Snippet of code which generates a random number using the MSPM0+ TRNG module

gistfile1.txt

__STATIC_INLINE void update_reg(
    volatile uint32_t *reg, uint32_t val, uint32_t mask)
{
    uint32_t tmp;

    tmp  = *reg;
    tmp  = tmp & ~mask;
    *reg = tmp | (val & mask);
}

uint32_t GenerateRandomNumber()
{
    int randomNumber = 0;
    // Power on and initialize TRNG
    TRNG->GPRCM.RSTCTL = TRNG_RSTCTL_RESETASSERT_ASSERT | TRNG_RSTCTL_KEY_UNLOCK_W;
    TRNG->GPRCM.PWREN = TRNG_PWREN_KEY_UNLOCK_W | TRNG_PWREN_ENABLE_ENABLE;
    delay_cycles(POWER_STARTUP_DELAY);

    TRNG->CLKDIVIDE = (uint32_t) TRNG_CLKDIVIDE_RATIO_DIV_BY_2;

    // Send "Normal Function" command and then wait for it to complete
    update_reg(&TRNG->CTL, (uint32_t) TRNG_CTL_CMD_NORM_FUNC, TRNG_CTL_CMD_MASK);
    while (!((TRNG->CPU_INT.RIS & TRNG_RIS_IRQ_CMD_DONE_MASK) ==
            TRNG_RIS_IRQ_CMD_DONE_SET));
    TRNG->CPU_INT.ICLR = TRNG_IMASK_IRQ_CMD_DONE_MASK; // clear interrupt status

    update_reg(&TRNG->CTL,
        ((uint32_t) 0x3 << TRNG_CTL_DECIM_RATE_OFS), // set clock to decimate by 4
        TRNG_CTL_DECIM_RATE_MASK);

    /* Setup and start a capture, then wait for the result */
    while (!((TRNG->CPU_INT.RIS & TRNG_RIS_IRQ_CAPTURED_RDY_MASK) ==
            TRNG_RIS_IRQ_CAPTURED_RDY_SET));
    TRNG->CPU_INT.ICLR = TRNG_IMASK_IRQ_CAPTURED_RDY_MASK; // clear interrupt status
    randomNumber = TRNG->DATA_CAPTURE; // here is our random number!!!

    /* Power off the TRNG peripheral */
    TRNG->GPRCM.PWREN = TRNG_PWREN_KEY_UNLOCK_W | TRNG_PWREN_ENABLE_DISABLE;
}

The technical reference manual also suggests a number of tests after power on before trying to generate!