uclinux-2008r1-rc8(bf561)的中断处理(3)：trap

 

  

这部分代码用于处理Exception中断，对于内核而言是相当重要的，其实现在arch/blackfin/mach-common/entry.S文件中。

ENTRY(_trap) /* Exception: 4th entry into system event table(supervisor mode)*/

       /* Since the kernel stack can be anywhere, it's not guaranteed to be

        * covered by a CPLB. Switch to an exception stack; use RETN as a

        * scratch register (for want of a better option).

        */

       EX_SCRATCH_REG = sp;

       sp.l = _exception_stack_top;

       sp.h = _exception_stack_top;

       /* Try to deal with syscalls quickly. */

       [--sp] = ASTAT;

       [--sp] = (R7:6, P5:4);

       DEBUG_STOP_HWTRACE(p5, r7)

       r7 = SEQSTAT;             /* reason code is in bit 5:0 */

       r6.l = lo(SEQSTAT_EXCAUSE);

       r6.h = hi(SEQSTAT_EXCAUSE);

       r7 = r7 & r6;

       p5.h = _ex_table;

       p5.l = _ex_table;

       p4 = r7;

       p5 = p5 + (p4 << 2);

       p4 = [p5];

       jump (p4);

 

.Lbadsys:

       r7 = -ENOSYS;            /* signextending enough */

       [sp + PT_R0] = r7;       /* return value from system call */

       jump .Lsyscall_really_exit;

ENDPROC(_trap)

 

在这里EX_SCRATCH_REG定义成RETN这个寄存器。

而_exception_stack_top是在本文件中定义的缓冲区的最高位置。

_exception_stack:

//     .rept 1024

//     .long 0;

//     .endr

       .byte4 _exception_stack_buffer[1024];

_exception_stack_top:

_ex_table是在本文件中定义的函数指针的数组，它指明了所有可能的64种异常的入口：

ENTRY(_ex_table)

       /* entry for each EXCAUSE[5:0]

        * This table must be in sync with the table in ./kernel/traps.c

        * EXCPT instruction can provide 4 bits of EXCAUSE, allowing 16 to be user defined

        */

       .long _ex_syscall       /* 0x00 - User Defined - Linux Syscall */

       .long _ex_soft_bp       /* 0x01 - User Defined - Software breakpoint */

…

_ex_table.end:

因而，这一段程序就是根据不同的EXCEPTION的类型，调用相应的入口函数进行处理。