NIOS II DMIPS

Matthew mentioned that the next release of Nios II will have better multiply support for cyclone devices.

Note that it will also have support for fast shift/rotates. This was enabled by mux enhancements to

Quartus 4.1 (available to all users).

As for current multiply performance on Cyclone, the current Nios II implementations provide

no multiply hardware at all. Instead, the compiler is setup to call a function that uses other

ALU instructions to perform the multiply. This results in pretty slow multiplies.

If you really need good multiply performance in Nios II, you'll need to wait for our next release

or check out the thread elsewhere on this forum about adding a multiply custom instruction.

As for comparing Nios II multiply/shift performance on Stratix and Cyclone, the multiply performance

using LEs on Cyclone won't match the DSP multipliers on Stratix but will be much improved over

using software emulation for multiplies. This is because you can only multiply a few bits of the

multiplier operand per cycle without killing the Fmax when using LEs. So, on cyclone, it will take

multiple cycles to compute the product whereas on Stratix I/II, the dedicated DSP multipliers

do the job in 3 cycles (pipelining provides a throughput of 1 multiply per cycle).

As for shift/rotate, we expect to be able to match the Stratix performance on Cyclone.