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我正在尝试使用 printf 格式化通过 USB UART 发送的数据，它给了我垃圾。我可以发送一个简单的字符串并且可以正常工作，但是我尝试格式化的任何内容都会产生垃圾。查看代码我认为这与我的字符串不在程序空间中有关，但我不确定。

这是我的主要内容：

void main(void) {
    CPU_PRESCALE(CPU_16MHz);
    init_uart();

    int degree = 0;
    char buffer[50];

    while(1) {
        degree = (degree + 1) % 360;

        send_str(PSTR("\n\nHello!!!\n\n"));
        memset(buffer, 0, 50);
        sprintf_P(buffer, PSTR("%d degrees\n"), degree);
        send_str(buffer);

        _delay_ms(20);
    }
}

输出如下所示：

Hello!!!

����/�������(/����#Q��������

Hello!!!

����/�������(/����#Q��������

我在教程中找到的 USB UART 代码。相关部分如下所示：

void send_str(const char *s)
{
    char c;
    while (1) {
        c = pgm_read_byte(s++);
        if (!c) break;
        usb_serial_putchar(c);
    }
}

int8_t usb_serial_putchar(uint8_t c)
{
    uint8_t timeout, intr_state;

    // if we're not online (enumerated and configured), error
    if (!usb_configuration) return -1;
    // interrupts are disabled so these functions can be
    // used from the main program or interrupt context,
    // even both in the same program!
    intr_state = SREG;
    cli();
    UENUM = CDC_TX_ENDPOINT;
    // if we gave up due to timeout before, don't wait again
    if (transmit_previous_timeout) {
        if (!(UEINTX & (1<<RWAL))) {
            SREG = intr_state;
            return -1;
        }
        transmit_previous_timeout = 0;
    }
    // wait for the FIFO to be ready to accept data
    timeout = UDFNUML + TRANSMIT_TIMEOUT;
    while (1) {
        // are we ready to transmit?
        if (UEINTX & (1<<RWAL)) break;
        SREG = intr_state;
        // have we waited too long?  This happens if the user
        // is not running an application that is listening
        if (UDFNUML == timeout) {
            transmit_previous_timeout = 1;
            return -1;
        }
        // has the USB gone offline?
        if (!usb_configuration) return -1;
        // get ready to try checking again
        intr_state = SREG;
        cli();
        UENUM = CDC_TX_ENDPOINT;
    }
    // actually write the byte into the FIFO
    UEDATX = c;
    // if this completed a packet, transmit it now!
    if (!(UEINTX & (1<<RWAL))) UEINTX = 0x3A;
    transmit_flush_timer = TRANSMIT_FLUSH_TIMEOUT;
    SREG = intr_state;
    return 0;
}
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