Communicating with a raspberry pi via i2c

Hi everyone,

I am trying to set up a MSP430G2553 as a slave to relay ADC information to a raspberry pi. Here's the relevant part of my code:

#include <msp430.h>

volatile int i = 0;

volatile int bytectr = 0;

volatile int output[3] = {0};

volatile int RXData = 0;

volatile int reg = 0;

volatile int VAR_INPUT[34];

void getadc();

void inttoarray();

int main(void)

{

WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

//BCSCTL1 = CALBC1_1MHZ;                  // Set range

//DCOCTL = CALDCO_1MHZ;        // SMCLK = DCO = 1MHz

P1SEL |= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0

P1SEL2|= BIT6 + BIT7;                     // Assign I2C pins to USCI_B0

//P1DIR |= BIT0;

//P1OUT &= ~BIT0;

UCB0CTL1 |= UCSWRST;                      // Enable SW reset

UCB0CTL0 = UCMODE_3 + UCSYNC; // I2C Slave, synchronous mode

UCB0I2COA = 0x48;                         // Own Address is 048h

UCB0CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation

UCB0I2CIE |= UCSTPIE + UCSTTIE;           // Enable STT and STP interrupt

IE2 |= UCB0TXIE;                          // Enable RX interrupt

//__enable_interrupt();

while (1)

{

  __bis_SR_register(CPUOFF + GIE);        // Enter LPM0 w/ interrupts

}

}

void inttoarray()

{

VAR_INPUT[0] = reg;

if(reg == 0)

VAR_INPUT[0] = 8;

VAR_INPUT[1] = RXData / 256;

RXData -= VAR_INPUT[1] * 256;

VAR_INPUT[2] = RXData;

}

#pragma vector = USCIAB0TX_VECTOR

__interrupt void USCIAB0TX_ISR(void)

{

//VAR_INPUT[0] = 0x11;

//VAR_INPUT[1] = 0x22;

//VAR_INPUT[2] = 0x33;

//VAR_INPUT[3] = 0x44;

while((IFG2 & UCB0TXIFG) == 0);

UCB0TXBUF = VAR_INPUT[i];

i++;

}

#pragma vector = USCIAB0RX_VECTOR// Received start bit

__interrupt void USCIAB0RX_ISR(void)

{

//UCB0TXBUF = 0x44;

//__delay_cycles(1000);

if(UCB0CTL1 & UCTR) //data requested

{

// if(UCB0STAT & UCSTTIFG)

// {

//getadc();  //<- ideally I would like this here

// }

i = 0;

bytectr = 0;

UCB0STAT &= ~(UCSTPIFG + UCSTTIFG);       // Clear interrupt flags

if (bytectr != 0)                            // Check TX byte counter

__bic_SR_register_on_exit(CPUOFF);      // Exit LPM0 if data was　

}

else

{

  reg = UCB0RXBUF;

UCB0STAT &= ~UCSTPIFG; // Clear start condition int flag

  if(reg == 8)

  reg = 0; //use 0 internally

  bytectr = 3;

  getadc();

  __bic_SR_register_on_exit(CPUOFF);        // Exit LPM0

  //  TXData++;                                 // Increment data

}

}

void getadc()

{

ADC10CTL0 &= ~ENC; // Disable ADC

ADC10CTL1 = (reg *0x1000u) + ADC10DIV_3;        // Temp Sensor ADC10CLK/4

ADC10CTL0 = ADC10ON | ADC10SHT_0 | SREF_0;                                                        // reference generator ON/ADC10 ON

ADC10CTL0 |= ENC + ADC10SC;                     // Sampling and conversion start

while ( ADC10CTL1 & ADC10BUSY );                // Wait for ADC to complete

RXData = ADC10MEM;

inttoarray();

}

Here is what the master sends:

START (transmit)

REGISTER_BYTE

STOP

START (receive)

(I would ideally like to call getadc() here)

RECIEVED_BYTE_1

RECIEVED_BYTE_2

RECIEVED_BYTE_3

STOP

The code works fine with a MSP430 as the master(unless my master has issues as well) but not with the Pi. The Pi appears to send the register byte correctly but it seems to cut off the first bit of the first byte of RECIEVED_BYTE_1 with the rest of the transmission being lost. I noticed that when I comment out getadc(), the pi will receive any bytes I send it. I'm new to i2c and find this very confusing. Any help would be really appreciated.