Epson ARM720T Benutzerhandbuch

The ARM720T core and any coprocessors in the system perform a handshake using the signals 

shown in Table 8-2.

These signals are explained in more detail in 

The coprocessor decodes the instruction currently in the Decode stage of its pipeline and 

checks whether that instruction is a coprocessor instruction. A coprocessor instruction has a 

coprocessor number that matches the coprocessor ID of the coprocessor.
If the instruction currently in the Decode stage is a coprocessor instruction:

1

The coprocessor attempts to execute the instruction.

2

The coprocessor signals back to the ARM720T core using EXTCPA and EXTCPB.

Coprocessor instructions progress down the ARM720T processor pipeline in step with the 

coprocessor pipeline. A coprocessor instruction is executed if the following are true:

1

The coprocessor instruction has reached the Execute stage of the pipeline. (It might 

not if it was preceded by a branch.)

2

The instruction has passed its conditional execution tests.

3

A coprocessor in the system has signalled on EXTCPA and EXTCPB that it is able 

to accept the instruction.

If all these requirements are met, the ARM720T processor signals by taking CPnCPI LOW. 

This commits the coprocessor to the execution of the coprocessor instruction.

Table 8-2  Handshaking signals

ARM720T core to coprocessor

Not coprocessor instruction

Coprocessor to ARM720T core

Coprocessor absent

Coprocessor to ARM720T core

Coprocessor busy