I_Bit       EQU 0x80
USR32Mode   EQU 0x10
SVC32Mode   EQU 0x13
SYS32Mode   EQU 0x1f
IRQ32Mode   EQU 0x12
FIQ32Mode   EQU 0x11

    CODE32

    AREA    IRQ,CODE,READONLY

    MACRO
$IRQ_Label HANDLER $IRQ_Exception_Function

        EXPORT  $IRQ_Label                      ; The label for exports 輸出的標號
        IMPORT  $IRQ_Exception_Function         ; The imported labels 引用的外部標號

$IRQ_Label
        SUB     LR, LR, #4                      ; Calculate the returning address 計算返回地址
        STMFD   SP!, {R0-R3, R12, LR}           ; Protects the task environments 保存任務環境
        MRS     R3, SPSR                        ; Protects the status variable 保存狀態
        STMFD   SP, {R3,LR}^                    ; Protects SPSR and SP in user status, Notice: DO NOT write back.保存SPSR和用戶狀態的SP,注意不能回寫
                                                ; If the SP is written back, it should be adjusted to its appropriate value later.如果回寫的是用戶的SP，所以后面要調整SP
        NOP
        SUB     SP, SP, #4*2

        MSR     CPSR_c, #(NoInt | SYS32Mode)    ; Switch to the System Mode 切換到系統模式 
       
        BL      $IRQ_Exception_Function         ; call the C interrupt handler funtion 調用c語言的中斷處理程序

        MSR     CPSR_c, #(NoInt | IRQ32Mode)    ; Switch bak to IRQ mode 切換回irq模式
        LDMFD   SP, {R3,LR}^                    ; Recover SPSR and SP in user status, Notic: DO NOT write back. 恢復SPSR和用戶狀態的SP,注意不能回寫
                                                ; If the SP is written back, it should be adjusted to its appropriate value later.如果回寫的是用戶的SP，所以后面要調整SP
        MSR     SPSR_cxsf, R3
        ADD     SP, SP, #4*2                    ; 

        LDMFD   SP!, {R0-R3, R12, PC}^          ;
    MEND

    END