comm-bus-patterns

comm-bus-patterns

Knowledge Base

Production communication bus patterns for embedded C. STM32 HAL and LL examples.

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Pattern 1: I2C Register Read/Write for MEMS Sensors

Generic register-addressed I2C sensor driver (BME280, MPU-6050, etc.):

#define I2C_TIMEOUT_MS  5U

HAL_StatusTypeDef sensor_write_reg(I2C_HandleTypeDef *hi2c,
                                    uint8_t dev_addr, uint8_t reg, uint8_t val)
{
    uint8_t buf[2] = { reg, val };
    return HAL_I2C_Master_Transmit(hi2c, dev_addr << 1, buf, 2, I2C_TIMEOUT_MS);
}

HAL_StatusTypeDef sensor_read_reg(I2C_HandleTypeDef *hi2c,
                                   uint8_t dev_addr, uint8_t reg,
                                   uint8_t *out, uint16_t len)
{
    HAL_StatusTypeDef s;
    s = HAL_I2C_Master_Transmit(hi2c, dev_addr << 1, &reg, 1, I2C_TIMEOUT_MS);
    if (s != HAL_OK) { return s; }
    return HAL_I2C_Master_Receive(hi2c, (dev_addr << 1) | 1,
                                   out, len, I2C_TIMEOUT_MS);
}

/* I2C bus recovery: toggle SCL 9 times to release stuck SDA */
void i2c_bus_recover(GPIO_TypeDef *scl_port, uint16_t scl_pin,
                     GPIO_TypeDef *sda_port, uint16_t sda_pin)
{
    for (int i = 0; i < 9; i++) {
        HAL_GPIO_WritePin(scl_port, scl_pin, GPIO_PIN_SET);
        HAL_Delay(1);
        HAL_GPIO_WritePin(scl_port, scl_pin, GPIO_PIN_RESET);
        HAL_Delay(1);
    }
    /* Generate STOP: SDA low→high while SCL high */
    HAL_GPIO_WritePin(sda_port, sda_pin, GPIO_PIN_RESET);
    HAL_GPIO_WritePin(scl_port, scl_pin, GPIO_PIN_SET);
    HAL_Delay(1);
    HAL_GPIO_WritePin(sda_port, sda_pin, GPIO_PIN_SET);
}

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Pattern 2: SPI DMA Transfer with Semaphore

Non-blocking SPI using DMA and FreeRTOS binary semaphore for completion notification:

static SemaphoreHandle_t s_spi_done;

void HAL_SPI_TxRxCpltCallback(SPI_HandleTypeDef *hspi)
{
    if (hspi == &hspi1) {
        BaseType_t woken = pdFALSE;
        xSemaphoreGiveFromISR(s_spi_done, &woken);
        portYIELD_FROM_ISR(woken);
    }
}

void spi_dma_init(void)
{
    s_spi_done = xSemaphoreCreateBinary();
}

bool spi_transfer(const uint8_t *tx, uint8_t *rx, uint16_t len)
{
    spi_cs_assert();
    HAL_SPI_TransmitReceive_DMA(&hspi1, (uint8_t *)tx, rx, len);
    /* Block task until DMA complete (max 10ms) */
    bool ok = xSemaphoreTake(s_spi_done, pdMS_TO_TICKS(10)) == pdTRUE;
    spi_cs_deassert();
    return ok;
}