TQ2440裸板学习笔记7--串口

串口时钟使用了PCLK，所以在初始化串口之前需要先将系统时钟初始化，(除非想一直使用默认时钟)。

一、代码

1. start.S 主要功能是：

     a.关闭看门狗

     b. 初始化系统时钟

     c. 设置堆栈

     d. 跳到main函数

.text
.global _start
_start:
    /*disable watchdog*/
    ldr r0, =0x53000000
    mov r1, #0x0
    str r1, [r0]

#define COCKTIME    0x4C000000
#define MPLLCON        0x4C000004
#define UPLLCON        0x4C000008
#define CLKCON        0x4C00000C
#define CLKSLOW        0x4C000010
#define CLKDIVN     0x4C000014
#define CAMDIVN     0x4C000018
    /*FCLK:HCLK:PCLK=1:4:8*/
    ldr r0, =CLKDIVN
    mov r1, #0x05
    str r1, [r0]

    mrc p15, 0, r0, c1, c0, 0
    orr r0, r0, #0xc0000000
    mcr p15, 0, r0, c1, c0,0

    /*MPLL=(2*m*Fin)/(P*(1<<S)), m=(MDIV+8), p=PDIV+2 s=SDIV*/
    ldr r0, =MPLLCON
    ldr r1, =((0x5C<<12)|(0x01<<4)|(0x01))
    str r1, [r0]

    ldr r0, =0x10000
1:
    sub r0, r0, #1
    bne 1b

    /*UPLL=(m*Fin)/(P*(1<<S)), m=(MDIV+8), p=(PDIV+2), s=SDIV*/
    ldr r0, =UPLLCON
    ldr r1, =((0x10<<12)|(0x01<<4)|(0x01))
    str r1, [r0]

    ldr r0, =0x10000
1:
    sub r0, r0, #1
    bne 1b

    /* set up the stack    */
    ldr sp, =1024*4
    bl main

loop:
    b loop

2. main.c 主要功能是：

a. 初始化串口

b. 进入死循环，每次点亮一个led灯，顺便打印一个字母'a'

#include "uart.h"
#define GPBCON (*(volatile unsigned int *) 0x56000010)
#define GPBDAT (*(volatile unsigned int *) 0x56000014)

static inline void delay (unsigned long loops)
{
    __asm__ volatile ("1:\n"
            "subs %0, %1, #1\n"
            "bne 1b":"=r" (loops):"0" (loops));
}

void main()
{
    int i = 1;
    GPBCON = 0x15400;
    init_uart();
    while(1)
    {
        GPBDAT = 0x7FF&(~i<<5);
        i *= 2;
        if(16==i)
            i = 1;
        delay(400000);
        putc('a');
    }
    return ;
}

3.uart.c 主要功能：

a. 初始化串口

b. 实现发送与接收函数getc与putc

#define GPHCON (* (volatile unsigned int *) 0x56000070)
#define GPHUP (* (volatile unsigned int *) 0x56000078)

#define ULCON0 (* (volatile unsigned int *) 0x50000000)
#define UCON0 (* (volatile unsigned int *) 0x50000004)
#define UFCON0 (* (volatile unsigned int *) 0x50000008)
#define UMCON0 (* (volatile unsigned int *) 0x5000000C)
#define UTRSTAT0 (* (volatile unsigned int *) 0x50000010)
#define UERSTAT0 (* (volatile unsigned int *) 0x50000014)
#define UFSTAT0 (* (volatile unsigned int *) 0x50000018)
#define UMSTAT0 (* (volatile unsigned int *) 0x5000001C)
#define UTXH0 (* (volatile unsigned char *) 0x50000020)
#define URXH0 (* (volatile unsigned char *) 0x50000024)
#define UBRDIV0 (* (volatile unsigned int *) 0x50000028)

#define BAUD_RATE 115200

void uart_init(void)
{
    GPHCON = 0x000000A0;
    GPHUP = 0x000007FF;
    ULCON0 = (0x03); //8N1
    UCON0 = (0x01<<2)|(0x01);
    UFCON0 = 0;
    UMCON0 = 0;
    UBRDIV0 = (int)((50*1000*1000)/(BAUD_RATE*16))-1;
}

unsigned char uart_getc(void)
{
    while(!(UTRSTAT0 & 0x01))
        ;
    return (URXH0 & 0xff);
}

void uart_putc(char c)
{
    while (!(UTRSTAT0&0x02))
        ;
    UTXH0 = c;
    if('\n' == c)
        uart_putc('\r');
}

void uart_puts(char *s)
{
    while (*s)
    {
        uart_putc(*s++);
    }
}

注: uart.c中的uart_putc函数(ascii中: \n__换行__LF__0x10   \r__回车__CR__0x13 )

1. 当键盘敲下 Enter键时，从串口收到的按键是0x0d(即:\r 回车符:将光标移动到行首，而不换行)。

2. 当调用puts("hello\n");时putc收到\n后，将换行但光标的列不变，然后再输出\r，将光标移动到换行之后的行首，这样效果就跟平常的回车一样了。

4. uart.h

void uart_init(void);
unsigned char uart_getc(void);
void uart_putc(char c);

编译时只需要在Makefile的OBJS中添加uart.o就可以了。

二、测试一下getc函数

2.1 将main中主循环改为接收一个字符然后打印

uart_init();
while(1)
    {
        c=uart_getc();
        uart_putc(c);
    }