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AREA TopSwiHandler, CODE ; name this block of code
EXPORT SWIHandler
EXPORT MakeChain
IMPORT C_SWI_Handler
IMPORT Dswivec
SWIHandler
SUB r13, r13, #4 ; leave space to store spsr
STMFD r13!, {r0-r12,r14} ; store registers
MOV r1, r13 ; second parameter to C routine
; is register values.
LDR r0,[r14,#-4] ; Calculate address of SWI instruction
; and load it into r0
BIC r0,r0,#0xff000000 ; mask off top 8 bits of instruction
MRS r2, spsr
STR r2,[r13,#14*4] ; store spsr on stack at original r13
BL C_SWI_Handler ; Call C routine to handle SWI
CMP r0, #0 ; Has C routine handled SWI ?
; 0 = no, 1 = yes
LDR r2, [r13,#14*4] ; extract spsr from stack
MSR spsr,r2 ; and restore it
LDMFD r13!, {r0-r12,lr} ; Restore original registers
ADD r13,r13,#4
; Now need to decide whether to return from handler or to call
; the next handler in the chain (the debugger's).
MOVNES pc,lr ; return from handler if SWI handled
LDR pc, swichain ; else jump to address containing
; instruction to branch to address of
; debugger's SWI handler.
swichain
DCD 0
MakeChain
LDR r0, =swichain
LDR r1, =Dswivec
LDR r2, [r1]
STR r2, [r0]
MOV pc,lr
END ; mark end of this file
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