MC68030 Datasheet, PDF (36/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Introduction
Mnemonic
cpBcc
cpDBcc
cpGEN
Description
Branch Conditionally
Test Coprocessor Condition,
Decrement and Branch
Coprocessor General Instruction
Mnemonic
cpRESTORE
cpSAVE
cpScc
cpTRAPcc
Description
Restore Internal State of Coprocessor
Save Internal State of Coprocessor
Set Conditionally
Trap Conditionally
1.6.2 Virtual Machine
A typical use for a virtual machine system is the development of software, such as an
operating system, for a new machine also under development and not yet available for
programming use. In a virtual machine system, a governing operating system emulates the
hardware of the new machine and allows the new software to be executed and debugged
as though it were running on the new hardware. Since the new software is controlled by the
governing operating system, it is executed at a lower privilege level than the governing
operating system. Thus, any attempts by the new software to use virtual resources that are
not physically present (and should be emulated) are trapped to the governing operating
system and performed by its software.
In the MC68030 implementation of a virtual machine, the virtual application runs at the user
privilege level. The governing operating system executes at the supervisor privilege level
and any attempt by the new operating system to access supervisor resources or execute
privileged instructions causes a trap to the governing operating system.
Instruction continuation is used to support virtual I/O devices in memory-mapped input/
output systems. Control and data registers for the virtual device are simulated in the memory
map. An access to a virtual register causes a fault and the function of the register is
emulated by software.
MOTOROLA
MC68030 USER’S MANUAL
1-13