优化策略之Opt_design

Available Logic Optimizations

opt_design [-retarget] [-propconst] [-sweep] [-bram_power_opt] [-remap]

[-resynth_area] [-resynth_seq_area] [-directive <arg>] [-muxf_remap]

[-hier_fanout_limit <arg>] [-bufg_opt] [-control_set_merge] [-quiet] [-verbose]

1.1 Retargeting (Default)

Retargeting replaces one cell type with another to ease optimization. For example, a MUXF7

replaced by a LUT3 can be combined with other LUTs. In addition, simple cells such as

inverters are absorbed into downstream logic.

1.2 Constant Propagation (Default)

Constant Propagation propagates constant values through logic, which results in:

• Eliminated logic:

For example, an AND with a constant 0 input

• Reduced logic:

For example, A 3-input AND with a constant 1 input is reduced to a 2-input AND.

• Redundant logic:

For example, A 2-input OR with a logic 0 input is reduced to a wire.

1.3 Sweep (Default)

Sweep removes cells that have no loads.

1.4 Block RAM Power Optimization (Default)

Block RAM Power Optimization enables power optimization on block RAM cells including:

• Changing the WRITE_MODE on unread ports of true dual-port RAMs to NO_CHANGE.

• Applying intelligent clock gating to block RAM outputs.

1.5 Remap

Remap combines multiple LUTs into a single LUT to reduce the depth of the logic.

1.6 Resynth Area

Resynth Area performs re-synthesis in area mode to reduce the number of LUTs.

1.7 Mux Optimization

Remaps MUXF7, MUXF8, and MUXF9 primitives to LUT3 to improve route-ability.

1.8 Control Set Merging

Reduce the drivers of logically-equivalent control signals to a single driver. This is like a reverse fanout replication, and results in nets that are better suited for module-based replication.

1.9 Global Clock Buffer Insertion

Logic optimization conservatively inserts global clock buffers on clock nets and high-fanout non-clock nets such as device-wide resets.

For 7 series designs, clock buffers are inserted as long as 12 total global clock buffers arenot exceeded.

For UltraScale designs, there is no limit for clock buffers inserted on clock nets.

For non-clock nets:

• Global clock buffers are only inserted as long as 24 total clock buffers are not

exceeded, not including BUFG_GT buffers.

• The fanout must be above 25,000.

For fabric-driven clock nets, the fanout must be 30 or greater.

1.10 Module-Based Fanout Optimization

Net drivers with fanout greater than the specified limit, provided as an argument with this option, will be replicated according to the logical hierarchy.

For each hierarchical instance driven by the high-fanout net, if the fanout within the hierarchy is greater than the specified limit, then the net within the hierarchy is driven by a replica of the driver of the high-fanout net

Using Directives

1

Explore

Runs multiple passes of optimization.

进行多次优化

2

ExploreArea

Runs multiple passes of optimization with emphasis on reducing combinational logic.

进行多次优化，重点是减少组合逻辑

3

AddRemap

Runs the default logic optimization flow and includes LUT remapping to reduce logic levels.

将LUT重新优化到逻辑单元内部。

4

ExploreSequentialArea

Runs multiple passes of optimization with emphasis on reducing registers and related combinational logic.

减少寄存器和组合逻辑

5

RuntimeOptimized

Runs minimal passes of optimization, trading design performance for faster run time.

更快通过优化来替代设计性能

6

NoBramPowerOpt

Runs all the default opt_design optimizations except block RAM Power Optimization.

对BRAM不做功耗优化

7

ExploreWithRemap

Same as the Explore directive but includes the Remap optimization.

与Remap类似，但是多了一个重新映射。