PIC microcontroller I2C reads fail with MPLABX generated code - pic

Question

I am using MPLABX 3.10 and I have generated a I2C Master interface using the MSSPI2C master interrupt feature. I was able to generate a I2C write event that on an osciloscope looks okay to me. Reads however are failing. When I look at the scope output I can clearly see that start condition is generated, and device ID with the read bit set is generated and acked. Next I am expecting to see the register address go out, but instead I see all zeros. Am I using the generated code incorrectly? Do I need to do a device write followed by a device read? I tried reducing the code to following:
void I2C_Initialize(void) {
i2c_object.pTrHead = i2c_tr_queue;
i2c_object.pTrTail = i2c_tr_queue;
i2c_object.trStatus.s.empty = true;
i2c_object.trStatus.s.full = false;
i2c_object.i2cErrors = 0;
// BF RCinprocess_TXcomplete; UA dontupdate; SMP Sample At Middle; P stopbit_notdetected; S startbit_notdetected; R_nW write_noTX; CKE Idle to Active; D_nA lastbyte_address;
SSP1STAT = 0x00;
// SSPEN enabled; WCOL no_collision; SSPOV no_overflow; CKP Idle:Low, Active:High; SSPM FOSC/4_SSPxADD;
SSP1CON1 = 0x28;
// BOEN disabled; AHEN disabled; SBCDE disabled; SDAHT 100ns; DHEN disabled; ACKTIM ackseq; PCIE disabled; SCIE disabled;
SSP1CON3 = 0x00;
// Baud Rate Generator Value: SSPADD 3;
SSP1ADD = 0x03;
/* Byte sent or received */
// clear the master interrupt flag
PIR1bits.SSP1IF = 0;
// enable the master interrupt
PIE1bits.SSP1IE = 1;
}
void I2C_MasterRead(
uint8_t *pdata,
uint8_t length,
uint16_t address,
I2C_MESSAGE_STATUS *pflag) {
static I2C_TRANSACTION_REQUEST_BLOCK trBlock;
// check if there is space in the queue
if (i2c_object.trStatus.s.full != true) {
I2C_MasterReadTRBBuild(&trBlock, pdata, length, address);
I2C_MasterTRBInsert(1, &trBlock, pflag);
} else {
*pflag = I2C_MESSAGE_FAIL;
}
}
void I2C_MasterReadTRBBuild(
I2C_TRANSACTION_REQUEST_BLOCK *ptrb,
uint8_t *pdata,
uint8_t length,
uint16_t address) {
ptrb->address = address << 1;
// make this a read
ptrb->address |= 0x01;
ptrb->length = length;
ptrb->pbuffer = pdata;
}
void main(void) {
#define BMA222E_BASE_ADDRESS_DEV0 (0x18) // <BMA222E base address
uint8_t dummy[2];
I2C_MESSAGE_STATUS pflag;
/* Configure the oscillator for the device */
ConfigureOscillator();
I2C_Initialize();
dummy[0] = 0x0F; // I expect to see 0x0F go out as the register value
dummy[1] = 0x00;
I2C_MasterRead (&dummy, 2, BMA222E_BASE_ADDRESS_DEV0, &pflag);
}

Answer 1

Ok, so figured it out. I need to write the address and then read the data in two steps. I modified the main function as follows.
void main(void) {
#define BMA222E_BASE_ADDRESS_DEV0 (0x18) // <BMA222E base address
uint8_t dummy[2];
I2C_MESSAGE_STATUS pflag;
/* Configure the oscillator for the device */
ConfigureOscillator();
I2C_Initialize();
dummy[0] = 0x0F; // I expect to see 0x0F go out as the register value
dummy[1] = 0x00;
I2C_MasterWrite (&dummy, 1, BMA222E_BASE_ADDRESS_DEV0, &pflag);
I2C_MasterRead (&dummy, 1, BMA222E_BASE_ADDRESS_DEV0, &pflag);
// dummy[0] now contains the read data.
}