请教有关中断安装

xfzhang9

在AT91_init.c中有如下中断安装函数，有如下不解之处请指教
void install_irqhandler(void * isr)
{
        /* ARM irq exception vector addr is 0x00000018  */
        unsigned int * irq_vec_addr = ( unsigned int * ) 0x18;
        /* this is isr entry address, could be another address like 0x3c, 0x58... */
        unsigned int * isr_entry_addr = ( unsigned int * ) 0x38;

        unsigned int instruction;
       
        /* set the ISR entry at 0x38  */
        *isr_entry_addr = (unsigned int)isr;
       
        /* make an instruction: it is machine-code for "ldr  pc, [pc, #(38-18-]"  */
        instruction = ((unsigned int) isr_entry_addr  - (unsigned int)irq_vec_addr - 0x0 | 0xe59ff000;
       
        /* set this instruction at 0x18  */
        *irq_vec_addr = instruction;       
}
上面程序中 instruction = ((unsigned int) isr_entry_addr  - (unsigned int)irq_vec_addr - 0x0 | 0xe59ff000;//看不懂是什么用意，谁能够解释一下多谢！！

chyyuu

instruction的内容是一个指令，即，ldr pc, [pc, #(38-18-]
然后把这条指令放到irq_vec_addr地址处。
这样但产生中断后，会执行此处的指令，这样可以把pc指向真正的中断处理程序入口。

xfzhang9

明白了