STM32 - analog_mux_get_latest_val

/* analog_mux_get_latest_val
 * Created on: Jul 4, 2019
 * Author: Samuel Martel
 * Description: Gets the latest values from the 3 ADCs if the conversion on
 *              all of them is completed. If not, the function returns -1.
 *              After reading each value, it is shifted 4 bits to the left
 *              to convert it to an unsigned char (ADC values are 12bits).
 *              Then, each ADC is stopped, the is_ready flag is clear to allow
 *              a new conversion to be started.
 *              Finally, the index of the first value is calculated by
 *              converting its 2D ((x, y), ([0..19],[0..7])) to a 1D index that
 *              ranges from 0 to 160, the p_row and p_column pointers are set,
 *              and then the columns are shifted once.
 *              The index is then returned.
 * Params:  * unsigned char* f0 : pointer to the variable of the 1st value.
 *          * unsigned char* f1 : pointer to the variable of the 2nd value.
 *          * unsigned char* f2 : pointer to the variable of the 3rd value.
 *          * unsigned int* p_row : pointer to the variable of the current row.
 *          * unsigned int* p_column : pointer to the variable of the current
 *                                     column.
 * Return:  int : if error, -1. If successful, returns the current index.
 */
int analog_mux_get_latest_val(unsigned char* f0, unsigned char* f1,
        unsigned char* f2, unsigned int* p_row, unsigned int* p_column) {
    // If not ADCs are not ready to be read:
    if (!is_ready)
        // Return -1.
        return -1;

    // Read value from ADC 1.
    unsigned long val1 = HAL_ADC_GetValue(&hadc1);
    // Cast it to unsigned char.
    *f0 = (unsigned char) (val1 >> 4);

    // Read value from ADC 2.
    unsigned long val2 = HAL_ADC_GetValue(&hadc2);
    // Cast it to unsigned char.
    *f1 = (unsigned char) (val2 >> 4);

    // Read value from ADC 3.
    unsigned long val3 = HAL_ADC_GetValue(&hadc3);
    // Cast it to unsigned char.
    *f2 = (unsigned char) (val3 >> 4);

    // Stop the 3 ADCs.
    HAL_ADC_Stop_IT(&hadc1);
    HAL_ADC_Stop_IT(&hadc2);
    HAL_ADC_Stop_IT(&hadc3);

    // Clear flag to allow a new conversion to begin.
    is_ready = NOT_READY;

    // Calculate the index of the first value in the buffer.
    int idx = column + (row * 20);
    *p_row = row;
    *p_column = column;

    // Next set of rows.
    row++;
    // If every rows of the current column have been read:
    if (row >= 8) {
        // Reset the current row to 0.
        row = 0;
        // Shift to the next column.
        column = shift_shift_registers();
    }

    // Return the current index.
    return idx;
}