【RISC-V设计-14】- RISC-V处理器设计K0A之打印输出

【RISC-V设计-14】- RISC-V处理器设计K0A之打印输出

1.简介

本文将详细阐述如何利用 printf 来打印字符串，在此过程中使用了一个开源的库 xprintf 。xprintf 是一个紧凑的字符串 I/O 库，它非常适用于程序存储器不足以用于常规 printf 函数的微型微控制器。通过调用 xprintf 函数成功输出了“Hello RISC-V World!”，同时还对该库的使用方法以及如何进行编译等内容加以介绍。xprintf库的地址为：http://elm-chan.org/fsw/strf/xprintf.html，下载后使将使用xprintf.c和xprintf.h两个文件。

2.验证用例

// -------------------------------------------------------------------------------------------------
// Copyright 2024 Kearn Chen, [e-mail]
//
// Licensed 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.
// -------------------------------------------------------------------------------------------------
// Description :
//             1. Run Hello World!
// -------------------------------------------------------------------------------------------------task initcase;load_instr("hello_world_test/hello_world_test.bin");endtasktask testcase;#2_000_000;endtask

在验证用例中，任务initcase加载Bin文件到仿真模型中，任务testcase延迟2毫秒，等待CPU执行完软件指令。

3.软件代码

// -------------------------------------------------------------------------------------------------
// Copyright 2024 Kearn Chen, [e-mail]
//
// Licensed 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.
// -------------------------------------------------------------------------------------------------#include "xprintf.h"void xfunc_output_callback(int c)
{*((volatile unsigned int *)0xc0000) = c;
}void simulation_finish(void)
{*((volatile unsigned int *)0xc0004) = 0x12345678;
}int main(void)
{xfunc_output = xfunc_output_callback;xprintf("Hello RISC-V World!\n");simulation_finish();while(1);
}

上述代码中，首先是初始化打印输出的回调函数，在回调函数中，将要输出的字符写入地址0xc0000寄存器中，这个寄存器在之前的文章【RISC-V设计-12】- RISC-V处理器设计K0A之验证环境中第4部分有描述，写入此寄存器的数据会存入到一个队列里面，在遇到输出字符为\n时，将整个队列内的输出到终端。在输出完字符后，调用simulation_finish函数，仿真运行结束。在xprintf库中，有一些宏定义，如下所示，根据需要可以打开和关闭。

#define XF_USE_OUTPUT	1	/* 1: Enable output functions */
#define	XF_CRLF			0	/* 1: Convert \n ==> \r\n in the output char */
#define	XF_USE_DUMP		0	/* 1: Enable put_dump function */
#define	XF_USE_LLI		0	/* 1: Enable long long integer in size prefix ll */
#define	XF_USE_FP		0	/* 1: Enable support for floating point in type e and f */
#define XF_DPC			'.'	/* Decimal separator for floating point */
#define XF_USE_INPUT	0	/* 1: Enable input functions */
#define	XF_INPUT_ECHO	0	/* 1: Echo back input chars in xgets function */

4.链接脚本

ENTRY( _start )__stack_size = 2048;PROVIDE( _stack_size = __stack_size );MEMORY
{ROM (rx)  : ORIGIN = 0x00000, LENGTH = 512KRAM (xrw) : ORIGIN = 0x80000, LENGTH = 256K
}SECTIONS
{.init :{_sinit = .;. = ALIGN(4);KEEP(*(SORT_NONE(.init))). = ALIGN(4);_einit = .;} >ROM.text :{. = ALIGN(4);*(.text)*(.text.*)*(.rodata)*(.rodata*)*(.gnu.linkonce.t.*). = ALIGN(4);} >ROM.fini :{KEEP(*(SORT_NONE(.fini))). = ALIGN(4);} >ROMPROVIDE( _etext = . );PROVIDE( _eitcm = . );  .preinit_array :{PROVIDE_HIDDEN (__preinit_array_start = .);KEEP (*(.preinit_array))PROVIDE_HIDDEN (__preinit_array_end = .);} >ROM.init_array :{PROVIDE_HIDDEN (__init_array_start = .);KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))PROVIDE_HIDDEN (__init_array_end = .);} >ROM.fini_array :{PROVIDE_HIDDEN (__fini_array_start = .);KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors))PROVIDE_HIDDEN (__fini_array_end = .);} >ROM.ctors :{KEEP (*crtbegin.o(.ctors))KEEP (*crtbegin?.o(.ctors))KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))KEEP (*(SORT(.ctors.*)))KEEP (*(.ctors))} >ROM.dtors :{KEEP (*crtbegin.o(.dtors))KEEP (*crtbegin?.o(.dtors))KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))KEEP (*(SORT(.dtors.*)))KEEP (*(.dtors))} >ROM.dalign :{. = ALIGN(4);PROVIDE(_data_vma = .);} >RAM AT>ROM  .dlalign :{. = ALIGN(4); PROVIDE(_data_lma = .);} >ROM.data :{. = ALIGN(4);*(.gnu.linkonce.r.*)*(.data .data.*)*(.gnu.linkonce.d.*). = ALIGN(8);PROVIDE( __global_pointer$ = . + 0x800 );*(.sdata .sdata.*)*(.sdata2*)*(.gnu.linkonce.s.*). = ALIGN(8);*(.srodata.cst16)*(.srodata.cst8)*(.srodata.cst4)*(.srodata.cst2)*(.srodata .srodata.*). = ALIGN(4);PROVIDE( _edata = .);} >RAM AT>ROM.bss :{. = ALIGN(4);PROVIDE( _sbss = .);*(.sbss*)*(.gnu.linkonce.sb.*)*(.bss*)*(.gnu.linkonce.b.*)    *(COMMON*). = ALIGN(4);PROVIDE( _ebss = .);} >RAM AT>ROMPROVIDE( _end = _ebss);PROVIDE( end = . );.stack ORIGIN(RAM) + LENGTH(RAM) - __stack_size :{PROVIDE( _heap_end = . );. = ALIGN(4);PROVIDE(_susrstack = . );. = . + __stack_size;PROVIDE( _eusrstack = .);} >RAM 
}

5.编译脚本

# -------------------------------------------------------------------------------------------------
# Copyright 2024 Kearn Chen, [e-mail]
#
# Licensed 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.
# -------------------------------------------------------------------------------------------------PREFIX := riscv-none-embed-LINKER := ../common/link.ldOBJECT += ../common/startup.o
OBJECT += ../common/xprintf.o
OBJECT += main.oCFLAGS := -march=rv32e -mabi=ilp32e -I../commonLFLAGS := -march=rv32e -mabi=ilp32e -T$(LINKER) -nostartfilesTARGET := $(notdir $(shell pwd))all : $(TARGET).asm $(TARGET).bin%.bin : %.elf$(PREFIX)objcopy -Obinary $< $@%.asm : %.elf$(PREFIX)objdump -D $< > $@%.elf : $(OBJECT)$(PREFIX)gcc $(LFLAGS) -o $@ $^$(PREFIX)size $@%.o : %.S$(PREFIX)gcc $(CFLAGS) -c -o $@ $<%.o : %.c$(PREFIX)gcc $(CFLAGS) -c -o $@ $<clean :@rm -rf *.o *.elf *.asm *.bin ../common/*.o.PHONY: clean all.SECONDARY:

上述脚本中所使用的startup.o文件为startup.S文件所编译产生，这个文件在之前的文章【RISC-V设计-09】- RISC-V处理器设计K0A之CIC中第5部分已有介绍，这个文件为RISCV-K0A的启动文件，同时还具有中断处理的功能。编译结果如下

riscv-none-embed-gcc -march=rv32e -mabi=ilp32e -I../common -c -o ../common/startup.o ../common/startup.S
riscv-none-embed-gcc -march=rv32e -mabi=ilp32e -I../common -c -o ../common/xprintf.o ../common/xprintf.c
riscv-none-embed-gcc -march=rv32e -mabi=ilp32e -I../common -c -o main.o main.c
riscv-none-embed-gcc -march=rv32e -mabi=ilp32e -T../common/link.ld -nostartfiles -o hello_world_test.elf ../common/startup.o ../common/xprintf.o main.o
riscv-none-embed-size hello_world_test.elftext	   data	    bss	    dec	    hex	filename3164	      0	   2056	   5220	   1464	hello_world_test.elf
riscv-none-embed-objdump -D hello_world_test.elf > hello_world_test.asm
riscv-none-embed-objcopy -Obinary hello_world_test.elf hello_world_test.bin

6.仿真结果

6.1 复位结束

6.2 运行成功

6.3 终端打印

*Verdi* FSDB WARNING: The FSDB file already exists. Overwriting the FSDB file may crash the programs that are using this file.
*Verdi* : Create FSDB file 'novas.fsdb'
*Verdi* : Begin traversing the scopes, layer (0).
*Verdi* : End of traversing.
[MCU_INFO] : Hello RISC-V World!
$finish called from file "../env/slave_model.v", line 136.
$finish at simulation time                43210

7.总结

本文介绍了如何在RISCV-K0A上使用xprintf库文件，并通过xprintf输出了"Hello RISC-V World!"到终端显示。