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Cycle Timings and Interlock Behavior

16.2Register interlock examples

Table 16-3 lists register interlock examples using LDR and ADD instructions.

LDR instructions take one cycle, have a result latency of three, and require their base register as an Early Reg.

ADD instructions take one cycle and have a result latency of one.

 

Table 16-3 Register interlock examples

 

 

Instruction sequence

Behavior

 

 

LDR R1, [R2]

Takes two cycles because there are no register dependencies

ADD R6, R5, R4

 

 

 

ADD R1, R2, R3

Takes two cycles because ADD instructions have a result latency of one

ADD R9, R6, R1

 

 

 

LDR R1, [R2]

Takes four cycles because of the result latency of R1

ADD R6, R5, R1

 

 

 

ADD R1, R5, R6

Takes three cycles because of the use of the result of R1 as an Early Reg

LDR R2, [R1]

 

 

 

LDR R1, [R2]

Takes five cycles because of the result latency and the use of the result of R1 as an Early Reg

LDR R5, [R1]

 

 

 

ARM DDI 0333H

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