High speed cam lookup using stored encoded key

Abstract

The search key and key fields of a CAM in a cache are encoded with a Hamming distance of at least two to increase the speed of the CAM by ensuring each mismatching match line is discharged by at least two transistors in parallel. Where the cache is physically tagged, the search key is a physical address. The page address portion of the physical address is encoded prior to being stored in a TLB. The page offset bits are encoded in parallel with the TLB access, and concatenated with the encoded TLB entry. If a page address addresses a large memory page size, a plurality of corresponding sub-page addresses may be generated, each addressing a smaller page size. These sub-page addresses may be encoded and stored in a micro TLB. The encoded key and key field are tolerant of single-bit soft errors.

Description

technical field [0001] The present invention relates generally to the field of electronic circuits and more particularly to a method of high-speed accessing content addressable memory using an encoded key field and a stored encoded key. Background technique [0002] Microprocessors perform computing tasks in a wide variety of applications, including embedded applications such as portable electronic devices. The ever-expanding feature set and increased functionality of such devices requires even more computationally powerful processors. Accordingly, there is a need for processor improvements that increase execution speed. [0003] Most modern processors take advantage of the spatial and temporal locality properties of most programs by storing recently executed instructions and recently accessed data in one or more cache memories for ready access by the instruction execution pipeline. A cache is a high-speed, (usually) on-chip memory structure comprising random access memory...

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Problems solved by technology

Since the small transistor 106 has a lower current carrying capacity, it takes a

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