
10–16
Altera Corporation
Stratix Device Handbook, Volume 2
July 2005
DSP Block
Stratix and Stratix GX device DSP blocks outperform LE-based
implementations for common DSP functions. Each DSP block contains
several multipliers that can be configured for widths of 9, 18, or 36 bits.
Depending on the mode of operation, these multipliers can optionally
feed an adder/subtractor/accumulator or summation unit.
You can configure the DSP block’s input registers to efficiently
implement shift registers for serial input sharing, eliminating the need for
external shift registers in LEs. You can add pipeline registers to the DSP
block for accelerated operation. Registers are available at the input and
output of the multiplier, and at the output of the
adder/subtractor/accumulator or summation block.
DSP blocks have four modes of operation:
■
Simple multiplier mode
■
Multiply-accumulator mode
■
Two-multipliers adder mode
■
Four-multipliers adder mode
Associated megafunctions are available in the Quartus II software to
implement each mode of the DSP block.
DSP Block Megafunctions
You can use the lpm_mult megafunction to configure the DSP block for
simple multiplier mode. You can set the lpm_mult Multiplier
Implementation
option in the MegaWizard Plug-In Manager to either
use the default implementation, ESBs, or the DSP blocks. If you select the
Use Default
option, the compiler first attempts to place the multiplier in
the DSP blocks. However, under certain conditions, the compiler may
implement the multiplier in LEs. The placement depends on factors such
as DSP block resource consumption, the width of the multiplier, whether
an operand is a constant, and other options chosen for the megafunction.
Stratix and Stratix GX devices do not support the Use ESBs option. If you
select this option, the Quartus II software tries to place the multiplier in
unused DSP blocks.
You can recompile APEX II or APEX 20K designs using the lpm_mult
megafunction for Stratix and Stratix GX devices in the Quartus II
software without changing the megafunction. This makes converting
lpm_mult
megafunction designs to Stratix or Stratix GX devices
straightforward.