Cache Memory; System Cache - Teknor Industrial Computers TEK-AT4LVG Technical Reference Manual

Industrial single board computer

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7.03

CACHE MEMORY

There are two separate Caches in the Host subsystem: Internal Cache and External Cache.

The Cache inside the processor (Internal Cache) is referred to as the first level Cache (also

primary Cache). The External Cache (called System Cache in this manual) comprises the

System Controller's Cache control circuitry and associated external memory array; it is

referred to as the second level Cache (also secondary Cache). The second level Cache is

unified, which means that both CPU data and instructions are stored in the Cache.

System Cache is located at U48, U49, U50, U51, U60, U61, U62 and U63 (#7) on

Diagram 7-1; it accepts 0KB, 128KB, 256KB or 512KB of standard asynchronous

SRAMs. The tag RAM is external to the System Controller and is situated at U36.

System Cache copies the most recently accessed data and places it in an area of high speed

memory called SRAM (Static RAM). Cache SRAM is positioned between System Memory

(DRAM) and the CPU. Data is transferred from System Memory to Cache and then from

Cache to the CPU.

Since most program executions are sequential and repetitive, the likelihood is great that

the CPU will find data already stored in either Cache. When the CPU retrieves data from

Cache, a Cache hit occurs. On the other hand, when the CPU must access data from

System Memory, a Cache miss occurs.

System Cache is enabled in the AWARD Setup program.

1. From AWARD's Main Menu, select the BIOS Features Setup option.

2. In the BIOS Features Setup Menu:

Select the CPU Internal Cache option, or

Select the External Cache option.

In both cases, you will have the option to choose between Disabled and Enabled

(Disabled is the default value).

Installing and Working With System Components

7-6

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