| /************************************************************************** |
| * moxart/moxart_lowputc.S |
| * |
| * SPDX-License-Identifier: Apache-2.0 |
| * |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. The |
| * ASF licenses this file to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance with the |
| * License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| * License for the specific language governing permissions and limitations |
| * under the License. |
| * |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Included Files |
| **************************************************************************/ |
| |
| #include <nuttx/config.h> |
| |
| #include "chip.h" |
| |
| /************************************************************************** |
| * Pre-processor Definitions |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Private Types |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Private Function Prototypes |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Public Data |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Private Data |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Private Functions |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Public Functions |
| **************************************************************************/ |
| |
| /************************************************************************** |
| * Name: arm_lowputc |
| **************************************************************************/ |
| |
| /* This assembly language version has the advantage that it can does not |
| * require a C stack and uses only r0-r1. Hence it can be used during |
| * early boot phases. |
| */ |
| |
| .text |
| .global arm_lowputc |
| .type arm_lowputc, function |
| arm_lowputc: |
| /* On entry, r0 holds the character to be printed */ |
| |
| ldr r2, =UART0_BASE /* r2=UART0 base */ |
| |
| /* Poll bit 0 of the UART_SSR register. When the bit |
| * is clear, the TX FIFO is no longer full |
| */ |
| |
| 1: ldrb r1, [r2, #UART_LSR] |
| tst r1, #UART_LSR_THRE |
| beq 1b |
| |
| /* Send the character by writing it into the UART_THR |
| * register. |
| */ |
| |
| strb r0, [r2, #UART_THR] |
| |
| /* Wait for the tranmsit holding register (THR) to be |
| * emptied. This is determined when bit 6 of the LSR |
| * is set. |
| */ |
| |
| 2: ldrb r1, [r2, #UART_LSR] |
| tst r1, #UART_LSR_THRE |
| beq 2b |
| |
| /* If the character that we just sent was a linefeed, |
| * then send a carriage return as well. |
| */ |
| |
| teq r0, #'\n' |
| moveq r0, #'\r' |
| beq 1b |
| |
| /* And return */ |
| |
| mov pc, lr |
