80960MC datasheet(10/39 Pages) INTEL

10 / 39 page

80960MC

PRELIMINARY

Figure 3. Multiple Register Sets Are Stored On-Chip

CACHE

ONE OF FOUR

LOCAL

LOCAL REGISTER SET

R15

1.1.7

Memory Management and Protection

The 80960MC is ideal for multitasking applications

that require software protection and a large address

space. To ensure the highest level of performance

possible, the memory management unit (MMU) and

translation look-aside buffer (TLB) are contained on-

chip.

The 80960MC supports a conventional form of

demand-paged virtual memory in which the address

space is divided into 4-Kbyte pages. Studies indicate

that a 4-Kbyte page is the optimum size for a broad

range of applications.

Each page table entry includes a 2-bit page rights

field that specifies whether the page is a no-access,

read-only, or read-write page. This field is inter-

preted differently depending on whether the current

task (process) is executing in user or supervisor

mode, as shown below:

Rights

User

Supervisor

No Access

Read-Only

No Access

Read-Write

Read-Only

Read-Write

1.1.8

Floating-Point Arithmetic

In the 80960MC, floating-point arithmetic is an

integral part of the architecture. Having the floating-

point unit integrated on-chip provides two advan-

tages. First, it improves the performance of the chip

for floating-point applications, since no additional

bus overhead is associated with floating-point calcu-

lations, thereby leaving more time for other bus oper-

ations such as I/O. Second, the cost of using

floating-point operations is reduced because a

separate coprocessor chip is not required.

The 80960MC floating-point (real-number) data

types include single-precision (32-bit), double-preci-

sion (64-bit) and extended precision (80-bit) floating-

point numbers. Any registers may be used to

execute floating-point operations.

The processor provides hardware support for both

mandatory and recommended portions of IEEE

Standard 754 for floating-point arithmetic, including

all arithmetic, exponential, logarithmic and other

transcendental functions. Table 3 shows execution

times for some representative instructions.

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