I know this is a question which is difficult to be answered, but does anyone have an estimate which Spartan-6 fpga has comparable 'size' as a xc2v1000 or a xc2v3000 fpga? With 'size' I don't mean chip dimensions, I mean logic functionality.
I've used both V2 and S6 (among others) and find S6 is easier to meet the same frequencies with. Also S6 has much better I/O performance and a lot of features that were not available in the V2 days like SERDES on general IO pins, variable delay elements, PLL's and hard memory control blocks that allow the S6 to easily interface with DDR2 memory at
300+ MHz. even though the fabric clock rate is not much better than V2's. The 6-input LUT's help to reduce logic levels, so depending on your design requirements you could gain more speed. Also the S6 has the newer DSP48 structures instead of the simple multipliers from the V2. V2 had more DCM's and block RAM's for the same size part, but you can afford a larger S6 so you save a lot of money even if you need to move to a part with more LUTs.
In my experience, Spartan 6 runs faster than Virtex 2. In addition, you can reduce the number of logic levels because of larger LUTs. Spartan 6 also has many features that weren't introduced before Virtex 4, like DSP48's, SERDES on general I/O, variable IO delays, PLL's...
Although the Spartan 6 fabric is not a whole lot faster than V2, the hard memory controllers allow you to use faster external memory, which can reduce pin count and power over using wider slower memory. DDR2 can easily do 312 MHz (400 MHz with tweaked VCCint). Also S6 uses much less power than V2.
As noted, S6 doesn't have as much block RAM for the same fabric size, however the much lower price and lower power make it a win even if you need to use a larger S6 part to get the memory you need.
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