Question

Please explain in detail..... for an easy understanding

1. Describe the following types of data hazards. RAW WAR WAW 2. Give a short ARM example for each hazard. 3. Explain some techniques for handling these types of hazards.

Answer 1

Hazards are the problems associated with the CPU, there are different type of hazards depending on the operation by which it is caused...

1. RAW (Read After Write) :-
When instruction 2 tries to read the source before instruction 1 writes to it. This can occur because even though an instruction is executed after a prevoius instruction, the previous instruction has not been completely processed through the pipeline.

ex.

1. R2 <- R1 + R3
2. R4 <- R2 + R3

Here the first instruction is calculating a value to be saved in register R2 and second is going to use this value to compute a result for R4.

2. WAR (Write after Read) :-
In this type of hazard the instruction 2 tries to write destination before it is read by instruction 1.

ex.

1. R4 <- R1 + R5
2. R5 <- R1 + R2

Here concurrent execution may cause this hazard.

3. WAW (Write After Write) :-
In this type of hazad instruction 2 tries to write the source before the instruction 1 writes the result to the source.

ex.

1. R2 <- R4 + R7
2. R2 <- R1 + R3