != status ){
PRINTF(("%s[%d], %s() - I2C_MasterTransferBlocking failed: %d\r\n", __FILE__, __LINE__, __func__, status));
return FAILED;
}
masterXfer.slaveAddress = EEPROM_I2C_SLAVE_ADDR_7BIT;
masterXfer.direction = kI2C_Read;
masterXfer.subaddress = (uint32_t) address;
masterXfer.subaddressSize = 0;
masterXfer.data = data;
masterXfer.dataSize = 1;
masterXfer.flags = kI2C_TransferDefaultFlag;
status = I2C_MasterTransferBlocking( i2c_handle, &masterXfer ); è This always returns error kStatus_I2C_Busy
if (kStatus_Success != status){
PRINTF(("%s[%d], %s() - I2C_MasterTransferBlocking failed: %d\r\n", __FILE__, __LINE__, __func__, status));
return FAILED;
}
return SUCCESSFUL;
}
==============
The “kStatus_I2C_Busy” is returned from the following code inside I2C_MasterStart() function and below is the explanation of this from the reference manual.
/* Return an error if the bus is already in use. */
if (statusFlags & kI2C_BusBusyFlag)
{
result = kStatus_I2C_Busy;
}
Please suggest me how I can achieve the I2C communication needed to perform a read operation on this I2C EEPROM.
Hello Bob,
Now my understanding is that a repeated start means when a "start" is sent without a "stop" preceding it. I now think I was doing it wrong earlier. So I changed the red colored code below to "masterXfer.flags = kI2C_TransferRepeatedStartFlag". With this, I see that the read is sent on the bus. Now the problem is that no data is returned.
==========
masterXfer.slaveAddress = EEPROM_I2C_SLAVE_ADDR_7BIT;
masterXfer.direction = kI2C_Read;
masterXfer.subaddress = (uint32_t) address;
masterXfer.subaddressSize = 0;
masterXfer.data = data;
masterXfer.dataSize = 1;
masterXfer.flags = kI2C_TransferDefaultFlag;
status = I2C_MasterTransferBlocking( i2c_handle, &masterXfer ); // This always returns error kStatus_I2C_Busy
==========
With this change following is what I see on the scope:
Could you please elaborate on the workaround or could you point me to the right discussion on the forum which talks about this case?
Thanks,
Gaurav.
Hello Mark,
I figure out from the Appendix you shared that the typical issue is that the i2c master, after sending the repeated start sends a wrong slave address. But this doesn't seem to be happening in my case. Here it seems to be that I am able to read but the slave is not returning the right information.
In this, I write 0xAA at address 0x0004 and then try to read address 0x0004. What do you think could be wrong here? Do you think its the double buffering bug? how?
Cheers,
Gaurav.
This is because the write to this chip is a bit different. It does not need a repeated start.
The EEPROM datasheet I am referring to is this one:
