trezor-firmware/micropython/firmware/mphalport.c

#include "py/mphal.h"

void USBD_CDC_TxAlways(const uint8_t *buf, uint32_t len);
int USBD_CDC_Rx(uint8_t *buf, uint32_t len, uint32_t timeout);

int mp_hal_stdin_rx_chr(void) {
    for (;;) {
        byte c;
        if (USBD_CDC_Rx(&c, 1, 0) != 0) {
            return c;
        }
    }
}

void mp_hal_stdout_tx_strn(const char *str, size_t len) {
    USBD_CDC_TxAlways((const uint8_t*)str, len);
}