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Instruction Execution (命令の実行)

1.
Instruction Fetch [Fetch] (命令の読み出し) : Copy the PC into the MA register. Read from memory the value stored at the address pointed to by MA and store in MD. Copy the value in MD to the IR. Increment the PC.

2.
Instruction Decode [Decode] (命令の解読) : Decode the instruction.

3.
Operand Address Calculation [Address] (オペランド・アドレスの計算: Determine the address of the operand and store it in MA.

4.
Operand Fetch [Operand] (オペランドの読み出し) : Read the operand from the memory location pointed to by MA and store it in MD.

5.
Execution [Execution] (実行) : Execute the instruction.

6.
Write Result [Write] (結果の保存) : The result of the instruction is stored.



Example: the add instruction



Step Actions
T0 MA $\leftarrow$ PC; C $\leftarrow$ PC + 4
T1 MD $\leftarrow$ M[MA]; PC $\leftarrow$ C
T2 IR $\leftarrow$ MD
T3 A $\leftarrow$ R[ra]
T4 C $\leftarrow$ A + R[rb]
T5 R[rc] $\leftarrow$ C


next up previous contents
Next: Improving Performance (性能向上へ) Up: CPU Architecture (I) - Previous: Types of Instructions (命令の種類)
David Asano
2001-05-29