从2016年第一次接触rtthread，感觉很容易上手，记得一个项目是小飞行器上的IPC，趁着空闲，手里有一块jz2440的板子，准备在这块板子上跑起来rtthread，查了很多资料，最后决定自己写一个简单的BootLoader启动板子，启动rtthread系统。下面是简单的BootLoader源代码。

init.c

主要是内存控制器初始化、串口初始化及与串口相关函数实现、nandflash初始化及读写功能。

/* NAND FLASH控制器 */
#define NFCONF (*((volatile unsigned long *)0x4E000000))
#define NFCONT (*((volatile unsigned long *)0x4E000004))
#define NFCMMD (*((volatile unsigned char *)0x4E000008))
#define NFADDR (*((volatile unsigned char *)0x4E00000C))
#define NFDATA (*((volatile unsigned char *)0x4E000010))
#define NFSTAT (*((volatile unsigned char *)0x4E000020))

/* GPIO */
#define GPHCON              (*(volatile unsigned long *)0x56000070)
#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)

unsigned int *pGPFCON = (unsigned int *)0x56000050;
unsigned int *pGPFDAT = (unsigned int *)0x56000054;

void led_on(void)
{
    /* 配置GPF4为输出引脚 */
    *pGPFCON = 0x1500;
    /* 设置GPF4输出0 */
    *pGPFDAT = 0;    
}

void led_off(void)
{
    /* 配置GPF4为输出引脚 */
    *pGPFCON = 0x1500;
    /* 设置GPF4输出0 */
    *pGPFDAT = 0xff;    
}
#define TXD0READY   (1<<2)


void nand_read(unsigned int addr, unsigned char *buf, unsigned int len);

extern void puthex(unsigned int val);
extern void puts(char *str);
int isBootFromNorFlash(void)
{
    volatile int *p = (volatile int *)0;
    int val;

    val = *p;
    *p = 0x12345678;
    if (*p == 0x12345678)
    {
        /* 写成功, 是nand启动 */
        *p = val;
        return 0;
    }
    else
    {
        /* NOR不能像内存一样写 */
        return 1;
    }
}

void copy_code_to_sdram(unsigned char *src, unsigned char *dest, unsigned int len)
{    
    int i = 0;
    
    /* 如果是NOR启动 */
    if (isBootFromNorFlash())
    {
        while (i < len)
        {
            dest[i] = src[i];
            i++;
        }
    }
    else
    {
        //nand_init();
        nand_read((unsigned int)src, dest, len);
    }
}

void clear_bss(void)
{
    extern int __bss_start, __bss_end;
    int *p = &__bss_start;
    
    for (; p < &__bss_end; p++)
        *p = 0;
}

void nand_init(void)
{
#define TACLS   0
#define TWRPH0  1
#define TWRPH1  0
    /* 设置时序 */
    NFCONF = (TACLS<<12)|(TWRPH0<<8)|(TWRPH1<<4);
    /* 使能NAND Flash控制器, 初始化ECC, 禁止片选 */
    NFCONT = (1<<4)|(1<<1)|(1<<0);    
}

void nand_select(void)
{
    NFCONT &= ~(1<<1);    
}

void nand_deselect(void)
{
    NFCONT |= (1<<1);    
}

void nand_cmd(unsigned char cmd)
{
    volatile int i;
    NFCMMD = cmd;
    for (i = 0; i < 10; i++);
}

void nand_addr(unsigned int addr)
{
    unsigned int col  = addr % 2048;
    unsigned int page = addr / 2048;
    volatile int i;

    NFADDR = col & 0xff;
    for (i = 0; i < 10; i++);
    NFADDR = (col >> 8) & 0xff;
    for (i = 0; i < 10; i++);
    
    NFADDR  = page & 0xff;
    for (i = 0; i < 10; i++);
    NFADDR  = (page >> 8) & 0xff;
    for (i = 0; i < 10; i++);
    NFADDR  = (page >> 16) & 0xff;
    for (i = 0; i < 10; i++);    
}


void nand_wait_ready(void)
{
    while (!(NFSTAT & 1));
}

unsigned cha