nand Flash 发出地址信号的疑惑？

#define GSTATUS1 (*(volatile unsigned int *)0x560000B0)
#define BUSY 1

typedef unsigned int S3C24X0_REG32;


/* NAND FLASH (see S3C2410 manual chapter 6) */
typedef struct {
  S3C24X0_REG32 NFCONF;
  S3C24X0_REG32 NFCMD;
  S3C24X0_REG32 NFADDR;
  S3C24X0_REG32 NFDATA;
  S3C24X0_REG32 NFSTAT;
  S3C24X0_REG32 NFECC;
} S3C2410_NAND;

/* NAND FLASH (see S3C2440 manual chapter 6, www.100ask.net) */
typedef struct {
  S3C24X0_REG32 NFCONF;
  S3C24X0_REG32 NFCONT;
  S3C24X0_REG32 NFCMD;
  S3C24X0_REG32 NFADDR;
  S3C24X0_REG32 NFDATA;
  S3C24X0_REG32 NFMECCD0;
  S3C24X0_REG32 NFMECCD1;
  S3C24X0_REG32 NFSECCD;
  S3C24X0_REG32 NFSTAT;
  S3C24X0_REG32 NFESTAT0;
  S3C24X0_REG32 NFESTAT1;
  S3C24X0_REG32 NFMECC0;
  S3C24X0_REG32 NFMECC1;
  S3C24X0_REG32 NFSECC;
  S3C24X0_REG32 NFSBLK;
  S3C24X0_REG32 NFEBLK;
} S3C2440_NAND;


typedef struct {
  void (*nand_reset)(void);
  void (*wait_idle)(void);
  void (*nand_select_chip)(void);
  void (*nand_deselect_chip)(void);
  void (*write_cmd)(int cmd);
  void (*write_addr)(unsigned int addr);
  unsigned char (*read_data)(void);
}t_nand_chip;

static S3C2410_NAND * s3c2410nand = (S3C2410_NAND *)0x4e000000;
static S3C2440_NAND * s3c2440nand = (S3C2440_NAND *)0x4e000000;

static t_nand_chip nand_chip;

/* 供外部调用的函数 */
void nand_init(void);
void nand_read(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();

/* 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;
  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;
  s3c2410nand->NFCONF &= ~(1<<11);
  for(i=0; i<10; i++);   
}

/* 取消片选信号 */
static void s3c2410_nand_deselect_chip(void)
{
  s3c2410nand->NFCONF |= (1<<11);
}

/* 发出命令 */
static void s3c2410_write_cmd(int cmd)
{
  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;
  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)
{
  volatile unsigned char *p = (volatile unsigned char *)&s3c2410nand->NFDATA;
  return *p;
}

/* 在第一次使用NAND Flash前，复位一下NAND Flash */
static void nand_reset(void)
{
  nand_chip.nand_reset();
}

static void wait_idle(void)
{
  nand_chip.wait_idle();
}

static void nand_select_chip(void)
{
  int i;
  nand_chip.nand_select_chip();
  for(i=0; i<10; i++);
}

static void nand_deselect_chip(void)
{
  nand_chip.nand_deselect_chip();
}

static void write_cmd(int cmd)
{
  nand_chip.write_cmd(cmd);
}
static void write_addr(unsigned int addr)
{
  nand_chip.write_addr(addr);
}

static unsigned char read_data(void)
{
  return nand_chip.read_data();
}


/* 初始化NAND Flash */
void nand_init(void)
{
#define TACLS 0
#define TWRPH0 3
#define TWRPH1 0

  /* 判断是S3C2410还是S3C2440 */
  if ((GSTATUS1 == 0x32410000) || (GSTATUS1 == 0x32410002))
  {
  nand_chip.nand_reset = s3c2410_nand_reset;
  nand_chip.wait_idle = s3c2410_wait_idle;
  nand_chip.nand_select_chip = s3c2410_nand_select_chip;
  nand_chip.nand_deselect_chip = s3c2410_nand_deselect_chip;
  nand_chip.write_cmd = s3c2410_write_cmd;
  nand_chip.write_addr = s3c2410_write_addr;
  nand_chip.read_data = s3c2410_read_data;

/* 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
  {
  nand_chip.nand_reset = s3c2440_nand_reset;
  nand_chip.wait_idle = s3c2440_wait_idle;
  nand_chip.nand_select_chip = s3c2440_nand_select_chip;
  nand_chip.nand_deselect_chip = s3c2440_nand_deselect_chip;
  nand_chip.write_cmd = s3c2440_write_cmd;
  nand_chip.write_addr = s3c2440_write_addr;
  nand_chip.read_data = s3c2440_read_data;

/* 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();
}


#define NAND_SECTOR_SIZE 512
#define NAND_BLOCK_MASK (NAND_SECTOR_SIZE - 1)

/* 读函数 */
void nand_read(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 ;
}

为什么写地址的时候要循环呢？ 主要是这段代码不懂：
static void s3c2410_write_addr(unsigned int addr)
{
  int i;
  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++);
}

我知道nand Flash 的地址分为A0~A7  A9~A16   A17~A24   A25  对应于 半页 block Flash的位置，但是就不知道为什么地址要右移位。第一次： *p = addr & 0xff;保留地址的低8位，第二次
*p = (addr >> 9) & 0xff; 并通过右移保存了A9~A16位，这样的话，都保存到P指向的寄存器中，那么第一次保存的低8位的地址不是被覆盖了吗？

注：本代码是韦东山的“嵌入式Linux应用开发完全手册”第8章关于nand Flash的控制操作这一章的代码

nand flash的芯片手册告诉我们，操作nand时要先传输命令，再传输地址。而地址是用4个或5个周期完成的(这得看具体芯片的手册)，每个周期传输一个地址序列。

哎，你还不了解啥就串行发送数据吧呵呵

:):):D:D解啥就串行发送数据吧呵呵