MATLAB DESIGN HDL CODER RELEASE NOTES User's Guide Page 101

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System Generator for DSP User Guide www.xilinx.com 101
UG640 (v 12.2) July 23, 2010
Design Styles for the DSP48
For synthesis to work, the circuit must be mappable to the DSP48 and signal bitwidths
must be less than the equivalent buses in the DPS48.
You should kept in mind that the logic synthesis tools are rapidly evolving and that
inferring DPS48 configurations is more of an art than a science. This means that some
mappable designs may not be mapped efficiently, or that the mapping results may not be
consistent. It will be necessary to inspect the post synthesis netlist using a tool similar to
Synplify Pro's gate-level technology viewer to determine if the design is being correctly
mapped. If not, it may be possible to recast it to be correctly inferred. A model of a fully
synthesizable FIR filter is located at the follwing pathname in the System Generator
software tree:
.../sysgen/examples/dsp48/synth_fir/synth_fir_tb.mdl
Designs that Use DSP48 and DSP48 Macro Blocks
DSP48 Block
The DSP48 block is effectively a wrapper for the DSP48 UNISIM primitive. Because of this,
any possible DSP48 design can be implemented. This low-level implementation however
requires an 11-bit binary opmode to be routed to the DSP48's control ports in order to
configure its function. The Constant
block has a special mode enabling it to generate a
DSP48 control field. The DSP48's parameters dialog box is used to configure the pipelining
mode of the DSP48 as well as the use of the DSP48's local interconnect buses named
PCOUT-PCIN and BCOUT-BCIN. You can try out the DSP48 block by opening the
simulink model that is located at the follwing pathname in the System Generator software
tree:
.../sysgen/examples/dsp48/dsp48_primitive.mdl
Dynamic Control of the DSP48
The DSP48 has the unique capability of being able to change its operation on a per cycle
basis. This is useful in applications where the DSP48 is used in a 'resource shared' mode
such as a FIR filter where multiple taps are implemented by the same multiplier. A simple
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