Mini2440 UART原理及使用

// s3c24xx.h
// 2015.11.9

/* 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)

@******************************************************************************
@ head.S
@ 设置SDRAM，将程序复制到SDRAM，然后跳到SDRAM继续执行
@ 2015.11.9
@******************************************************************************       
   
.extern     main
.text 
.global _start 
_start:
Reset:                  
    ldr sp, =4096           
    bl  disable_watch_dog   
    bl  clock_init          @ 设置MPLL，改变FCLK、HCLK、PCLK
    bl  memsetup            
    bl  copy_steppingstone_to_sdram  
    ldr pc, =on_sdram                   
on_sdram:
    ldr sp, =0x34000000     
    ldr lr, =halt_loop      @ 设置返回地址，c程序执行完后pc指针会指向lr中的地址
    ldr pc, =main          
halt_loop:
    b   halt_loop

// init.c
// 2015.11.9

#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)
 *  S3C2410: 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, 0\n"        /* 读出控制寄存器 */ 
    "orr    r1, r1, #0xc0000000\n"          /* 设置为“asynchronous bus mode” */
    "mcr    p15, 0, r1, c1, c0, 0\n"        /* 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
// 2015.11.9

#include "s3c24xx.h"
#include "serial.h"

#define TXD0READY   (1<<2)
#define RXD0READY   (1)

#define PCLK            50000000    // init.c中的clock_init函数设置PCLK为50MHz
#define UART_CLK        PCLK        //  UART0的时钟源设为PCLK
#define UART_BAUD_RATE  115200      // 波特率
#define UART_BRD        ((UART_CLK  / (UART_BAUD_RATE * 16)) - 1)

// 115200,8N1,无流控
void uart0_init(void)
{
    GPHCON  |= 0xa0;    // GPH2,GPH3用作TXD0,RXD0，分别在位[5:4]，[7:6]，设为10使用该功能
    GPHUP   = 0x0c;     // GPH2,GPH3内部上拉

    ULCON0  = 0x03;     // 8N1(8个数据位，无较验，1个停止位)
    UCON0   = 0x05;     // 接收模式选择查询方式，UART时钟源为PCLK
    UFCON0  = 0x00;     // 不使用FIFO
    UMCON0  = 0x00;     // 不使用流控
    UBRDIV0 = UART_BRD; // 波特率为115200
}

void putc(unsigned char c)
{
    // 不断查询UTRSTAT0寄存器的位[2]，为1表示发送完毕
    while (!(UTRSTAT0 & TXD0READY));
    
    // 向UTXH0寄存器中写入数据，UART即自动将它发送出去
    UTXH0 = c;
}

unsigned char getc(void)
{
    // 不断查询UTRSTAT0寄存器的位[1]，为1表示接收缓冲区有数据
    while (!(UTRSTAT0 & RXD0READY));
    
    // 直接读取URXH0寄存器，即可获得接收到的数据
    return URXH0;
}

int isDigit(unsigned char c)
{
    if (c >= ‘0‘ && c <= ‘9‘)
        return 1;
    else
        return 0;       
}

int isLetter(unsigned char c)
{
    if (c >= ‘a‘ && c <= ‘z‘)
        return 1;
    else if (c >= ‘A‘ && c <= ‘Z‘)
        return 1;       
    else
        return 0;
}

// serial.h
// 2015.11.9

void uart0_init(void);
void putc(unsigned char c);
unsigned char getc(void);
int isDigit(unsigned char c);
int isLetter(unsigned char c);

// main.c
// 2015.11.9

#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;
}

/* uart.lds*/

SECTIONS {
    . = 0x30000000;
    .text          :   { *(.text) }            /*所有文件的代码段链接成一个.text的代码段*/
    .rodata ALIGN(4) : {*(.rodata)} 
    .data ALIGN(4) : { *(.data) }
    .bss ALIGN(4)  : { *(.bss)  *(COMMON) }
}

/*.bss段，链接完后，占用的内存释放，不同于.data段一直占有内存。
.bss这个节包含程序还未初始化的数据，当操作系统装入这个程序时将把这些变量都置为0。
使用.bss比使用.data的优势在于，bss节在编译后不占用磁盘的空间，这样编译、连接生成的代码的尺寸会比较小。
*/

objs := head.o init.o serial.o main.o

uart.bin: $(objs)
    arm-linux-ld -Tuart.lds -o uart_elf $^
    arm-linux-objcopy -O binary -S uart_elf $@
    arm-linux-objdump -D -m arm uart_elf > uart.dis
    
%.o:%.c
    arm-linux-gcc -Wall -O2 -c -o $@ $<

%.o:%.S
    arm-linux-gcc -Wall -O2 -c -o $@ $<

clean:
    rm -f uart.bin uart_elf uart.dis *.o