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8: Coprocessor Interface
8-2 EPSON ARM720T CORE CPU MANUAL
The coprocessor:
1 Decodes instructions to determine whether it can accept the
instruction.
2 Indicates whether it can accept the instruction (by signaling
on EXTCPA and EXTCPB).
3 Fetches any values required from its own register bank.
4 Performs the operation required by the instruction.
If a coprocessor cannot execute an instruction, the instruction takes the undefined instruction
trap. You can choose whether to emulate coprocessor functions in software, or to design a
dedicated coprocessor.
8.1.1 Coprocessor availability
You can connect up to 16 coprocessors into a system, each with a unique coprocessor ID
number.
Some coprocessor numbers are reserved. For example, you cannot assign external
coprocessors to coprocessor numbers 14 and 15, because these are internal to the ARM720T
processor:
• CP14 is the communications channel coprocessor
• CP15 is the system control coprocessor for cache and MMU functions.
Coprocessor availability is shown in Table 8-1.
Note: If you intend to design a coprocessor, send an E-mail with coprocessor in the subject
line to info@arm.com for up to date information on coprocessor numbers that have
already been allocated.
Table 8-1 Coprocessor availability
Coprocessor
number
Allocation
15 System control
14 Debug controller
13:8 Reserved
7:4 Available to users
3:0 Reserved