A flexible multiport content-addressable memory

Abstract

SUMMARYThis paper is concerned with content-addressable memory (CAM), which is a kind of functional memory. Flexible multiport content-addressable memory (FMCAM) is proposed, in which flexible retrieval functions and a multiport structure are realized. The implementation and an evaluation are presented. It is known that CAM offers high speed of the matching retrieval function. On the other hand, there are problems in practice concerning the relation between the processing speed and the number of comparators, and also the problem of cost, which have prevented its widespread use. Consequently, we developed the following FMCAM. Multiport CAM is realized by reducing the increase of the number of comparators while retaining highspeed matching retrieval functions. Functions for flexible retrieval can be added by implementation in an FPGA. By the categorization process and the use of a ring counter, multiple processing operations can be performed immediately while reducing the number of comparators. This improves the performance of the CAM itself. Another advantage is that FMCAM alone can perform the same processing in situations in which parallel CAM should be applied. After implementing the proposed FMCAM, several tests were performed for comparison. Excellent values were obtained: the AT product was 37.5% lower on average than in conventional CAM, and the increase in hardware complexity was by a factor of 1.57 even if the number of ports was increased by a factor of 4.

Application of Multi-ported CAM for Parallel Coding

“…6 shows the number of clock cycles for the Huffman encoding operation with these pictures. The adapted FMCAM is compared with a conventional DSP and the original FMCAM [1]. The encoding clock cycles with the original FMCAM are almost always smaller than with the conventional DSP even in the case of 1 port.…”

“…In [1], the FMCAM architecture has been shown to result in effective devices, indicated by their comparatively small product of implementation area and processing time (area-time product). Therefore, if this architecture is exploited to process multiple searches, it is capable to accelerate any application, and in particular parallel coding applications, such as data compression and encryption.…”

“…For improving the efficiency of the multi-ported CAM structure, we have been proposing a Flexible Multi-ported Content Addressable Memory (FMCAM) architecture [1], which is a novel functional memory for parallel search.…”

“…The multi-ported CAM effectively uses the previously reported Flexible Multi-ported Content Addressable Memory (FMCAM) technology [1] and enables the coding of multiple input symbols in parallel, while the hardware amount becomes lower than for conventional architectures.…”

An Optimal CAM-based Separated BTB for a Superscalar Processor

“…In our proposal, the CBTB uses the current BTB, and NBTB is an additional hardware. To optimize the hardware size and the performance, the structure of NBTB is tested by using an SRAM and CAM [10]- [13] because the replacement algorithms of CAM have a relationship with hardwire size and the searching hit rate of CAM. We test the replacing method by using a least recently used method (LRU) and a rotation method [14].…”