是在 BF51×_HardWare 的规格书里提到过：第26章节：SYSTEM RESET AND BOOTING（1247页）提到过：
There is a subroutine in the boot kernel known as "preboot", which is executed
prior to the boot mode being processed. This preboot routine can
customize default values of MMR registers, such as the PLL and SDRAM
controller registers. Furthermore, the SPI master mode can be customized.
The preboot behavior is controlled through OTP programming.
To enable booting from volatile memories such as SDRAM, the SDRAM
controller must be programmed before data can be loaded into the memory.
Either the preboot or the initialization code mechanism can be used
for this purpose.
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2012/3/18 22:51:37
