A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are to cached memory locations, the average latency of memory accesses will be closer to the cache latency than to the latency of main memory.
The diagram to the right shows two memories. Each location in each memory has a datum (a cache line), which in different designs ranges in size from 8 to 512 bytes. The size of the cache line is usually larger than the size of the usual access requested by a CPU instruction, which ranges from 1 to 16 bytes. Each location in each memory also has an index, which is a unique number used to refer to that location. The index for a location in main memory is called an address. Each location in the cache has a tag, which contains the index of the datum in main memory which has been cached. In a CPU's data cache, these entries are called cache lines or cache blocks.
When the processor wishes to read or write a location in main memory, it first checks whether that memory location is in the cache. This is accomplished by comparing the address of the memory location to all tags in the cache that might contain that address. If the processor finds that the memory location is in the cache, we say that a cache hit has occurred, otherwise we speak of a cache miss. In the case of a cache hit, the processor immediately reads or writes the data in the cache line. The proportion of accesses that result in a cache hit is known as the hit rate, and is a measure of the effectiveness of the cache.
In the case of a cache miss, most caches allocate a new entry, which comprises the tag just missed and a copy of the data from memory. The reference can then be applied to the new entry just as in the case of a hit. Misses are comparatively slow because they require the data to be transferred from main memory. This transfer incurs a delay since main memory is much slower than cache memory, and also incurs the overhead for recording the new data in the cache before it is delivered to the processor.



Processor with instructions that operate on different data types stored in the same single logical register file

A processor with instructions to operate on different data types stored in a single logical register file. According to one aspect of the invention, a first set of instructions of a first instruction type operates on the contents of what at least logically appears to software as a single logical register file. The first set of instructions appears to access the single logical register file as a flat register file. In addition, a first instruction of a second instruction type operates on the logical register file. However, the first instruction appears to access the logical register file as a stack referenced register file. Furthermore, sometime between starting the execution of the first set of instructions and completing the execution of the first instruction, all tags in a set of tags indicating whether corresponding registers in the single logical register file are empty or non-empty are caused to indicate non-empty states.

Integrated data processing system having CPU core and parallel independently operating DSP module utilizing successive approximation analog to digital and PWM for parallel disconnect

An integrated data processing system includes a shared internal bus for transferring both instructions and data. A shared bus interface unit is connected to the shared internal bus and connectable via a shared external bus to a shared external memory array such that instructions and data held in the shared external memory array are transferrable to the shared internal bus via the shared bus interface unit. A general purpose (GP) central processing unit (CPU) is connected to the shared internal bus for retrieving GP instructions. The GP CPU includes an execution unit for executing GP instructions to process data retrieved by the GP CPU from the shared internal bus. A digital signal processor (DSP) module connected to the shared internal bus, the DSP module includes a signal processor for processing an externally-provided digital signal received by the DSP module by executing DSP command-list instructions. Execution of DSP command-list code instructions by the DSP module is independent of and in parallel with execution of GP instructions by the GP CPU. A shared internal memory that holds command-list code instructions and is connected for access by the DSP module for retrieval of command-list code instructions for execution by the DSP module and for access by the GP CPU for storage and retrieval of instructions and data.