问 在keil环境下，使用WWW.AT91.COM的例程，发现启动文件有下述问题，
需修改两行代码：即加注释的两行代码。

IRQ_Handler_Entry

;- Manage Exception Entry
;- Adjust and save LR_irq in IRQ stack
                sub         lr, lr, #4
                stmfd       sp!, {lr}

;- Save SPSR need to be saved for nested interrupt
                mrs         r14, SPSR
                stmfd       sp!, {r14}

;- Save and r0 in IRQ stack
                stmfd       sp!, {r0}

;- Write in the IVR to support Protect Mode
;- No effect in Normal Mode
;- De-assert the NIRQ and clear the source in Protect Mode
                ldr         r14, =AT91C_BASE_AIC
                ldr         r0 , [r14, #AIC_IVR]
                str         r14, [r14, #AIC_IVR]

;- Enable Interrupt and Switch in Supervisor Mode
                msr         CPSR_c, #Mode_SVC

;- Save scratch/used registers and LR in User Stack
                stmfd       sp!, { r1-r3, r12, r14}

;- Branch to the routine pointed by the AIC_IVR
;               mov         r14, pc
                add         r14, pc, #4                 ;// 修改
                bx          r0

;- Restore scratch/used registers and LR from User Stack
                msr         CPSR_c, #Mode_SVC           ;// 增加
                ldmia       sp!, { r1-r3, r12, r14}

;- Disable Interrupt and switch back in IRQ mode
                msr         CPSR_c, #I_Bit :OR: Mode_IRQ

;- Mark the End of Interrupt on the AIC
                ldr         r14, =AT91C_BASE_AIC
                str         r14, [r14, #AIC_EOICR]

;- Restore SPSR_irq and r0 from IRQ stack
                ldmia       sp!, {r0}

;- Restore SPSR_irq and r0 from IRQ stack
                ldmia       sp!, {r14}
                msr         SPSR_cxsf, r14

;- Restore adjusted  LR_irq from IRQ stack directly in the PC
                ldmia       sp!, {pc}^

做上述修改后，可实现中断嵌套。
请版主指点，上述修改是否必要？

由于没有仿真器，调试不便，还请各位同仁多多帮忙！
谢了 答 1: 哦哦你的错了，你这就是画蛇添足，多看看书。