Linux之uboot入门(四)---start.s分析
上一篇分析makefile,到uboot的启动代码。
也称之为第一阶段。在lds链接脚本中指向cpu/arm920t/start.s&boot_init.s文件。
那么我们今天从start.s文件开始分析。
首先是硬件相关设定：
1、设置CPU工作模式为svc32
（这里为什么要设置为SVC32 mode，请参考https://blog.csdn.net/shao15232/article/details/106246517）
reset: /* 设置CPU工作模式为SVC32 */
/*
* set the cpu to SVC32 mode
*/
mrs r0,cpsr
bic r0,r0,#0x1f
orr r0,r0,#0xd3
msr cpsr,r02、关看门狗
# define pWTCON 0x53000000
# define INTMOD 0X4A000004
# define INTMSK 0x4A000008 /* Interupt-Controller base addresses */
# define INTSUBMSK 0x4A00001C
# define CLKDIVN 0x4C000014 /* clock divisor register */
ldr r0, =pWTCON /*2410和2440关看门狗设置是一样的*/
mov r1, #0x0
str r1, [r0]
/*
* mask all IRQs by setting all bits in the INTMR - default
*/
mov r1, #0xffffffff
ldr r0, =INTMSK
str r1, [r0]
ldr r1, =0x3ff
ldr r0, =INTSUBMSK
str r1, [r0]3、设置CPU时钟 MPLL UPLL CLK_DIV
#define S3C2440_MPLL_400MHZ ((0x5c<<12)|(0x01<<4)|(0x01))
#define S3C2440_UPLL_48MHZ ((0x38<<12)|(0x02<<4)|(0x02))
#define S3C2440_CLKDIV (0x05) // | (1<<3)) /* FCLK:HCLK:PCLK = 1:4:8, UCLK = UPLL/2 */
ldr r1, =CLKDIVN
mov r2, #S3C2440_CLKDIV
str r2, [r1]
mrc p15, 0, r1, c1, c0, 0 // read ctrl register
orr r1, r1, #0xc0000000 // Asynchronous
mcr p15, 0, r1, c1, c0, 0 // write ctrl register
ldr r0,=LOCKTIME
ldr r1,=0xffffff
str r1,[r0]
// delay
mov r0, #0x200
1: subs r0, r0, #1
bne 1b
// Configure MPLL
ldr r0,=MPLLCON
ldr r1,=S3C2440_MPLL_400MHZ
str r1,[r0]
// delay
mov r0, #0x200
1: subs r0, r0, #1
bne 1b
//Configure UPLL
ldr r0, =UPLLCON
ldr r1, =S3C2440_UPLL_48MHZ
str r1, [r0]
// delay
mov r0, #0x200
1: subs r0, r0, #1
bne 1b4、根据GSTATUS[2] 来判断当前CPU应该被唤醒还是sleep
/* according to GSTATUS2[1],judgement sleep or wakeup*/
ldr r0, =GSTATUS2
ldr r1, [r0]
tst r1, #(1<<1) /* r1 & (1<<1) */
bne wake_up 5、设置栈
#define CFG_MALLOC_LEN (CFG_ENV_SIZE + 128*1024)
#define CFG_GBL_DATA_SIZE 128 /* size in bytes reserved for initial data */
stack_setup:
ldr r0, _TEXT_BASE /* upper 128 KiB: relocated uboot */
sub r0, r0, #CFG_MALLOC_LEN /* malloc area */
sub r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo */
6、relocate uboot 代码到RAM(这里可以是SDRAM也可以是SRAM芯片内置的4K RAM)
relocate: /* relocate U-Boot to RAM */
adr r0, _start /* r0 <- current position of code */
ldr r1, _TEXT_BASE /* test if we run from flash or RAM */
cmp r0, r1 /* don't reloc during debug */
beq clear_bss
ldr r2, _armboot_start
ldr r3, _bss_start
sub r2, r3, r2 /* r2 <- size of armboot */
bl CopyCode2Ram /* r0: source, r1: dest, r2: size */CopyCode2Ram需要看下面的代码：
/*主要是对NAND Flash的操作*/
#include
#include
#define BUSY 1
#define NAND_SECTOR_SIZE 512
#define NAND_BLOCK_MASK (NAND_SECTOR_SIZE - 1)
#define NAND_SECTOR_SIZE_LP 2048
#define NAND_BLOCK_MASK_LP (NAND_SECTOR_SIZE_LP - 1)
/* 供外部调用的函数 */
void nand_init_ll(void);
void nand_read_ll(unsigned char *buf, unsigned long start_addr, int size);
/* NAND Flash操作的总入口, 它们将调用S3C2410或S3C2440的相应函数 */
static void nand_reset(void);
static void wait_idle(void);
static void nand_select_chip(void);
static void nand_deselect_chip(void);
static void write_cmd(int cmd);
static void write_addr(unsigned int addr);
static unsigned char read_data(void);
/* S3C2410的NAND Flash处理函数 */
static void s3c2410_nand_reset(void);
static void s3c2410_wait_idle(void);
static void s3c2410_nand_select_chip(void);
static void s3c2410_nand_deselect_chip(void);
static void s3c2410_write_cmd(int cmd);
static void s3c2410_write_addr(unsigned int addr);
static unsigned char s3c2410_read_data(void);
/* S3C2440的NAND Flash处理函数 */
static void s3c2440_nand_reset(void);
static void s3c2440_wait_idle(void);
static void s3c2440_nand_select_chip(void);
static void s3c2440_nand_deselect_chip(void);
static void s3c2440_write_cmd(int cmd);
static void s3c2440_write_addr(unsigned int addr);
static unsigned char s3c2440_read_data(void);
/* S3C2410的NAND Flash操作函数 */
/* 复位 */
static void s3c2410_nand_reset(void)
{
s3c2410_nand_select_chip();
s3c2410_write_cmd(0xff); // 复位命令
s3c2410_wait_idle();
s3c2410_nand_deselect_chip();
}
/* 等待NAND Flash就绪 */
static void s3c2410_wait_idle(void)
{
int i;
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2410nand->NFSTAT;
while(!(*p & BUSY))
for(i=0; i<10; i++);
}
/* 发出片选信号 */
static void s3c2410_nand_select_chip(void)
{
int i;
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
s3c2410nand->NFCONF &= ~(1<<11);
for(i=0; i<10; i++);
}
/* 取消片选信号 */
static void s3c2410_nand_deselect_chip(void)
{
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
s3c2410nand->NFCONF |= (1<<11);
}
/* 发出命令 */
static void s3c2410_write_cmd(int cmd)
{
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2410nand->NFCMD;
*p = cmd;
}
/* 发出地址 */
static void s3c2410_write_addr(unsigned int addr)
{
int i;
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2410nand->NFADDR;
*p = addr & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 9) & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 17) & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 25) & 0xff;
for(i=0; i<10; i++);
}
/* 读取数据 */
static unsigned char s3c2410_read_data(void)
{
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2410nand->NFDATA;
return *p;
}
/* S3C2440的NAND Flash操作函数 */
/* 复位 */
static void s3c2440_nand_reset(void)
{
s3c2440_nand_select_chip();
s3c2440_write_cmd(0xff); // 复位命令
s3c2440_wait_idle();
s3c2440_nand_deselect_chip();
}
/* 等待NAND Flash就绪 */
static void s3c2440_wait_idle(void)
{
int i;
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2440nand->NFSTAT;
while(!(*p & BUSY))
for(i=0; i<10; i++);
}
/* 发出片选信号 */
static void s3c2440_nand_select_chip(void)
{
int i;
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
s3c2440nand->NFCONT &= ~(1<<1);
for(i=0; i<10; i++);
}
/* 取消片选信号 */
static void s3c2440_nand_deselect_chip(void)
{
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
s3c2440nand->NFCONT |= (1<<1);
}
/* 发出命令 */
static void s3c2440_write_cmd(int cmd)
{
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2440nand->NFCMD;
*p = cmd;
}
/* 发出地址 */
static void s3c2440_write_addr(unsigned int addr)
{
int i;
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2440nand->NFADDR;
*p = addr & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 9) & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 17) & 0xff;
for(i=0; i<10; i++);
*p = (addr >> 25) & 0xff;
for(i=0; i<10; i++);
}
/* 发出地址 */
static void s3c2440_write_addr_lp(unsigned int addr)
{
int i;
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2440nand->NFADDR;
int col, page;
col = addr & NAND_BLOCK_MASK_LP;
page = addr / NAND_SECTOR_SIZE_LP;
*p = col & 0xff; /* Column Address A0~A7 */
for(i=0; i<10; i++);
*p = (col >> 8) & 0x0f; /* Column Address A8~A11 */
for(i=0; i<10; i++);
*p = page & 0xff; /* Row Address A12~A19 */
for(i=0; i<10; i++);
*p = (page >> 8) & 0xff; /* Row Address A20~A27 */
for(i=0; i<10; i++);
*p = (page >> 16) & 0x03; /* Row Address A28~A29 */
for(i=0; i<10; i++);
}
/* 读取数据 */
static unsigned char s3c2440_read_data(void)
{
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
volatile unsigned char *p = (volatile unsigned char *)&s3c2440nand->NFDATA;
return *p;
}
/* 在第一次使用NAND Flash前，复位一下NAND Flash */
static void nand_reset(void)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_nand_reset();
}
else
{
s3c2440_nand_reset();
}
}
static void wait_idle(void)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_wait_idle();
}
else
{
s3c2440_wait_idle();
}
}
static void nand_select_chip(void)
{
int i;
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_nand_select_chip();
}
else
{
s3c2440_nand_select_chip();
}
for(i=0; i<10; i++);
}
static void nand_deselect_chip(void)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_nand_deselect_chip();
}
else
{
s3c2440_nand_deselect_chip();
}
}
static void write_cmd(int cmd)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_write_cmd(cmd);
}
else
{
s3c2440_write_cmd(cmd);
}
}
static void write_addr(unsigned int addr)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_write_addr(addr);
}
else
{
s3c2440_write_addr(addr);
}
}
static void write_addr_lp(unsigned int addr)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
s3c2410_write_addr(addr);
}
else
{
s3c2440_write_addr_lp(addr);
}
}
static unsigned char read_data(void)
{
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
return s3c2410_read_data();
}
else
{
return s3c2440_read_data();
}
}
/* 初始化NAND Flash */
void nand_init_ll(void)
{
S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;
#define TACLS 0
#define TWRPH0 3
#define TWRPH1 0
/* 判断是S3C2410还是S3C2440 */
if (isS3C2410)
{
/* 使能NAND Flash控制器, 初始化ECC, 禁止片选, 设置时序 */
s3c2410nand->NFCONF = (1<<15)|(1<<12)|(1<<11)|(TACLS<<8)|(TWRPH0<<4)|(TWRPH1<<0);
}
else
{
/* 设置时序 */
s3c2440nand->NFCONF = (TACLS<<12)|(TWRPH0<<8)|(TWRPH1<<4);
/* 使能NAND Flash控制器, 初始化ECC, 禁止片选 */
s3c2440nand->NFCONT = (1<<4)|(1<<1)|(1<<0);
}
/* 复位NAND Flash */
nand_reset();
}
/* 读函数 */
void nand_read_ll(unsigned char *buf, unsigned long start_addr, int size)
{
int i, j;
if ((start_addr & NAND_BLOCK_MASK) || (size & NAND_BLOCK_MASK)) {
return ; /* 地址或长度不对齐 */
}
/* 选中芯片 */
nand_select_chip();
for(i=start_addr; i < (start_addr + size);) {
/* 发出READ0命令 */
write_cmd(0);
/* Write Address */
write_addr(i);
wait_idle();
for(j=0; j < NAND_SECTOR_SIZE; j++, i++) {
*buf = read_data();
buf++;
}
}
/* 取消片选信号 */
nand_deselect_chip();
return ;
}
/* 读函数
* Large Page
*/
void nand_read_ll_lp(unsigned char *buf, unsigned long start_addr, int size)
{
int i, j;
if ((start_addr & NAND_BLOCK_MASK_LP) || (size & NAND_BLOCK_MASK_LP)) {
return ; /* 地址或长度不对齐 */
}
/* 选中芯片 */
nand_select_chip();
for(i=start_addr; i < (start_addr + size);) {
/* 发出READ0命令 */
write_cmd(0);
/* Write Address */
write_addr_lp(i);
write_cmd(0x30);
wait_idle();
for(j=0; j < NAND_SECTOR_SIZE_LP; j++, i++) {
*buf = read_data();
buf++;
}
}
/* 取消片选信号 */
nand_deselect_chip();
return ;
}
int bBootFrmNORFlash(void)
{
volatile unsigned int *pdw = (volatile unsigned int *)0;
unsigned int dwVal;
/*
* 无论是从NOR Flash还是从NAND Flash启动，
* 地址0处为指令"b Reset", 机器码为0xEA00000B，
* 对于从NAND Flash启动的情况，其开始4KB的代码会复制到CPU内部4K内存中，
* 对于从NOR Flash启动的情况，NOR Flash的开始地址即为0。
* 对于NOR Flash，必须通过一定的命令序列才能写数据，
* 所以可以根据这点差别来分辨是从NAND Flash还是NOR Flash启动:
* 向地址0写入一个数据，然后读出来，如果没有改变的话就是NOR Flash
*/
dwVal = *pdw;
*pdw = 0x12345678;
if (*pdw != 0x12345678)
{
return 1;
}
else
{
*pdw = dwVal;
return 0;
}
}
int CopyCode2Ram(unsigned long start_addr, unsigned char *buf, int size)
{
unsigned int *pdwDest;
unsigned int *pdwSrc;
int i;
if (bBootFrmNORFlash())
{
pdwDest = (unsigned int *)buf;
pdwSrc = (unsigned int *)start_addr;
/* 从 NOR Flash启动 */
for (i = 0; i < size / 4; i++)
{
pdwDest[i] = pdwSrc[i];
}
return 0;
}
else
{
/* 初始化NAND Flash */
nand_init_ll();
/* 从 NAND Flash启动 */
nand_read_ll_lp(buf, start_addr, (size + NAND_BLOCK_MASK_LP)&~(NAND_BLOCK_MASK_LP));
return 0;
}
}
static inline void delay (unsigned long loops)
{
__asm__ volatile ("1:\n"
"subs %0, %1, #1\n"
"bne 1b":"=r" (loops):"0" (loops));
}
/* S3C2440: Mpll = (2*m * Fin) / (p * 2^s), UPLL = (m * Fin) / (p * 2^s)
* m = M (the value for divider M)+ 8, p = P (the value for divider P) + 2
*/
#define S3C2440_MPLL_400MHZ ((0x5c<<12)|(0x01<<4)|(0x01))
#define S3C2440_MPLL_200MHZ ((0x5c<<12)|(0x01<<4)|(0x02))
#define S3C2440_MPLL_100MHZ ((0x5c<<12)|(0x01<<4)|(0x03))
#define S3C2440_UPLL_96MHZ ((0x38<<12)|(0x02<<4)|(0x01))
#define S3C2440_UPLL_48MHZ ((0x38<<12)|(0x02<<4)|(0x02))
#define S3C2440_CLKDIV (0x05) // | (1<<3)) /* FCLK:HCLK:PCLK = 1:4:8, UCLK = UPLL/2 */
#define S3C2440_CLKDIV188 0x04 /* FCLK:HCLK:PCLK = 1:8:8 */
#define S3C2440_CAMDIVN188 ((0<<8)|(1<<9)) /* FCLK:HCLK:PCLK = 1:8:8 */
/* Fin = 16.9344MHz */
#define S3C2440_MPLL_399MHz_Fin16MHz ((0x6e<<12)|(0x03<<4)|(0x01))
#define S3C2440_UPLL_48MHZ_Fin16MHz ((60<<12)|(4<<4)|(2))
/* S3C2410: Mpll,Upll = (m * Fin) / (p * 2^s)
* m = M (the value for divider M)+ 8, p = P (the value for divider P) + 2
*/
#define S3C2410_MPLL_200MHZ ((0x5c<<12)|(0x04<<4)|(0x00))
#define S3C2410_UPLL_48MHZ ((0x28<<12)|(0x01<<4)|(0x02))
#define S3C2410_CLKDIV 0x03 /* FCLK:HCLK:PCLK = 1:2:4 */
void clock_init(void)
{
S3C24X0_CLOCK_POWER *clk_power = (S3C24X0_CLOCK_POWER *)0x4C000000;
/* support both of S3C2410 and S3C2440, by www.100ask.net */
if (isS3C2410)
{
/* FCLK:HCLK:PCLK = 1:2:4 */
clk_power->CLKDIVN = S3C2410_CLKDIV;
/* change to asynchronous bus mod */
__asm__( "mrc p15, 0, r1, c1, c0, 0\n" /* read ctrl register */
"orr r1, r1, #0xc0000000\n" /* Asynchronous */
"mcr p15, 0, r1, c1, c0, 0\n" /* write ctrl register */
:::"r1"
);
/* to reduce PLL lock time, adjust the LOCKTIME register */
clk_power->LOCKTIME = 0xFFFFFFFF;
/* configure UPLL */
clk_power->UPLLCON = S3C2410_UPLL_48MHZ;
/* some delay between MPLL and UPLL */
delay (4000);
/* configure MPLL */
clk_power->MPLLCON = S3C2410_MPLL_200MHZ;
/* some delay between MPLL and UPLL */
delay (8000);
}
else
{
/* FCLK:HCLK:PCLK = 1:4:8 */
clk_power->CLKDIVN = S3C2440_CLKDIV;
/* change to asynchronous bus mod */
__asm__( "mrc p15, 0, r1, c1, c0, 0\n" /* read ctrl register */
"orr r1, r1, #0xc0000000\n" /* Asynchronous */
"mcr p15, 0, r1, c1, c0, 0\n" /* write ctrl register */
:::"r1"
);
/* to reduce PLL lock time, adjust the LOCKTIME register */
clk_power->LOCKTIME = 0xFFFFFFFF;
/* configure UPLL */
clk_power->UPLLCON = S3C2440_UPLL_48MHZ;
/* some delay between MPLL and UPLL */
delay (4000);
/* configure MPLL */
clk_power->MPLLCON = S3C2440_MPLL_400MHZ;
/* some delay between MPLL and UPLL */
delay (8000);
}
}
第一阶段的启动代码剩下的部分放到第七篇接着讲。