TS68020VR16 Atmel, TS68020VR16 Datasheet - Page 32

• Manufacturer Part Number: TS68020VR16
• Description: IC MPU 32BIT 16.67MHZ 114PGA
• Manufacturer: Atmel

Specifications of TS68020VR16

• Processor Type: 68000 32-Bit
• Speed: 16.67MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 114-PGA
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -

Multi-processing
Module Support
Virtual Memory/Machine
Concepts
Virtual Memory
32
TS68020
To further support multi-processing with the TS68020, a compare and swap instruction,
CAS, has been added. This instruction makes use of the read-modify-write cycle to
compare two operands and swap a third operand pending the results of the compare. A
variant of this instruction, CAS2, performs similarly comparing dual operand pairs, and
updating two operands.
These multi-processing operations are useful when using common memory to share or
pass data between multiple processing elements. The read-modify-write cycle is an indi-
visible operand that allows reading and updating a “lock” operand used to control
access to the common memory elements. The CAS2 instruction is more powerful since
dual operands allow the “lock” to the checked and two values (i.e., both pointers in a
doubly-linked list) to be updated according to the lock’s status, all in a single operation.
The TS68020 includes support for modules with the call module (CALLM) and return
from module (RTM) instructions. The CALLM instruction references a module descrip-
tor. This descriptor contains control information for entry into the associated module.
The CALLM instruction creates a module stack frame and stores the module state in
that frame. The RTM instruction recovers the previous module state from the stack
frame and returns to the calling module.
The module interface also provides a mechanism for finer resolution of access control
by external hardware. Although the TS68020 does not interrupt the access control infor-
mation, it does communicate with external hardware when the access control is to be
changed, and relies on the external hardware to verify that the changes are legal.
CALLM and RTM, when used as subroutine calls and returns with proper descriptor for-
mats, cause the TS68020 to perform the necessary actions to verify legitimate access to
modules.
The full addressing range of the TS68020 is 4-Gbyte (4, 294, 967, 296). However, most
TS68020 systems implement a smaller physical memory. Nonetheless, by using virtual
memory techniques, the system can be made to appear to have a full 4-Gbyte of physi-
cal memory available to each user program. These techniques have been used for
many years in large mainframe computers and minicomputers. With the TS68020 (as
with the TS68010 and TS68012), virtual memory can be fully supported in microproces-
sor-based systems.
In a virtual memory system, a user program can be written as though it has a large
amount of memory available to it when actually only a smaller amount of memory is
physically present in the system. In a similar fashion, a system provides user programs
access to other devices that are not physically present in the system, such as tape
drives, disk drives, printers, or terminals. With proper software emulation, a physical
system can be made to appear to a user program as any other 68000 computer system
and the program may be given full access to all of the resources of that emulated sys-
tem. Such an emulator system is called a virtual machine.
The basic mechanism for supporting virtual memory is to provides a limited amount of
high-speed physical memory that can be accessed directly by the processor while main-
taining of a much larger “virtual” memory on secondary storage devices such as large
capacity disk drives. When the processor attempts to access a location in the virtual
memory map that is not resident in the physical memory (referred to as a page fault), the
access to that location is temporarily suspended while the necessary data is fetched
from secondary storage and placed in physical memory; the suspended access is then
either restarted or continued.
2115A–HIREL–07/02