首先给出一些定义:
//2440addr.inc
INTOFFSET EQU 0x4a000014 ;Interruot request source offset
//option.inc
_ISR_STARTADDRESS EQU 0x33ffff00
//2440init.s
MACRO
$HandlerLabel HANDLER $HandleLabel
$HandlerLabel
sub sp,sp,#4 ;decrement sp(to store jump address)
stmfd sp!,{r0} ;PUSH the work register to stack(lr does t push because it return to original address)
ldr r0,=$HandleLabel ;load the address of HandleXXX to r0
ldr r0,[r0] ;load the contents(service routine start address) of HandleXXX
str r0,[sp,#4] ;store the contents(ISR) of HandleXXX to stack
ldmfd sp!,{r0,pc} ;POP the work register and pc(jump to ISR)
MEND
下面进入正题:
//2440init.s
PRESERVE8
AREA RESET,CODE,READONLY
ENTRY
EXPORT __ENTRY
__ENTRY
ResetEntry
b ResetHandler ;0x0
b HandlerUndef ;handler for Undefined mode
b HandlerSWI ;handler for SWI interrupt
b HandlerPabort ;handler for PAbort
b HandlerDabort ;handler for DAbort
b . ;reserved
b HandlerIRQ ;handler for IRQ interrupt
b HandlerFIQ ;handler for FIQ interrupt
b EnterPWDN ; Must be @0x20.
...
HandlerIRQ HANDLER HandleIRQ
...
.............
; Setup IRQ handler//建立中断表
ldr r0,=HandleIRQ ;This routine is needed
ldr r1,=IsrIRQ ;if there isn t 'subs pc,lr,#4' at 0x18, 0x1c
str r1,[r0]
................
^ _ISR_STARTADDRESS ;0x33ffff00
HandleReset # 4
HandleUndef # 4
HandleSWI # 4
HandlePabort # 4
HandleDabort # 4
HandleReserved # 4
HandleIRQ # 4
HandleFIQ # 4 ;0x33ffff1C
;IntVectorTable
;@0x33FF_FF20
HandleEINT0 # 4 ;0x33ffff20
HandleEINT1 # 4
HandleEINT2 # 4
.................................
HandleUART1 # 4 ;0x33ffff7C
.................................
uart是一个外部中断,走的是FIQ.
外部中断 --> b HandlerFIQ ;
看代码发现HandlerFIQ在init.s中进行了宏定义,展开之后得到:
//展开宏 HandlerIRQ HANDLER HandleIRQ
HandlerIRQ
sub sp,sp,#4 ;decrement sp(to store jump address)
stmfd sp!,{r0} ;PUSH the work register to stack(lr does t push because it return to original address)
ldr r0,=$HandleIRQ ;load the address of HandleXXX to r0
ldr r0,[r0] ;load the contents(service routine start address) of HandleXXX
str r0,[sp,#4] ;store the contents(ISR) of HandleXXX to stack
ldmfd sp!,{r0,pc} ;POP the work register and pc(jump to ISR)
可以看到,HandlerIRQ是一个标准的中断处理过程(正因如此使用了宏进行封装): 首先保存现场,然后跳转到HandleIRQ,从HandleIRQ回来之后恢复现场.
HandleIRQ其实是一个函数指针,它可以在程序中被我们指向某一个处理函数. 这里我们指向了IsrIRQ. 在IsrIRQ里,我们读取INTOFFSET寄存器的值,加上外部中断的起始值HandleEINT0,这样我们就获得了世纪的中断入口HandleUART1. 通过ldmfd sp!,{r8-r9,pc},我们跳转进入了HandleUART1对应的实际的中断处理函数(见后面的分析).
//2440init.s
IsrIRQ
sub sp,sp,#4 ;reserved for PC
stmfd sp!,{r8-r9}
ldr r9,=INTOFFSET
ldr r9,[r9]
ldr r8,=HandleEINT0
add r8,r8,r9,lsl #2 ;//r8=r8+(r9*4)
ldr r8,[r8]
str r8,[sp,#8]
ldmfd sp!,{r8-r9,pc}
上面说到,"通过ldmfd sp!,{r8-r9,pc},我们跳转进入了HandleUART1对应的实际的中断处理函数." 怎么跳转的呢,在代码里,我们又实现并绑定了HandleUART1的处理函数Uart1_TxRxInt:
//2440addr.h
#define pISR_UART1 (*(unsigned *)(_ISR_STARTADDRESS+0x7c))
//2440lib.c
pISR_UART1=(unsigned)Uart1_TxRxInt;
extern unsigned char UartBuf1[256];
void __irq Uart0_TxRxInt(void)//这里只处理了接收中断
{
unsigned char *pbuf = UartBuf1;
if(rSUBSRCPND & BIT_SUB_RXD0) //接收中断
{
rINTSUBMSK |= BIT_SUB_RXD0;
while((rUFSTAT0&0x3f))
{
*pbuf++ = rURXH0;
}
*pbuf = '\0';
rINTSUBMSK &= ~BIT_SUB_RXD0;
rSRCPND |= BIT_UART0;
rINTPND |= BIT_UART0;
rINTSUBMSK &= ~(BIT_SUB_TXD0);
}
}
