drivers/console/aarch64/skeleton_console.S

/*
 * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */
#include <asm_macros.S>

	/*
	 * This file contains a skeleton console implementation that can
	 * be used as basis for a real console implementation by platforms
	 * that do not contain PL011 hardware.
	 */

	.globl	console_core_init
	.globl	console_core_putc
	.globl	console_core_getc
	.globl	console_core_flush

	/* -----------------------------------------------
	 * int console_core_init(uintptr_t base_addr,
	 * unsigned int uart_clk, unsigned int baud_rate)
	 * Function to initialize the console without a
	 * C Runtime to print debug information. This
	 * function will be accessed by console_init and
	 * crash reporting.
	 * In: x0 - console base address
	 *     w1 - Uart clock in Hz
	 *     w2 - Baud rate
	 * Out: return 1 on success else 0 on error
	 * Clobber list : x1, x2
	 * -----------------------------------------------
	 */
func console_core_init
	/* Check the input base address */
	cbz	x0, core_init_fail
	/* Check baud rate and uart clock for sanity */
	cbz	w1, core_init_fail
	cbz	w2, core_init_fail
	/* Insert implementation here */
	mov	w0, #1
	ret
core_init_fail:
	mov	w0, wzr
	ret
endfunc console_core_init

	/* --------------------------------------------------------
	 * int console_core_putc(int c, uintptr_t base_addr)
	 * Function to output a character over the console. It
	 * returns the character printed on success or -1 on error.
	 * In : w0 - character to be printed
	 *      x1 - console base address
	 * Out : return -1 on error else return character.
	 * Clobber list : x2
	 * --------------------------------------------------------
	 */
func console_core_putc
	/* Check the input parameter */
	cbz	x1, putc_error
	/* Insert implementation here */
	ret
putc_error:
	mov	w0, #-1
	ret
endfunc console_core_putc

	/* ---------------------------------------------
	 * int console_core_getc(uintptr_t base_addr)
	 * Function to get a character from the console.
	 * It returns the character grabbed on success
	 * or -1 on error.
	 * In : x0 - console base address
	 * Clobber list : x0, x1
	 * ---------------------------------------------
	 */
func console_core_getc
	cbz	x0, getc_error
	/* Insert implementation here */
	ret
getc_error:
	mov	w0, #-1
	ret
endfunc console_core_getc

	/* ---------------------------------------------
	 * int console_core_flush(uintptr_t base_addr)
	 * Function to force a write of all buffered
	 * data that hasn't been output.
	 * In : x0 - console base address
	 * Out : return -1 on error else return 0.
	 * Clobber list : x0, x1
	 * ---------------------------------------------
	 */
func console_core_flush
	cbz	x0, flush_error
	/* Insert implementation here */
	mov	w0, #0
	ret
flush_error:
	mov	w0, #-1
	ret
endfunc console_core_flush