What is the difference with using NOP and kiosks in MIPS

Question

What difference does it make to use a NOP instead of a stall. Both of them perform the same task in the case of conveyor processing. I can not understand

Answer 1

I think you mixed up your terminology.

The delay is introduced into the pipeline by the processor to eliminate the dangers of the data (situations where the data necessary to process the instruction is not yet available. NOPIs just an instruction without a side effect.

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Benches

Recall stage 5 of the classic RISC pipeline conveyor :

1. IF - extract instructions (fetch the next instruction from memory)
2. ID - Decoding the instruction (find out what the instruction is and what the operands are)
3. EX - ( )
4. MEM - ( )
5. WB - ( )

:

add $t0, $t1, $t1
sub $t2, $t0, $t0

, . : (RAW); .

sub add EX, add MEM - WB:

+------------------------------+----+----+----+-----+----+---+---+---+---+
|                              |         CPU Cycles                      |
+------------------------------+----+----+----+-----+----+---+---+---+---+
|         Instruction          | 1  | 2  | 3  | 4   | 5  | 6 | 7 | 8 | 9 |
+------------------------------------------------------------------------+
|       0 | add $t0, $t1, $t1  | IF | ID | EX | MEM | WB |   |   |   |   |
|       1 | sub $t2, $t0, $t0  |    | IF | ID | EX  |    |   |   |   |   |
+---------+--------------------+----+----+----+-----+----+---+---+---+---+

, , .

+------------------------------+----+----+----+-----+----+----+-----+---+----+
|                              |         CPU Cycles                          |
+------------------------------+----+----+----+-----+----+----+-----+----+---+
|         Instruction          | 1  | 2  | 3  | 4   | 5  | 6  | 7   | 8  | 9 |
+----------------------------------------------------------------------------+
|        0 | add $t0, $t1, $t1 | IF | ID | EX | MEM | WB |    |     |    |   |
|        1 | sub $t2, $t0, $t0 |    | IF | ID | S   | S  | EX | MEM | WB |   |
+----------+-------------------+----+----+----+-----+----+---+---+---+-------+

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NOPS

NOP - , ( ). MIPS nop MIPS sll $zero $zero 0.

5 . , .

j label
nop # nothing useful to put here

MIPS, , . (, spim -delayed_branches)