A section cache system designed for VLIW architectures
The static specification of operations executed in parallel using No Operations (NOPs) is another culprit to make code size to be increased in VLIW architecture. Some alternatives in the instruction encoding and memory subsystem are proposed to minimize the impact of NOP on the code size. One is the compressed cache using the packed encoding scheme and the other is the decompressed cache using the unpacked encoding scheme. The compressed cache shows high memory utilization but increases the pipeline branch penalty because it requires very complex fetch hardware. On the contrary, the fetch overhead can be decreased in the decompressed cache because the unpacked encoding scheme allows an instruction to be issued to the pipeline without any recovery process. However, it has a shortcoming that the memory utilization is deteriorated due to the memory allocation irrespective of the number of useful operations. In this research, a new instruction encoding scheme called a semi-packed encoding scheme and the section cache, which enables effective store and retrieval of semi-packed instructions, are proposed. This can decrease the hardware complexity to fetch an instruction and the wasted memory space due to NOPs via the partially fixed length of an instruction. The experimental results reveal that the memory utilization in the section cache is 3.4 times higher than in the decompressed cache. The memory subsystem using the section cache can provide about 15% performance improvement with the moderate size of chip area. (C) 2000 Elsevier Science B.V. All rights reserved.
cache vliw instruction encoding scheme memory hierarchy performance evaluation