chapter 9 trap routines and subroutines
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Chapter 9 TRAP Routines and Subroutines. System Calls. System Call. LC-3 TRAP Mechanism. TRAP Instruction. TRAP. RET (JMP R7). TRAP Mechanism Operation. TRAP Routines and their Assembler Names. Example: Using the TRAP Instruction. Example: Output Service Routine. TRAP_PUTS - PowerPoint PPT Presentation
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Chapter 9TRAP Routines and
Subroutines
System Calls
System Call
LC-3 TRAP Mechanism
TRAP Instruction
TRAP
RET (JMP R7)
TRAP Mechanism Operation
TRAP Routines and their Assembler Names
Example: Using the TRAP Instruction
9-12
Example: Output Service RoutineTRAP_PUTS
ST R0,OS_SAVE_R0 ; save R0, R1, and R7ST R1,OS_SAVE_R1ST R7,OS_SAVE_R7ADD R1,R0,#0 ; move string pointer (R0) into R1
TRAP_PUTS_LOOPLDR R0,R1,#0 ; write characters in string using OUTBRz TRAP_PUTS_DONEOUTADD R1,R1,#1BRnzp TRAP_PUTS_LOOP
TRAP_PUTS_DONELD R0,OS_SAVE_R0 ; restore R0, R1, and R7LD R1,OS_SAVE_R1LD R7,OS_SAVE_R7RET
stored in table,location x22
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