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Next this module will look at the effects of the native Flash operating speed vs. CPU performance. The RX family uses Renesas’ 90nm flash MONOS technology having the extremely fast access time, at just a 10 nS read time, or 100MHz. Because the Flash memory can provide instructions to the RX CPU at the same rate the CPU consumes them, there is no need for memory acceleration techniques. If we examine a pipelined processor running at 30MHz coupled to a Flash memory with a native speed which is also 30MHz, there are no pipeline stalls as shown here and performance is linear with clock speed. However, once the speed of a CPU with slower flash rises above 30MHz, one wait-state must be added after the instruction fetch stage to wait on the flash. And again at every multiple of the native Flash speed. Each time reducing overall CPU performance as you can see on the graph.

PTM Published on: 2012-05-15