Design Considerations
You should consider the following elements in your design:
• Operational modes
• Internal coefficient and pre-adder
• Accumulator
• Chainout adder
Operational Modes
The Quartus II software includes megafunctions that you can use to control the operation mode of the
multipliers. After entering the parameter settings with the MegaWizard Plug-In Manager, the Quartus II
software automatically configures the variable precision DSP block.
Altera provides two methods for implementing various modes of the Cyclone V variable precision DSP
block in a design—using the Quartus II DSP megafunction and HDL inferring.
The following Quartus II megafunctions are supported for the Cyclone V variable precision DSP blocks
implementation:
• LPM_MULT
• ALTMULT_ADD
• ALTMULT_ACCUM
• ALTMULT_COMPLEX
Related Information
•
Introduction to Megafunction User Guide
•
Integer Arithmetic Megafunctions User Guide
•
Floating-Point Megafunctions User Guide
•
Internal Coefficient and Pre-Adder
To use the pre-adder feature, all input data and multipliers must have the same clock setting.
The input cascade support is not available when you enable the pre-adder feature.
In both 18-bit and 27-bit modes, you can use the coefficient feature and pre-adder feature independently.
Accumulator
The accumulator in the Cyclone V devices supports double accumulation by enabling the 64-bit double
accumulation registers located between the output register bank and the accumulator.
The double accumulation registers are set statically in the programming file.
Chainout Adder
You can use the output chaining path to add results from other DSP blocks.
Variable Precision DSP Blocks in Cyclone V Devices
Altera Corporation
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Design Considerations
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2014.01.10