Part Number: MSP-EXP430F5529LP
Other Parts Discussed in Thread: MSP430F5529
I've got my I2C library working fine, but for some reason I have to read an additional dummy byte after sending the STOP condition, or else it won't read the actual final byte and everything gets truncated. I still can't figure out why this is happening. Here's the read section of my code:
case READ:
UCB0CTL1 &= ~UCTR; // set listener mode
UCB0CTL1 |= UCTXSTT; // send a START
while(UCB0CTL1 & UCTXSTT) ; // wait for start condition done
if (!(UCB0CTL1 & UCTXSTT) && (UCB0IFG & UCNACKIFG)) { // peripheral n'acked on address
UCB0CTL1 |= UCTXSTP;
while(UCB0CTL1 & UCTXSTP) ;
return NACK_ADDR;
}
while (!(UCB0IFG & UCRXIFG)) ;
if (length == 1) {
UCB0CTL1 |= UCTXSTP; // we must set the STOP bit while the first byte is being read,
// if it's a single byte only read
UCB0IFG &= ~UCTXIFG;
*data = UCB0RXBUF;
while(UCB0CTL1 & UCTXSTP) ; // wait for STOP to complete
return SUCCESS;
} else {
for(i = 0; i < length; i++) {
if(i == length - 1) { // if we are on the last byte, it's a special case
UCB0CTL1 |= UCTXSTP; // send stop
*(data + i) = UCB0RXBUF; // read byte
UCB0IFG &= ~UCTXIFG;
while(UCB0CTL1 & UCTXSTP) ; // wait for STOP to complete
break;
}
*(data + i) = UCB0RXBUF; // read byte
while (!(UCB0IFG & UCRXIFG)) ; // wait for next byte to come
}
dummyByte = UCB0RXBUF; // read a dummy byte or everything gets messed up
}
When I read say, 3 bytes, I can see that the dummyByte read does indeed read a 4th byte on the bus, typically 0xFF because that's what the chip sends. If I comment out this line, the chip will only read TWO bytes. I already have to do the weird last byte special case because the MSP430F5529 requires us to send the STOP condition before reading the final byte.
This doesn't really matter, as everything works -- it's just one of those irritating little bugs that I want to fix but haven't been able to. Any suggestions are greatly welcomed!
In this example, if I were to eliminate the dummyByte line, *data would contain 0x72, 0x76 and then the next time around, it would contain 0xBC, 0x72, etc. It's like the buffer isn't being cleared, hence why I added the dummyByte read in the first place.
