Write the bootloader yourself ------ write the first stage

content

1. The role of bootloader

2. Write the code

2.1 start.S

2.2 boot.lds link script

2.3 init.c

2.3.1 nand_init

2.3.2 nand_read

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1. The role of bootloader

The goal of the bootloader: start the kernel ,

2. Write the code

2.1 start.S

#define S3C2440_MPLL_200MHZ     ((0x5c<<12)|(0x01<<4)|(0x02))
#define MEM_CTL_BASE    0x48000000

.text
.global _start
_start:

/* 1. 关看门狗 */
	ldr r0, =0x53000000
	mov r1, #0
	str r1, [r0]

/* 2. 设置时钟 */
	ldr r0, =0x4c000014
	mov r1, #0x03;            // FCLK:HCLK:PCLK=1:2:4, HDIVN=1,PDIVN=1
	str r1, [r0]

	/* 如果HDIVN非0，CPU的总线模式应该从“fast bus mode”变为“asynchronous bus mode” */
	mrc	p15, 0, r1, c1, c0, 0		/* 读出控制寄存器 */ 
	orr	r1, r1, #0xc0000000			/* 设置为“asynchronous bus mode” */
	mcr	p15, 0, r1, c1, c0, 0		/* 写入控制寄存器 */

	/* MPLLCON = S3C2440_MPLL_200MHZ */
	ldr r0, =0x4c000004
	ldr r1, =S3C2440_MPLL_200MHZ
	str r1, [r0]

/* 3. 初始化SDRAM */
	ldr r0, =MEM_CTL_BASE
	adr r1, sdram_config     /* sdram_config的当前地址 */
	add r3, r0, #(13*4)
1:
	ldr r2, [r1], #4
	str r2, [r0], #4
	cmp r0, r3
	bne 1b

/* 4. 重定位 : 把bootloader本身的代码从flash复制到它的链接地址去 */
	ldr sp, =0x34000000

	bl nand_init

	mov r0, #0
	ldr r1, =_start
	ldr r2, =__bss_start
	sub r2, r2, r1
	
	bl copy_code_to_sdram
	bl clear_bss
	
/* 5. 执行main */
	ldr lr, =halt
	ldr pc, =main
halt:
	b halt

sdram_config:
	.long 0x22011110	 //BWSCON
	.long 0x00000700	 //BANKCON0
	.long 0x00000700	 //BANKCON1
	.long 0x00000700	 //BANKCON2
	.long 0x00000700	 //BANKCON3  
	.long 0x00000700	 //BANKCON4
	.long 0x00000700	 //BANKCON5
	.long 0x00018005	 //BANKCON6
	.long 0x00018005	 //BANKCON7
	.long 0x008C04F4	 // REFRESH
	.long 0x000000B1	 //BANKSIZE
	.long 0x00000030	 //MRSRB6
	.long 0x00000030	 //MRSRB7

2.2 boot.lds link script

SECTIONS {
    . = 0x33f80000;
    .text : { *(.text) }
    
    . = ALIGN(4);
    .rodata : {*(.rodata*)} 
    
    . = ALIGN(4);
    .data : { *(.data) }
    
    . = ALIGN(4);
    __bss_start = .;
    .bss : { *(.bss)  *(COMMON) }
    __bss_end = .;
}

2.3 init.c

When we relocate, we need to judge whether norflash starts or nandflash starts. We use the following method to judge.

• If norflash is started, then the 0 address is above norflash, norflash can be read like memory but cannot be written like memory.
• If it is started by nandflash, then the 0 address is above the on-chip 4k sram, and the sram can be read and written.

In addition, the operation of clearing the bss segment is also done in init.c.

Then there is the initialization and read operation of nandflash.

2.3.1 nand_init

 The timing settings of nandflash initialization mainly have three values,

• TACLS: After issuing CLE/ALE, how long to wait for the write signal to go low.
• TWRPH0: How long does nWE keep this low level.
• TWRPH1: How long will this CLE/ALE remain after nWE goes high.

2.3.2 nand_read

 Through the nandflash controller of 2440, we need to set ALE to high level before sending the address, and set CLE to high level before sending the command.

1 page has 2Kbyte and 64byte OBB (out of bank). The reason why OOB is introduced is because nandflash has a bit inversion defect. For example, when we read a certain page, most of them are right, but a certain bit may be inverted. How can we avoid bit inversion, so we are in When writing page data, in addition to writing data, ECC check code is also generated. ECC is written into OOB. When reading, the ECC in OOB should be read out, and the read data should be regenerated to check code. Then compare, if not equal, will find out which bit is reversed by some algorithm.

Note that oob does not participate in the address addressing of nandflash, so how do we access oob? We can say the 0th byte in oob, or the 2049th in this page.

When we read, we issue a read command, issue an address, and nandflash will get the entire page of data into the page register, and then we issue a read operation to read the data from the page register.

When we send an address, it contains a total of five address cycles, of which the first two indicate which page in this page, and the last three indicate which page. 

From the read operation sequence diagram above, we can see that first we have to issue 00 commands, then 5 addresses, then 30 commands, then wait for the data to be ready, and then read the data.

1. chip select
2. Issue read command 00h
3. Issue address (issued in 5 steps)
4. Issue a read command 30h
5. Judgment status
6. read data

//init.c

/* 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)

#define TXD0READY   (1<<2)


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


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 char nand_data(void)
{
	return NFDATA;
}

void nand_read(unsigned int addr, unsigned char *buf, unsigned int len)
{
	int col = addr % 2048;
	int i = 0;
		
	/* 1. 选中 */
	nand_select();

	while (i < len)
	{
		/* 2. 发出读命令00h */
		nand_cmd(0x00);

		/* 3. 发出地址(分5步发出) */
		nand_addr(addr);

		/* 4. 发出读命令30h */
		nand_cmd(0x30);

		/* 5. 判断状态 */
		nand_wait_ready();

		/* 6. 读数据 */
		for (; (col < 2048) && (i < len); col++)
		{
			buf[i] = nand_data();
			i++;
			addr++;
		}
		
		col = 0;
	}

	/* 7. 取消选中 */		
	nand_deselect();
}

#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)

/*
 * 初始化UART0
 * 115200,8N1,无流控
 */
void uart0_init(void)
{
    GPHCON  |= 0xa0;    // GPH2,GPH3用作TXD0,RXD0
    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;     // 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
}

/*
 * 发送一个字符
 */
void putc(unsigned char c)
{
    /* 等待，直到发送缓冲区中的数据已经全部发送出去 */
    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;
}

void puts(char *str)
{
	int i = 0;
	while (str[i])
	{
		putc(str[i]);
		i++;
	}
}

void puthex(unsigned int val)
{
	/* 0x1234abcd */
	int i;
	int j;
	
	puts("0x");

	for (i = 0; i < 8; i++)
	{
		j = (val >> ((7-i)*4)) & 0xf;
		if ((j >= 0) && (j <= 9))
			putc('0' + j);
		else
			putc('A' + j - 0xa);
		
	}
	
}