Flash erase/program 检查方法

  注意:读本篇文章要对flash的操作有些基础知识，或者要找份datasheet来看看。
 
  有两种方法Data polling 和Toggle bit

1. Data Polling
   在erase/programcmd写下去之后，Q7位会变成data取反(因为erase后是0xff，所以这时Q7=0),然后直到erase/program操作结束，Q7才会变成实际的data。也就是flash进入普通的read模式。所以我们在写driver时，是可以使用 erase:while(*addr==0xff); program: while(*addr==data); 这样的方法来等待操作结束的。
2. Toggle Bit
   在erase/program cmd写下去之后, Q6位在连续的两次读操作中，读出的数据会相反，直到erase/program操作结束.参考这样一段代码

int FlashDataToggle( void )
{
   volatile FLASH_DEF u1, u2; /* hold values read from any address offset within
                           the Flash Memory */
   volatile FLASH_DEF * pFA;

   while( 1 ) /* TimeOut!: If, for some reason, the hardware fails then this
                  loop may not exit. Use a timer function to implement a timeout
                  from the loop. */
   {
      /* Step 1: Read DQ6 (into a word) */
      pFA = FLASH_CAST(FLASH_ADRS); /* Read DQ6 from the Flash (any address) */
      u1 = *pFA;
      /* Step 2: Read DQ5 and DQ6 (into another word) */
      u2 = *pFA; //FlashRead( ANY_ADDR ); /* Read DQ5 and DQ6 from the Flash (any


      /* Step 3: If DQ6 did not toggle between the two reads then return
                 FLASH_SUCCESS */
      if( (u1&0x40) == (u2&0x40) ) /* DQ6 == NO Toggle */
         return FLASH_SUCCESS;

      /* Step 4: Else if DQ5 is zero then operation is not yet complete */
      if( (u2&0x20) == 0x00 )
         continue;

      /* Step 5: Else (DQ5 == 1), read DQ6 again */
      u1 = *pFA; //FlashRead( ANY_ADDR ); /* Read DQ6 from the Flash (any address) */

      u2 = *pFA; //FlashRead( ANY_ADDR ); /* Read DQ6 from the Flash (any address) */

      /* Step 6: If DQ6 did not toggle between the last two reads then
                 return FLASH_SUCCESS */
      if( (u2&0x40) == (u1&0x40) ) /* DQ6 == NO Toggle */
         return FLASH_SUCCESS;

      /* Step 7: Else return FLASH_TOGGLE_FAIL */
      else { /* DQ6 == Toggle here means fail */
         return FLASH_TOGGLE_FAIL;
      }
   } /* end of while loop */
}