RX610 Group
2. CPU
R01UH0032EJ0120 Rev.1.20
Page 77 of 1006
Feb 20, 2013
2.8
Pipeline
2.8.1
Overview
The RX CPU has 5-stage pipeline structure. The RX CPU instruction is converted into one or more micro-operations,
which are then executed in pipeline processing. In the pipeline stage, the IF stage is executed in the unit of instructions,
while the D and subsequent stages are executed in the unit of micro-operations.
The operation of pipeline and respective stages is described below.
(1)
IF stage (instruction fetch stage)
In the IF stage, the CPU fetches instructions from the memory. As the RX CPU has four 8-byte instruction queues, it
fetches instructions until the instruction queue is full, regardless of the completion of decoding in the D (decoding) stage.
(2)
D stage (decoding stage)
The CPU decodes instructions in the D stage and converts them into micro-operations. The CPU reads the register
information (RF) in this stage and executes a bypass process (BYP) if the result of the preceding instruction will be used
in a subsequent instruction. The write of operation result to the register (RW) can be executed with the register reference
by using the bypass process.
(3)
E stage (execution stage)
Operations and address calculations (OP) are processed in the E stage.
(4)
M stage (memory access stage)
Operand memory accesses (OA) are processed in the M stage. This stage is used only when the memory is accessed, and
is divided into two sub-stages, M1 and M2. The RX CPU enables respective memory accesses for M1 and M2.
•
M1 stage (memory-access stage 1)
Operand memory access (OA1, OA2) is processed.
Store operation: The pipeline processing ends when a write request is received via the bus.
Load operation: The operation proceeds to the M2 stage when a read request is received via the bus. If a request and
load data are received at the same timing (no-wait memory access), the operation proceeds to the WB stage.
•
M2 stage (memory-access stage 2)
Operand memory access (OA2) is processed. The CPU waits for the load data in the M2 stage. When the load data
is received, the operation proceeds to the WB stage.
(5)
WB stage (write-back stage)
The operation result and the data read from memory are written to the register (RW) in the WB stage. The data read from
memory and the other type of data, such as the operation result, can be written to the register in the same clock cycles.
Summary of Contents for RX600 Series
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