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Cycle Timings and Interlock Behavior

16.6ARMv6 Sum of Absolute Differences (SAD)

Table 16-8 lists ARMv6 SAD instructions and gives their cycle timing behavior.

Table 16-8 ARMv6 sum of absolute differences instruction timing behavior

Instructions

Cycle

Early Reg

Result Latency

s

 

 

 

 

 

 

 

USAD8

1

<Rm>, <Rs>

3a

USADA8

1

<Rm>, <Rs>

3

a. Result latency is one less If the destination is the accumulate for a subsequent USADA8.

16.6.1Example interlocks

Table 16-9 lists interlock examples using USAD8 and USAD8 instructions.

 

 

Table 16-9 Example interlocks

 

 

Instruction sequence

Behavior

 

 

 

USAD8

R1,R2,R3

Takes four cycles because USAD8 has a Result Latency of three, and the ADD requires the

ADD

R5,R6,R1

result of the USAD8 instruction.

 

 

 

USAD8

R1,R2,R3

Takes four cycles. The MOV instructions are scheduled during the Result Latency of the

MOV

R9,R9

USAD8 instruction.

MOV

R9,R9

 

ADD

R5,R6,R1

 

 

 

 

USAD8

R1,R2,R3

Takes three cycles. The Result Latency is one less because the result is used as the accumulate

USADA8 R1,R4,R5,R1

for a subsequent USADA8 instruction.

 

 

 

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