Fromlasttime.PDF

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Fromlasttime.PDF

From last time Explain the differences between LDR instructions LDM instructions. (4 marks) LDR loads 1 value from memory into a register. LDM can load several values into registers from adjacent memory locations. Explain the effect of the following ARM instruction on the registers involved and on memory: (2 marks) STMFD SP!, {R0, R3-R5} SP is decreased by 16 (4 words of 4 bytes). Copies of registers R0, R3, R4, R5 are stored in memory locations [SP], [SP+4], [SP+8], [SP+12] From last time ctd. A method is passed two integer arguments via the stack, which it adds together, and returns the result in R0. The method also puts the Link Register on the stack (e.g. because it also calls “println” – but don’t include the code for this call in your answer). Give the ARM code required for a simple implementation of the method and draw a diagram of the resulting stack frame. (4 marks) PUSH {R1,LR} LDR R0, [SP,#8] R1 SP LDR R1, [SP,#12] LR SP+4 ADD R0, R0, R1 param1 SP+8 LDR R1, [SP],#4 param2 SP+12 LDR PC, [SP],#12 Question: ARM code for if-else version? Note: System.out.print(2); becomes: MOV R0, #’2’ then SVC 0 LDR R0, number tryfour CMP R0, #0 CMP R0, #4 BNE trytwo BNE default MOV R0, #’0’ MOV R0, #’4’ SVC 0 SVC 0 B end B end trytwo default

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