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SOFT CELL

by Tom Cantrell

Start ę Start Making Sense ę Viva La Difference ę No Free Lunch ę Tool Sweet ę Real Time or Hard Time? ę Small Step, Big Journey ę Sources and PDF

START MAKING SENSE

With so many variations to choose from, itęs helpful to sort them out in terms of a few basic characteristics.

Obviously, as with traditional CPUs, performance is the most significant factor. Clearly, the CPU portion of a field-programmable SoC has to deliver the MIPs needed to handle the task at hand. With options ranging from tiny 8-bit programmable state machines to full-blown 32-bit number crunchers, thereęs plenty of choice.

Next up is price. Itęs simple enough to determine for hard-core chips, just look at the price sheet. For soft-cores, itęs a little more complicated. First off is the cost for the soft-core IP itself (and any required tools to make use of it), which is an up-front, indirect cost spread across the total number of units shipped. The direct unit cost for a soft-core is represented by any royalties required by the IP provider plus the dollar equivalent of that portion of the targeted FPGA consumed by the soft-core logic.

Another possibly key factor for a soft-core is portability. How easy is it (if itęs even encouraged or allowed) to migrate a soft-core to different flavors of FPGA or an ASIC? For example, I suspect Altera isnęt really interested in the concept of porting NIOS to Xilinx FPGAs.

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