USART2->CR1 =
    USART_CR1_SBK        * 0 |    // Send Break
    USART_CR1_RWU        * 0 |    // Receiver wakeup
    USART_CR1_RE        * 1 |    // Receiver Enable
    USART_CR1_TE        * 1 |    // Transmitter Enable
    USART_CR1_IDLEIE    * 0 |    // IDLE Interrupt Enable
    USART_CR1_RXNEIE    * 1 |    // RXNE Interrupt Enable
    USART_CR1_TCIE        * 0 |    // Transmission Complete Interrupt Enable
    USART_CR1_TXEIE        * 0 |    // TE Interrupt Enable
    USART_CR1_PEIE        * 0 |    // PE Interrupt Enable
    USART_CR1_PS        * 0 |    // Parity Selection - Even
    USART_CR1_PCE        * 0 |    // Parity Control Enable
    USART_CR1_WAKE        * 0 |    // Wakeup method
    USART_CR1_M        * 0 |    // Word length: 1 Start bit, 8 Data bits, n Stop bit
    USART_CR1_UE        * 1 |    // USART Enable
    USART_CR1_OVER8        * 0;    // USART Oversampling by 8 enable

int uart_setup( // >0 - configured yet 0-service busy <0 - error
    char n,// which one
    baud_t baud, // may be long or int32
    char bits,      // ['5'..'9']
    char parity,  // ['E','O','N']
    char stops); // ['1','2']

usbd_device *usbd_init(const usbd_driver *driver,
               const struct usb_device_descriptor *dev,
               const struct usb_config_descriptor *conf,
               const char **strings, int num_strings,
               uint8_t *control_buffer, uint16_t control_buffer_size)
{
    usbd_device *usbd_dev;

    usbd_dev = driver->init();

    usbd_dev->driver = driver;
    usbd_dev->desc = dev;
    usbd_dev->config = conf;
    usbd_dev->strings = strings;
    usbd_dev->num_strings = num_strings;
    usbd_dev->ctrl_buf = control_buffer;
    usbd_dev->ctrl_buf_len = control_buffer_size;

    usbd_dev->user_callback_ctr[0][USB_TRANSACTION_SETUP] =
        _usbd_control_setup;
    usbd_dev->user_callback_ctr[0][USB_TRANSACTION_OUT] =
        _usbd_control_out;
    usbd_dev->user_callback_ctr[0][USB_TRANSACTION_IN] =
        _usbd_control_in;

    int i;
    for (i = 0; i < MAX_USER_SET_CONFIG_CALLBACK; i++) {
        usbd_dev->user_callback_set_config[i] = NULL;
    }

    return usbd_dev;
}

static void pre_main(void)
{
    /* Enable access to Floating-Point coprocessor. */
    SCB_CPACR |= SCB_CPACR_FULL * (SCB_CPACR_CP10 | SCB_CPACR_CP11);
}

"""Generate an nvic.h header from a small JSON file describing the interrupt
numbers.

Code generation is chosen here because the resulting C code needs to be very
repetetive (definition of the IRQ numbers, function prototypes, weak fallback
definition and vector table definition), all being very repetitive. No portable
method to achive the same thing with C preprocessor is known to the author.
(Neither is any non-portable method, for that matter.)"""