qmk_firmware/tmk_core/protocol/pjrc/usb_debug.c

/* USB Keyboard Plus Debug Channel Example for Teensy USB Development Board
 * http://www.pjrc.com/teensy/usb_keyboard.html
 * Copyright (c) 2009 PJRC.COM, LLC
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <avr/interrupt.h>
#include "sendchar.h"
#include "usb_debug.h"

// the time remaining before we transmit any partially full
// packet, or send a zero length packet.
volatile uint8_t debug_flush_timer = 0;

int8_t sendchar(uint8_t c) {
    static uint8_t previous_timeout = 0;
    uint8_t        timeout, intr_state;

    // if we're not online (enumerated and configured), error
    if (!usb_configured()) 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 = DEBUG_TX_ENDPOINT;
    // if we gave up due to timeout before, don't wait again
    if (previous_timeout) {
        if (!(UEINTX & (1 << RWAL))) {
            SREG = intr_state;
            return -1;
        }
        previous_timeout = 0;
    }
    // wait for the FIFO to be ready to accept data
    timeout = UDFNUML + 4;
    while (1) {
        // are we ready to transmit?
        if (UEINTX & (1 << RWAL)) break;
        SREG = intr_state;
        // have we waited too long?
        if (UDFNUML == timeout) {
            previous_timeout = 1;
            return -1;
        }
        // has the USB gone offline?
        if (!usb_configured()) return -1;
        // get ready to try checking again
        intr_state = SREG;
        cli();
        UENUM = DEBUG_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;
        debug_flush_timer = 0;
    } else {
        debug_flush_timer = 2;
    }
    SREG = intr_state;
    return 0;
}

// immediately transmit any buffered output.
void usb_debug_flush_output(void) {
    uint8_t intr_state;

    intr_state = SREG;
    cli();
    if (debug_flush_timer) {
        UENUM = DEBUG_TX_ENDPOINT;
        while ((UEINTX & (1 << RWAL))) {
            UEDATX = 0;
        }
        UEINTX            = 0x3A;
        debug_flush_timer = 0;
    }
    SREG = intr_state;
}