redboot启动代码？各位大侠帮帮看看

只看该作者 · 2009-5-28 16:26

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

// The layout of these pointers should match the vector table above since
// they are copied in pairs.
        .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