Comparison of Cache- and Scratch-Pad based Memory Systems with respect to Performance, Area and Energy Consumption

In this report we evaluate the options for low power on-chip memories during system design and configuration. Specifically, we compare the use of scratch pad memories with that of cache on the basis of performance, area and energy. The target architecture used in our experiments is the AT91M40400 microcontroller containing an ARM7TDMI core. A packing algorithm is used to map the memory objects of the benchmarks to the scratch pad. Area and energy for different scratch pad and cache sizes are computed using the CACTI tool while performance is derived using the trace results of the ARMulator. We observe area and performance improvements by using a scratch pad memory. For example, for bubble sort there is a performance improvement of 18% from a hardware which needs 34% less area. The scratch pad also needs less energy per access, due to the absence of tag comparison.