一文看懂Uart串口实验
时间：2019-01-18 09:08:01
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[导读]目的：在串口上输入一个字符，单板结合接收到后将它的ASCII值+1后，从串口输出。首先设置MPLL，提高系统时钟，令PCLK=50MHz，Uart选择PCLK为时钟源。然后代码复制到SDRAM中之后，
目的：在串口上输入一个字符，单板结合接收到后将它的ASCII值+1后，从串口输出。
首先设置MPLL，提高系统时钟，令PCLK=50MHz，Uart选择PCLK为时钟源。然后代码复制到SDRAM中之后，调用main函数。
uart.lds
SECTIONS {
. = 0x30000000;/*设置当前运行地址为0x30000000*/
.text : { *(.text) }/*所有输入文件的代码段*/
.rodata ALIGN(4) : {*(.rodata)} /*ALIGN(4)，表示运行地址4字节对齐。*/
.data ALIGN(4) : { *(.data) }
.bss ALIGN(4) : { *(.bss) *(COMMON) }
}Makefile
objs := head.o init.o serial.o main.o # $^ 代表所有的依赖文件。 $@--目标文件，$ uart.dis # -D：反汇编所有段 -m arm:指定反汇编文件使用arm架构 %.o:%.c arm-linux-gcc -Wall -O2 -c -o $@ $< #-Wall：打开警告信息 -O2：2级优化(常用) -c：只编译不连接 %.o:%.S arm-linux-gcc -Wall -O2 -c -o $@ $< clean: rm -f uart.bin uart_elf uart.dis *.o
head.S
@****************************************************************************** @ File：head.S @ 功能：设置SDRAM，将程序复制到SDRAM，然后跳到SDRAM继续执行 @****************************************************************************** .extern main .text .global _start _start: Reset: ldr sp, =4096 @ 设置栈指针，以下都是C函数，调用前需要设好栈 bl disable_watch_dog @ 关闭WATCHDOG，否则CPU会不断重启 @ bl是位置无关码，相当于：PCnew = PC + 偏移 = (4+8) + 0x28 = 0x34 @ 偏移值编译器算的，通过反汇编文件可查看 bl clock_init @ 设置MPLL，改变FCLK、HCLK、PCLK bl memsetup @ 设置存储控制器以使用SDRAM bl copy_steppingstone_to_sdram @ 复制代码到SDRAM中 ldr pc, =on_sdram @ 跳到SDRAM中继续执行 on_sdram: ldr sp, =0x34000000 @ 设置栈指针 ldr lr, =halt_loop @ 设置返回地址 ldr pc, =main @ 调用main函数 halt_loop: b halt_loop
init.c
/*
* init.c: 进行一些初始化
*/
#include "s3c24xx.h"
void disable_watch_dog(void);
void clock_init(void);
void memsetup(void);
void copy_steppingstone_to_sdram(void);
/*
* 关闭WATCHDOG，否则CPU会不断重启
*/
void disable_watch_dog(void)
{
WTCON = 0; // 关闭WATCHDOG很简单，往这个寄存器写0即可
}
#define S3C2410_MPLL_200MHZ ((0x5c<<12)|(0x04<<4)|(0x00))
#define S3C2440_MPLL_200MHZ ((0x5c<<12)|(0x01<<4)|(0x02))
/*
* 对于MPLLCON寄存器，[19:12]为MDIV，[9:4]为PDIV，[1:0]为SDIV
* 有如下计算公式：
* S3C2410: MPLL(FCLK) = (m * Fin)/(p * 2^s)
* S3C2440: MPLL(FCLK) = (2 * m * Fin)/(p * 2^s)
* 其中: m = MDIV + 8, p = PDIV + 2, s = SDIV
* 对于本开发板，Fin = 12MHz
* 设置CLKDIVN，令分频比为：FCLK:HCLK:PCLK=1:2:4，
* FCLK=200MHz,HCLK=100MHz,PCLK=50MHz
*/
void clock_init(void)
{
// LOCKTIME = 0x00ffffff; // 使用默认值即可
CLKDIVN = 0x03; // FCLK:HCLK:PCLK=1:2:4, HDIVN=1,PDIVN=1
/* 如果HDIVN非0，CPU的总线模式应该从“fast bus mode”变为“asynchronous bus mode” */
__asm__(
"mrc p15, 0, r1, c1, c0, 0n" /* 读出控制寄存器 */
"orr r1, r1, #0xc0000000n" /* 设置为“asynchronous bus mode” */
"mcr p15, 0, r1, c1, c0, 0n" /* 写入控制寄存器 */
);
/* 判断是S3C2410还是S3C2440 */
if ((GSTATUS1 == 0x32410000) || (GSTATUS1 == 0x32410002))
{
MPLLCON = S3C2410_MPLL_200MHZ; /* 现在，FCLK=200MHz,HCLK=100MHz,PCLK=50MHz */
}
else
{
MPLLCON = S3C2440_MPLL_200MHZ; /* 现在，FCLK=200MHz,HCLK=100MHz,PCLK=50MHz */
}
}
/*
* 设置存储控制器以使用SDRAM
*/
void memsetup(void)
{
volatile unsigned long *p = (volatile unsigned long *)MEM_CTL_BASE;
/* 这个函数之所以这样赋值，而不是像前面的实验(比如mmu实验)那样将配置值
* 写在数组中，是因为要生成”位置无关的代码”，使得这个函数可以在被复制到
* SDRAM之前就可以在steppingstone中运行
*/
/* 存储控制器13个寄存器的值 */
p[0] = 0x22011110; //BWSCON
p[1] = 0x00000700; //BANKCON0
p[2] = 0x00000700; //BANKCON1
p[3] = 0x00000700; //BANKCON2
p[4] = 0x00000700; //BANKCON3
p[5] = 0x00000700; //BANKCON4
p[6] = 0x00000700; //BANKCON5
p[7] = 0x00018005; //BANKCON6
p[8] = 0x00018005; //BANKCON7
/* REFRESH,
* HCLK=12MHz: 0x008C07A3,
* HCLK=100MHz: 0x008C04F4
*/
p[9] = 0x008C04F4;
p[10] = 0x000000B1; //BANKSIZE
p[11] = 0x00000030; //MRSRB6
p[12] = 0x00000030; //MRSRB7
}
void copy_steppingstone_to_sdram(void)
{
unsigned int *pdwSrc = (unsigned int *)0;
unsigned int *pdwDest = (unsigned int *)0x30000000;
while (pdwSrc < (unsigned int *)4096)
{
*pdwDest = *pdwSrc;
pdwDest++;
pdwSrc++;
}
}serial.c
#include "s3c24xx.h" #include "serial.h" #define TXD0READY (1<= '0' && c = 'a' && c = 'A' && c <= 'Z') return 1; else return 0; }
main.c
#include "serial.h"
int main()
{
unsigned char c;
uart0_init(); // 波特率115200，8N1(8个数据位，无校验位，1个停止位)
while(1)
{
// 从串口接收数据后，判断其是否数字或子母，若是则加1后输出
c = getc();
if (isDigit(c) || isLetter(c))
putc(c+1);
}
return 0;
}serial.h
void uart0_init(void); void putc(unsigned char c); unsigned char getc(void); int isDigit(unsigned char c); int isLetter(unsigned char c);
s3c24xx.h
/* WOTCH DOG register */ #define WTCON (*(volatile unsigned long *)0x53000000) /* SDRAM regisers */ #define MEM_CTL_BASE 0x48000000 #define SDRAM_BASE 0x30000000 /* NAND Flash registers */ #define NFCONF (*(volatile unsigned int *)0x4e000000) #define NFCMD (*(volatile unsigned char *)0x4e000004) #define NFADDR (*(volatile unsigned char *)0x4e000008) #define NFDATA (*(volatile unsigned char *)0x4e00000c) #define NFSTAT (*(volatile unsigned char *)0x4e000010) /*GPIO registers*/ #define GPBCON (*(volatile unsigned long *)0x56000010) #define GPBDAT (*(volatile unsigned long *)0x56000014) #define GPFCON (*(volatile unsigned long *)0x56000050) #define GPFDAT (*(volatile unsigned long *)0x56000054) #define GPFUP (*(volatile unsigned long *)0x56000058) #define GPGCON (*(volatile unsigned long *)0x56000060) #define GPGDAT (*(volatile unsigned long *)0x56000064) #define GPGUP (*(volatile unsigned long *)0x56000068) #define GPHCON (*(volatile unsigned long *)0x56000070) #define GPHDAT (*(volatile unsigned long *)0x56000074) #define GPHUP (*(volatile unsigned long *)0x56000078) /*UART registers*/ #define ULCON0 (*(volatile unsigned long *)0x50000000) #define UCON0 (*(volatile unsigned long *)0x50000004) #define UFCON0 (*(volatile unsigned long *)0x50000008) #define UMCON0 (*(volatile unsigned long *)0x5000000c) #define UTRSTAT0 (*(volatile unsigned long *)0x50000010) #define UTXH0 (*(volatile unsigned char *)0x50000020) #define URXH0 (*(volatile unsigned char *)0x50000024) #define UBRDIV0 (*(volatile unsigned long *)0x50000028) /*interrupt registes*/ #define SRCPND (*(volatile unsigned long *)0x4A000000) #define INTMOD (*(volatile unsigned long *)0x4A000004) #define INTMSK (*(volatile unsigned long *)0x4A000008) #define PRIORITY (*(volatile unsigned long *)0x4A00000c) #define INTPND (*(volatile unsigned long *)0x4A000010) #define INTOFFSET (*(volatile unsigned long *)0x4A000014) #define SUBSRCPND (*(volatile unsigned long *)0x4A000018) #define INTSUBMSK (*(volatile unsigned long *)0x4A00001c) /*external interrupt registers*/ #define EINTMASK (*(volatile unsigned long *)0x560000a4) #define EINTPEND (*(volatile unsigned long *)0x560000a8) /*clock registers*/ #define LOCKTIME (*(volatile unsigned long *)0x4c000000) #define MPLLCON (*(volatile unsigned long *)0x4c000004) #define UPLLCON (*(volatile unsigned long *)0x4c000008) #define CLKCON (*(volatile unsigned long *)0x4c00000c) #define CLKSLOW (*(volatile unsigned long *)0x4c000010) #define CLKDIVN (*(volatile unsigned long *)0x4c000014) /*PWM & Timer registers*/ #define TCFG0 (*(volatile unsigned long *)0x51000000) #define TCFG1 (*(volatile unsigned long *)0x51000004) #define TCON (*(volatile unsigned long *)0x51000008) #define TCNTB0 (*(volatile unsigned long *)0x5100000c) #define TCMPB0 (*(volatile unsigned long *)0x51000010) #define TCNTO0 (*(volatile unsigned long *)0x51000014) #define GSTATUS1 (*(volatile unsigned long *)0x560000B0)
[S3C2440链接脚本与位置无关码分析]
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