MSP430 I2C Library

#include <stdint.h>
#include <msp430.h>
#include "i2c.h"

volatile uint8_t *i2c_out_buffer;
volatile uint16_t i2c_out_buffer_size;
volatile uint8_t *i2c_in_buffer;
volatile uint16_t i2c_in_buffer_size;

void i2c_init() {
    P4SEL |= BIT1 | BIT2;
    UCB1CTL1 = UCSWRST;
    UCB1CTL0 = UCMST | UCSYNC | UCMODE_3;
    UCB1CTL1 |= UCSSEL__SMCLK;
    UCB1BR0 = 50; // 400 kHz
    UCB1BR1 = 0;
    UCB1CTL1 &= ~UCSWRST;
    UCB1IE = UCNACKIE | UCTXIE | UCRXIE;
}

int i2c_busy() {
    return (UCB1STAT & UCBBUSY);
}

void i2c_request(uint8_t addr, uint8_t *send_buffer, uint16_t send_buffer_size, uint8_t *recv_buffer, uint16_t recv_buffer_size, int wait) {
    while (i2c_busy());
    i2c_out_buffer = send_buffer;
    i2c_out_buffer_size = send_buffer_size;
    i2c_in_buffer = recv_buffer;
    i2c_in_buffer_size = recv_buffer_size;
    UCB1I2CSA = addr;
    i2c_nack = 0;
    if (send_buffer_size) {
        UCB1CTL1 |= UCTR;
    } else {
        UCB1CTL1 &= ~UCTR;
        if (i2c_in_buffer_size == 1) {
            UCB1CTL1 |= UCTXNACK;
        }
    }
    UCB1CTL1 |= UCTXSTT;
    if (wait) {
        while (i2c_out_buffer_size || i2c_in_buffer_size);
    }
}

void __attribute__((interrupt(USCI_B1_VECTOR))) USCI_B1_ISR() {
    switch (UCB1IV) {
        case 2: // Arbitration lost
            break;
        case 4: // No ACK
            UCB1CTL1 |= UCTXSTP;
            i2c_nack = 1;
            break;
        case 6: // Start received
            break;
        case 8: // Stop received
            break;
        case 12: // Data sent
            if (i2c_out_buffer_size) {
                UCB1TXBUF = *i2c_out_buffer;
                i2c_out_buffer++;
                i2c_out_buffer_size--;
            } else {
                if (i2c_in_buffer_size) {
                    UCB1CTL1 &= ~UCTR;
                    UCB1CTL1 |= UCTXSTT;
                    if (i2c_in_buffer_size == 1) {
                        UCB1CTL1 |= UCTXNACK;
                    }
                } else {
                    UCB1CTL1 |= UCTXSTP;
                }
            }
            break;
        case 10: // Data received
            *i2c_in_buffer = UCB1RXBUF;
            i2c_in_buffer++;
            i2c_in_buffer_size--;
            if (i2c_in_buffer_size == 1) {
                UCB1CTL1 |= UCTXNACK;
            } else if (i2c_in_buffer_size == 0) {
                UCB1CTL1 |= UCTXSTP;
            }
            break;
    }
}