qmk_firmware/pjrc/usb_debug.c

#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;
}