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Structural hazard A structural hazard occurs when two or more instructions t...
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Structural hazard
A structural hazard occurs when two or more instructions that are in different phases of the execution request access to the same hardware resource (memory, execution unit, etc.). In MIPS it can be easily observed when you are using the floating point division unit. The program below can be used to illustrate that situation.
v: .double 0.0 y: .double 5.0 .text l.d f3,y(r0) ;f3=y div.d f5,f3,f2 ;f5=x/y div.d f6,f2,f3 ;f6=y/x add.d f8,f5,f6 ;f8=(x/y)+(y/x) add.d f4,f3,f3 mul.d f13,f2,f4 .dataA: .word 3x: .double 10.0z: .double 0.0 main: l.d f2,x(r0) ;f2=x mul.d f7,f13,f2 mul.d f9,f4,f13 s.d f8,z(r0) s.d f9,v(r0) halt
Analyze that program and manually calculate how many clock cycles are needed to execute it on a sequential processor. Let assume that the execution of any instruction takes 5 clock cycles,the execution of div.d instruction takes additional 23 clock cycles,mul.d takes additional 6 clock cycles, add.d takes additional 3 clock cycles.
How many clock cycles are needed to execute this program on a sequential processor?