How do I specify which registers to use within the Stratix™ digital signal processing (DSP) block?

Description

The three sets of registers within the DSP block are input registers, pipeline registers (output of multiplier unit), and output registers.

If you are implementing the simple multiplier mode and using the LPM_MULT function, you can set the LPM_PIPELINE parameter to 1, 2, or 3. When set to 1, it uses the input registers. When set to 2, it uses the pipeline registers. When set to 3, it uses all 3 input, pipeline, and output registers.

For the other modes, the ALTMULT_ADD and ALTMULT_ACCUM functions have these registers specified explicitly in the MegaWizard^® Plug-In Manager.

If you want to use just the input and output registers (bypass the pipeline registers) in the simple multiplier mode, you can use the ALTMULT_ADD function, implement an independent multiplier by setting the NUMBER_OF_MULTIPLIER parameter to 1, and then explicitly specifying the appropriate register stages.