Virtual Machine - Motorola MC68030 User Manual

Mnemonic
cpBcc Branch Conditionally
cpDBcc Test Coprocessor Condition,
Decrement and Branch
cpGEN Coprocessor General Instruction

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
Description
MC68030 USER'S MANUAL
Mnemonic
cpRESTORE Restore Internal State of Coprocessor
cpSAVE Save Internal State of Coprocessor
cpScc Set Conditionally
cpTRAPcc Trap Conditionally
Introduction
Description
1-13