common/console.c


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/*
 * console.c - the console dprintf writes to. semihosting SYS_WRITE0,
 * the firmware service on the qemu dev path, the arm64 stand-in for
 * the bios teletype the osdev loaders use. on real hardware this is
 * the one file that changes.
 *
 * Copyright (c) 2026 Bradley Morgan <brads@mainlining.org>
 *
 * 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 <sys/types.h>
#include <debug.h>
#include <semihosting.h>

/*
 * lk's _dprintf sink. printf buffers a line here then hands it to the
 * host, semihosting wants zero terminated strings not counts.
 */
#define TB_CONSOLE_MAX	256

static char console_buf[TB_CONSOLE_MAX];
static size_t console_len;

static void console_flush(void)
{
	if (console_len == 0)
		return;
	console_buf[console_len] = '\0';
	smh_write0(console_buf);
	console_len = 0;
}

void _putchar(char c)
{
	if (console_len >= TB_CONSOLE_MAX - 1)
		console_flush();
	if (c == '\n') {
		/* the host terminal wants cr lf, not lf alone */
		console_buf[console_len++] = '\r';
	}
	console_buf[console_len++] = c;
	if (c == '\n')
		console_flush();
}

int tb_console_init(void)
{
	/*
	 * the probe is one harmless call: SYS_GET_ERRNO with no file
	 * handle open. a host answers, bare metal ignores the trap.
	 */
	if (!smh_probe())
		return -1;
	console_len = 0;
	return 0;
}