C167CS-4RM datasheet(56/517 Pages) INFINEON

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C167CS

Derivatives

The Central Processing Unit (CPU)

User’s Manual

4-6

V2.0, 2000-07

4.2

Particular Pipeline Effects

Since up to four different instructions are processed simultaneously, additional hardware

has been spent in the C167CS to consider all causal dependencies which may exist on

instructions in different pipeline stages without a loss of performance. This extra

hardware (i.e. for ‘forwarding’ operand read and write values) resolves most of the

possible conflicts (e.g. multiple usage of buses) in a time optimized way and thus avoids

that the pipeline becomes noticeable for the user in most cases. However, there are

some very rare cases, where the circumstance that the C167CS is a pipelined machine

requires attention by the programmer. In these cases the delays caused by pipeline

conflicts can be used for other instructions in order to optimize performance.

Context Pointer Updating

An instruction, which calculates a physical GPR operand address via the CP register, is

mostly not capable of using a new CP value, which is to be updated by an immediately

preceding instruction. Thus, to make sure that the new CP value is used, at least one

instruction must be inserted between a CP-changing and a subsequent GPR-using

instruction, as shown in the following example:

:SCXT CP,#0FC00h ;select a new context

In + 1: …

;must not be an instruction using a GPR

In + 2:MOV R0,#dataX

;write to GPR 0 in the new context

Data Page Pointer Updating

An instruction, which calculates a physical operand address via a particular DPPn

(n = 0 to 3) register, is mostly not capable of using a new DPPn register value, which is

to be updated by an immediately preceding instruction. Thus, to make sure that the new

DPPn register value is used, at least one instruction must be inserted between a DPPn-

changing instruction and a subsequent instruction which implicitly uses DPPn via a long

or indirect addressing mode, as shown in the following example:

:MOV DPP0,#4

;select data page 4 via DPP0

In + 1:…

;must not be an instruction using DPP0

In + 2:MOV DPP0:0000H,R1;move contents of R1 to address location

;01’0000H (in data page 4) supposed segment.

;is enabled

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