I2C 드라이버 구현 — Master·7-bit/10-bit·Clock Stretching 처리

1
Standard mode (100 kHz):
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CCR = PCLK / (2 × 100000)
3

4
Fast mode (400 kHz):
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CCR = PCLK / (3 × 400000)   (DUTY=0)
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CCR = PCLK / (25 × 400000)  (DUTY=1)
7

8
TRISE = (PCLK / 1MHz) + 1    (standard)
9
TRISE = (PCLK × 0.3) + 1     (fast)

1
void i2c_init_400k(void) {
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    RCC->APB1ENR |= RCC_APB1ENR_I2C1EN;
3
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN;
4

5
    // PB8 SCL, PB9 SDA (AF4, open-drain, no pull — 외부 4.7k pull-up)
6
    gpio_init(GPIOB, 8, &(gpio_config_t){.mode=GPIO_MODE_AF, .otype=GPIO_OTYPE_OD,
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                                          .speed=GPIO_SPEED_MED, .af=4});
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    gpio_init(GPIOB, 9, &(gpio_config_t){.mode=GPIO_MODE_AF, .otype=GPIO_OTYPE_OD,
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                                          .speed=GPIO_SPEED_MED, .af=4});
10

11
    I2C1->CR1 = I2C_CR1_SWRST;
12
    I2C1->CR1 = 0;
13

14
    I2C1->CR2   = 42u;             // PCLK1 = 42 MHz
15
    I2C1->CCR   = I2C_CCR_FS | 35; // fast mode, 400 kHz
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    I2C1->TRISE = 13;
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    I2C1->CR1   = I2C_CR1_PE;       // enable
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}

1
#define I2C_TIMEOUT_MS 50
2

3
static int wait_flag(volatile uint32_t *reg, uint32_t mask, int set) {
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    uint32_t start = millis();
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    while (((*reg & mask) != 0) != set) {
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        if (millis() - start > I2C_TIMEOUT_MS) return -1;
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    }
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    return 0;
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}
10

11
int i2c_write(uint8_t addr7, const uint8_t *data, size_t n) {
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    // START
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    I2C1->CR1 |= I2C_CR1_START;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_SB, 1)) return -1;
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16
    // SLA+W
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    I2C1->DR = (addr7 << 1) | 0;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_ADDR, 1)) {
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        I2C1->CR1 |= I2C_CR1_STOP;
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        return -2;   // NACK or bus error
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    }
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    (void)I2C1->SR1; (void)I2C1->SR2;   // clear ADDR
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    // DATA bytes
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    for (size_t i = 0; i < n; i++) {
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        if (wait_flag(&I2C1->SR1, I2C_SR1_TXE, 1)) goto err;
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        I2C1->DR = data[i];
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    }
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    if (wait_flag(&I2C1->SR1, I2C_SR1_BTF, 1)) goto err;
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    // STOP
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    I2C1->CR1 |= I2C_CR1_STOP;
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    return 0;
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35
err:
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    I2C1->CR1 |= I2C_CR1_STOP;
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    return -3;
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}

1
int i2c_read_reg(uint8_t addr7, uint8_t reg, uint8_t *buf, size_t n) {
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    if (n == 0) return 0;
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4
    // === Phase 1: write reg address ===
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    I2C1->CR1 |= I2C_CR1_START;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_SB, 1)) return -1;
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    I2C1->DR = (addr7 << 1) | 0;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_ADDR, 1)) goto stop;
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    (void)I2C1->SR1; (void)I2C1->SR2;
11

12
    if (wait_flag(&I2C1->SR1, I2C_SR1_TXE, 1)) goto stop;
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    I2C1->DR = reg;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_BTF, 1)) goto stop;
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16
    // === Phase 2: repeated START + read ===
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    I2C1->CR1 |= I2C_CR1_START;
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    if (wait_flag(&I2C1->SR1, I2C_SR1_SB, 1)) goto stop;
19

20
    I2C1->DR = (addr7 << 1) | 1;
21

22
    if (n == 1) {
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        I2C1->CR1 &= ~I2C_CR1_ACK;       // NACK after first byte
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        if (wait_flag(&I2C1->SR1, I2C_SR1_ADDR, 1)) goto stop;
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        (void)I2C1->SR1; (void)I2C1->SR2;
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        I2C1->CR1 |= I2C_CR1_STOP;
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        if (wait_flag(&I2C1->SR1, I2C_SR1_RXNE, 1)) return -1;
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        buf[0] = I2C1->DR;
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    } else {
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        I2C1->CR1 |= I2C_CR1_ACK;
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        if (wait_flag(&I2C1->SR1, I2C_SR1_ADDR, 1)) goto stop;
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        (void)I2C1->SR1; (void)I2C1->SR2;
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        for (size_t i = 0; i < n; i++) {
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            if (i == n - 1) {
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                I2C1->CR1 &= ~I2C_CR1_ACK;
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                I2C1->CR1 |= I2C_CR1_STOP;
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            }
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            if (wait_flag(&I2C1->SR1, I2C_SR1_RXNE, 1)) return -1;
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            buf[i] = I2C1->DR;
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        }
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    }
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    return 0;
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45
stop:
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    I2C1->CR1 |= I2C_CR1_STOP;
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    return -2;
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}

1
void i2c_bus_recover(void) {
2
    // SCL/SDA를 GPIO output으로 임시 전환
3
    gpio_init(GPIOB, 8, &(gpio_config_t){.mode=GPIO_MODE_OUTPUT, .otype=GPIO_OTYPE_OD});
4
    gpio_init(GPIOB, 9, &(gpio_config_t){.mode=GPIO_MODE_INPUT, .pull=GPIO_PULL_UP});
5

6
    for (int i = 0; i < 9; i++) {
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        GPIOB->BSRR = (1u << (8 + 16)); delay_us(5);
8
        GPIOB->BSRR = (1u << 8);        delay_us(5);
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        if (GPIOB->IDR & (1u << 9)) break;   // SDA released
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    }
11

12
    // STOP manually: SDA low → SCL high → SDA high
13
    gpio_init(GPIOB, 9, &(gpio_config_t){.mode=GPIO_MODE_OUTPUT, .otype=GPIO_OTYPE_OD});
14
    GPIOB->BSRR = (1u << (9 + 16)); delay_us(5);
15
    GPIOB->BSRR = (1u << 8);        delay_us(5);
16
    GPIOB->BSRR = (1u << 9);        delay_us(5);
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18
    // Back to AF
19
    gpio_init(GPIOB, 8, &(gpio_config_t){.mode=GPIO_MODE_AF, .otype=GPIO_OTYPE_OD, .af=4});
20
    gpio_init(GPIOB, 9, &(gpio_config_t){.mode=GPIO_MODE_AF, .otype=GPIO_OTYPE_OD, .af=4});
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22
    I2C1->CR1 |= I2C_CR1_SWRST;
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    I2C1->CR1 = 0;
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    i2c_init_400k();
25
}