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Xilinx Synthesis Technology User Guide

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XST <strong>User</strong> <strong>Guide</strong><br />

Register replication is performed either for timing performance<br />

improvement or for satisfying max_fanout constraints. Register<br />

replication can be turned off using the register_duplication<br />

constraint.<br />

Following is a portion of the log file.<br />

Starting low level synthesis...<br />

Optimizing unit ...<br />

Optimizing unit ...<br />

...<br />

Optimizing unit ...<br />

Building and optimizing final netlist ...<br />

Register doc_readwrite_state_D2 equivalent to<br />

doc_readwrite_cnt_ld has been removed<br />

Register I_cci_i2c_wr_l equivalent to wr_l has been<br />

removed<br />

Register doc_reset_I_reset_out has been replicated<br />

2 time(s)<br />

Register wr_l has been replicated 2 time(s)<br />

Resource Usage<br />

In the Final Report, the Cell Usage section reports the count of all the<br />

primitives used in the design. These primitives are classified in 8<br />

groups:<br />

• BELS<br />

This group contains all the logical cells that are basic elements of<br />

the Virtex technology, for example, LUTs, MUXCY, MUXF5,<br />

MUXF6, MUXF7, MUXF8.<br />

• Flip-flops and Latches<br />

This group contains all the flip-flops and latches that are<br />

primitives of the Virtex technology, for example, FDR, FDRE, LD.<br />

• RAMS<br />

This group contains all the RAMs.<br />

• SHIFTERS<br />

This group contains all the shift registers that use the Virtex<br />

primitives. Namely SRL16, SRL16_1, SRL16E, SRL16E_1, and<br />

SLRC*.<br />

3-20 <strong>Xilinx</strong> Development System

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