redboot启动代码疑惑，各位大侠帮忙看看。

junior1108 2009-05-28 04:31:40

小弟今天刚开始看redboot启动代码，发现一个问题请各位大侠指教？就是这条语句UNMAPPED_PTR(reset_vector)的目的何在？为啥不可以写成PTR(reset_vector)呢?
先谢过各位！！！！！

#define PTR(name) \
.##name: .word name

#ifndef UNMAPPED
#ifdef CYGHWR_HAL_ARM_HAS_MMU
# ifndef CYGHWR_HAL_ROM_VADDR
# define CYGHWR_HAL_ROM_VADDR __exception_handlers
# endif
# define UNMAPPED(x) ((x)-CYGHWR_HAL_ROM_VADDR)
#else
# define UNMAPPED(x) (x)
#endif
#endif

#define UNMAPPED_PTR(name) \
.##name: .word UNMAPPED(name)
.global __exception_handlers
__exception_handlers:
#ifdef CYGSEM_HAL_ROM_RESET_USES_JUMP
// Assumption: ROM code has these vectors at the hardware reset address.
// A simple jump removes any address-space dependencies [i.e. safer]
b reset_vector // 0x00
#else
ldr pc,.reset_vector // 0x00
#endif
ldr pc,.undefined_instruction // 0x04
ldr pc,.software_interrupt // 0x08 start && software int
ldr pc,.abort_prefetch // 0x0C
ldr pc,.abort_data // 0x10
.word 0 // unused
ldr pc,.IRQ // 0x18
ldr pc,.FIQ // 0x1C
.global vectors
vectors:
UNMAPPED_PTR(reset_vector) // 0x20
PTR(undefined_instruction) // 0x24
PTR(software_interrupt) // 0x28
PTR(abort_prefetch) // 0x2C
PTR(abort_data) // 0x30
.word 0 // 0x34
PTR(IRQ) // 0x38
PTR(FIQ) // 0x3c
#ifdef CYGSEM_HAL_ARM_PID_ANGEL_BOOT
PTR(start) // This is copied to 0x28 for bootup // 0x40
#endif

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