Command-line Options

Basic Usage

At a minimum VPR requires two command-line arguments:

vpr architecture circuit

where:

VPR will then pack, place, and route the circuit onto the specified architecture.

By default VPR will perform a binary search routing to find the minimum channel width required to route the circuit.

Detailed Command-line Options

VPR has a lot of options. The options most people will be interested in are:

In general for the other options the defaults are fine, and only people looking at how different CAD algorithms perform will try many of them. To understand what the more esoteric placer and router options actually do, see [BRM99] or download [BR96a][BR96b][BR97b][MBR00] from the author’s web page.

In the following text, values in angle brackets e.g. <int> <float> <string> <file>, should be replaced by the appropriate number, string, or file path. Values in curly braces separated by vertical bars, e.g. {on | off}, indicate all the permissible choices for an option.

Stage Options

VPR runs all stages of (pack, place, route, and analysis) if none of --pack, --place, --route or --analysis are specified.

--pack

Run packing stage

Default: off

--place

Run placement stage

Default: off

--route

Run routing stage This also implies –analysis if routing was successful.

Default: off

--analysis

Run final analysis stage (e.g. timing, power).

Default: off

Graphics Options

--disp {on | off}

Controls whether VPR’s interactive graphics are enabled. Graphics are very useful for inspecting and debugging the FPGA architecture and/or circuit implementation.

Default: off

--auto <int>

Can be 0, 1, or 2. This sets how often you must click Proceed to continue execution after viewing the graphics. The higher the number, the more infrequently the program will pause.

Default: 1

General Options

-h, --help

Display help message then exit.

--version

Display version information then exit.

--device <string>

Specifies which device layout/floorplan to use from the architecture file.

auto uses the smallest device satisfying the circuit’s resource requirements. Other values are assumed to be the names of device layouts defined in the FPGA Grid Layout section of the architecture file.

Note

If the architecture contains both <auto_layout> and <fixed_layout> specifications, specifying an auto device will use the <auto_layout>.

Default: auto

-j, --num_workers <int>

Controls how many parallel workers VPR may use:

  • 1 implies VPR will execute serially,
  • >1 implies VPR may execute in parallel with up to the specified concurency
  • 0 implies VPR may execute with up to the maximum concurrency supported by the host machine

If this option is not specified it may be set from the VPR_NUM_WORKERS environment variable; otherwise the default is used.

Note

To compile VPR to allow the usage of parallel workers, libtbb-dev must be installed in the system.

Default: 1

--timing_analysis {on | off}

Turn VPR timing analysis off. If it is off, you don’t have to specify the various timing analysis parameters in the architecture file.

Default: on

--echo_file {on | off}

Generates echo files of key internal data structures. These files are generally used for debugging vpr, and typically end in .echo

Default: off

--verify_file_digests {on | off}

Checks that any intermediate files loaded (e.g. previous packing/placement/routing) are consistent with the current netlist/architecture.

If set to on will error if any files in the upstream dependancy have been modified. If set to off will warn if any files in the upstream dependancy have been modified.

Default: on

--target_utilization <float>

Sets the target device utilization. This corresponds to the maximum target fraction of device grid-tiles to be used. A value of 1.0 means the smallest device (which fits the circuit) will be used.

Default: 1.0

--constant_net_method {global | route}

Specifies how constant nets (i.e. those driven to a constant value) are handled:

  • global: Treat constant nets as globals (not routed)
  • route: Treat constant nets as normal nets (routed)

Default: global

--clock_modeling {ideal | route | dedicated_network}

Specifies how clock nets are handled:

  • ideal: Treat clock pins as ideal (i.e. no routing delays on clocks)
  • route: Treat clock nets as normal nets (i.e. routed using inter-block routing)
  • dedicated_network: Use the architectures dedicated clock network (experimental)

Default: ideal

--exit_before_pack {on | off}

Causes VPR to exit before packing starts (useful for statistics collection).

Default: off

--strict_checks {on, off}

Controls whether VPR enforces some consistency checks strictly (as errors) or treats them as warnings.

Usually these checks indicate an issue with either the targetted architecture, or consistency issues with VPR’s internal data structures/algorithms (possibly harming optimization quality). In specific circumstances on specific architectures these checks may be too restrictive and can be turned off.

Warning

Exercise extreme caution when turning this option off – be sure you completely understand why the issue is being flagged, and why it is OK to treat as a warning instead of an error.

Default: on

Filename Options

VPR by default appends .blif, .net, .place, and .route to the circuit name provided by the user, and looks for an SDC file in the working directory with the same name as the circuit. Use the options below to override this default naming behaviour.

--circuit_file <file>

Path to technology mapped user circuit in blif format.

Note

If specified the circuit positional argument is treated as the circuit name.

See also

--circuit_format

--circuit_format {auto | blif | eblif}

File format of the input technology mapped user circuit.

Default: auto

--net_file <file>

Path to packed user circuit in net format

--place_file <file>

Path to final placement file

--route_file <file>

Path to final routing file

--sdc_file <file>

Path to SDC timing constraints file

--write_rr_graph <file>

Writes out the routing resource graph generated at the last stage of VPR into XML format

<file> describes the filename for the generated routing resource graph. The output can be read into VPR using --read_rr_graph

--read_rr_graph <file>

Reads in the routing resource graph named <file> in the VTR root directory and loads it into the placement and routing stage of VPR.

The routing resource graph overthrows all the architecture definitions regarding switches, nodes, and edges. Other information such as grid information, block types, and segment information are matched with the architecture file to ensure accuracy.

This file should be in XML format and can be easily obtained through --write_rr_graph

--outfile_prefix <string>

Prefix for output files

Netlist Options

By default VPR will remove buffer LUTs, and iteratively sweep the netlist to remove unused primary inputs/outputs, nets and blocks, until nothing else can be removed.

--absorb_buffer_luts {on | off}

Controls whether LUTs programmed as wires (i.e. implementing logical identity) should be absorbed into the downstream logic.

Usually buffer LUTS are introduced in BLIF circuits by upstream tools in order to rename signals (like assign statements in Verilog). Absorbing these buffers reduces the number of LUTs required to implement the circuit.

Ocassionally buffer LUTs are inserted for other purposes, and this option can be used to preserve them. Disabling buffer absorption can also improve the matching between the input and post-synthesis netlist/SDF.

Default: on

--const_gen_inference {none | comb | comb_seq}

Controls how constant generators are inferred/detected in the input circuit. Constant generators and the signals they drive are not considered during timing analysis.

  • none: No constant generator inference will occur. Any signals which are actually constants will be treated as non-constants.
  • comb: VPR will infer constant generators from combinational blocks with no non-constant inputs (always safe).
  • comb_seq: VPR will infer constant generators from combinational and sequential blocks with only constant inputs (usually safe).

Note

In rare circumstances comb_seq could incorrectly identify certain blocks as constant generators. This would only occur if a sequential netlist primitive has an internal state which evolves completely independently of any data input (e.g. a hardened LFSR block, embedded thermal sensor).

Default: comb_seq

--sweep_dangling_primary_ios {on | off}

Controls whether the circuits dangling primary inputs and outputs (i.e. those who do not drive, or are not driven by anything) are swept and removed from the netlist.

Disabling sweeping of primary inputs/outputs can improve the matching between the input and post-synthesis netlists. This is often useful when performing formal verification.

Default: on

--sweep_dangling_nets {on | off}

Controls whether dangling nets (i.e. those who do not drive, or are not driven by anything) are swept and removed from the netlist.

Default: on

--sweep_dangling_blocks {on | off}

Controls whether dangling blocks (i.e. those who do not drive anything) are swept and removed from the netlist.

Default: on

--sweep_constant_primary_outputs {on | off}

Controls whether primary outputs driven by constant values are swept and removed from the netlist.

Default: off

--netlist_verbosity <int>

Controls the verbosity of netlist processing (constant generator detection, swept netlist components). High values produce more detailed output.

Default: 1

Packing Options

AAPack is the packing algorithm built into VPR. AAPack takes as input a technology-mapped blif netlist consisting of LUTs, flip-flops, memories, mulitpliers, etc and outputs a .net formatted netlist composed of more complex logic blocks. The logic blocks available on the FPGA are specified through the FPGA architecture file. For people not working on CAD, you can probably leave all the options to their default values.

--connection_driven_clustering {on | off}

Controls whether or not AAPack prioritizes the absorption of nets with fewer connections into a complex logic block over nets with more connections.

Default: on

--allow_unrelated_clustering {on | off | auto}

Controls whether primitives with no attraction to a cluster may be packed into it.

Unrelated clustering can increase packing density (decreasing the number of blocks required to implement the circuit), but can significantly impact routability.

When set to auto VPR automatically decides whether to enable unrelated clustring based on the targetted device and achieved packing density.

Default: auto

--alpha_clustering <float>

A parameter that weights the optimization of timing vs area.

A value of 0 focuses solely on area, a value of 1 focuses entirely on timing.

Default: 0.75

--beta_clustering <float>

A tradeoff parameter that controls the optimization of smaller net absorption vs. the optimization of signal sharing.

A value of 0 focuses solely on signal sharing, while a value of 1 focuses solely on absorbing smaller nets into a cluster. This option is meaningful only when connection_driven_clustering is on.

Default: 0.9

--timing_driven_clustering {on|off}

Controls whether or not to do timing driven clustering

Default: on

--cluster_seed_type {blend | timing | max_inputs}

Controls how the packer chooses the first primitive to place in a new cluster.

timing means that the unclustered primitive with the most timing-critical connection is used as the seed.

max_inputs means the unclustered primitive that has the most connected inputs is used as the seed.

blend uses a weighted sum of timing criticality, the number of tightly coupled blocks connected to the primitive, and the number of its external inputs.

max_pins selects primitives with the most number of pins (which may be used, or unused).

max_input_pins selects primitives with the most number of input pins (which may be used, or unused).

blend2 An alternative blend formulation taking into account both used and unused pin counts, number of tightly coupled blocks and criticality.

Default: blend2 if timing_driven_clustering is on; max_inputs otherwise.

--clustering_pin_feasibility_filter {on | off}

Controls whether the pin counting feasibility filter is used during clustering. When enabled the clustering engine counts the number of available pins in groups/classes of mutually connected pins within a cluster. These counts are used to quickly filter out candidate primitives/atoms/molecules for which the cluster has insufficient pins to route (without performing a full routing). This reduces packing run-time.

Default: on

--balance_block_type_utilization {on, off, auto}
Controls how the packer selects the block type to which a primitive will be mapped if it can potentially map to multiple block types.
  • on : Try to balance block type utilization by picking the block type with the (currenty) lowest utilization.
  • off : Do not try to balance block type utilization
  • auto: Dynamically enabled/disabled (based on density)

Default: auto

--target_ext_pin_util { auto | <float> | <float>,<float> | <string>:<float> | <string>:<float>,<float> }

Sets the external pin utilization target (fraction between 0.0 and 1.0) during clustering. This determines how many pin the clustering engine will aim to use in a given cluster before closing it and opening a new cluster.

Setting this to 1.0 guides the packer to pack as densely as possible (i.e. it will keep adding molecules to the cluster until no more can fit). Setting this to a lower value will guide the packer to pack less densely, and instead creating more clusters. In the limit setting this to 0.0 will cause the packer to create a new cluster for each molecule.

Typically packing less densely improves routability, at the cost of using more clusters.

This option can take several different types of values:

  • auto VPR will automatically determine appropriate target utilizations.

  • <float> specifies the target input pin utilization for all block types.

    For example:

    • 0.7 specifies that all blocks should aim for 70% input pin utilization.
  • <float>,<float> specifies the target input and output pin utilizations respectively for all block types.

    For example:

    • 0.7,0.9 specifies that all blocks should aim for 70% input pin utilization, and 90% output pin utilization.
  • <string>:<float> and <string>:<float>,<float> specify the target pin utilizations for a specific block type (as above).

    For example:

    • clb:0.7 specifies that only clb type blocks should aim for 70% input pin utilization.
    • clb:0.7,0.9 specifies that only clb type blocks should aim for 70% input pin utilization, and 90% output pin utilization.

Note

If a pin utilization target is unspecified it defaults to 1.0 (i.e. 100% utilization).

For example:

  • 0.7 leaves the output pin utilization unspecified, which is equivalent to 0.7,1.0.
  • clb:0.7,0.9 leaves the pin utilizations for all other block types unspecified, so they will assume a default utilization of 1.0,1.0.

This option can also take multiple space-separated values. For example:

--target_ext_pin_util clb:0.5 dsp:0.9,0.7 0.8

would specify that clb blocks use a target input pin utilization of 50%, dsp blocks use a targets of 90% and 70% for inputs and outputs respectively, and all other blocks use an input pin utilization target of 80%.

Note

This option is only a guideline. If a molecule (e.g. a carry-chain with many inputs) would not otherwise fit into a cluster type at the specified target utilization the packer will fallback to using all pins (i.e. a target utilization of 1.0).

Note

This option requires --clustering_pin_feasibility_filter to be enabled.

Default: auto

--pack_prioritize_transitive_connectivity {on, off}

Controls whether transitive connectivity is prioritized over high-fanout connectivity during packing.

Default: on

--pack_high_fanout_threshold {auto | <int> | <string>:<int>}

Defines the threshold for high fanout nets within the packer.

This option can take several different types of values:

  • auto VPR will automatically determine appropriate thresholds.

  • <int> specifies the fanout threshold for all block types.

    For example:

    • 64 specifies that a threshold of 64 should be used for all blocks.
  • <string>:<float> specifies the the threshold for a specific block type.

    For example:

    • clb:16 specifies that clb type blocks should use a threshold of 16.

This option can also take multiple space-separated values. For example:

--pack_high_fanout_threshold 128 clb:16

would specify that clb blocks use a threshold of 16, while all other blocks (e.g. DSPs/RAMs) would use a threshold of 128.

Default: auto

--pack_transitive_fanout_threshold <int>

Packer transitive fanout threshold.

Default: 4

--pack_feasible_block_array_size <int>

This value is used to determine the max size of the priority queue for candidates that pass the early filter legality test but not the more detailed routing filter.

Default: 30

--pack_verbosity <int>

Controls the verbosity of clustering output. Larger values produce more detailed output, which may be useful for debugging architecture packing problems.

Default: 2

Placer Options

The placement engine in VPR places logic blocks using simulated annealing. By default, the automatic annealing schedule is used [BRM99][BR97b]. This schedule gathers statistics as the placement progresses, and uses them to determine how to update the temperature, when to exit, etc. This schedule is generally superior to any user-specified schedule. If any of init_t, exit_t or alpha_t is specified, the user schedule, with a fixed initial temperature, final temperature and temperature update factor is used.

--seed <int>

Sets the initial random seed used by the placer.

Default: 1

--enable_timing_computations {on | off}

Controls whether or not the placement algorithm prints estimates of the circuit speed of the placement it generates. This setting affects statistics output only, not optimization behaviour.

Default: on if timing-driven placement is specified, off otherwise.

--inner_num <float>

The number of moves attempted at each temperature is inner_num * num_blocks^(4/3) in the circuit. The number of blocks in a circuit is the number of pads plus the number of clbs. Changing inner_num is the best way to change the speed/quality tradeoff of the placer, as it leaves the highly-efficient automatic annealing schedule on and simply changes the number of moves per temperature.

Specifying -inner_num 10 will slow the placer by a factor of 10 while typically improving placement quality only by 10% or less (depends on the architecture). Hence users more concerned with quality than CPU time may find this a more appropriate value of inner_num.

Default: 1.0

--init_t <float>

The starting temperature of the anneal for the manual annealing schedule.

Default: 100.0

--exit_t <float>

The manual anneal will terminate when the temperature drops below the exit temperature.

Default: 0.01

--alpha_t <float>

The temperature is updated by multiplying the old temperature by alpha_t when the manual annealing schedule is enabled.

Default: 0.8

--fix_pins {free | random | <file.pads>}

Controls how the placer handles I/O pads during placement.

  • free: The placer can move I/O locations to optimize the placement.
  • random: Fixes I/O pads to arbitrary locations and does not allow the placer to move them during the anneal (models the effect of poor board-level I/O constraints).
  • <file.pads>: A path to a file listing the desired location of each I/O block in the netlist.

This pad location file is in the same format as a normal placement file, but only specifies the locations of I/O pads, rather than the locations of all blocks.

Default: free.

--place_algorithm {bounding_box | path_timing_driven}

Controls the algorithm used by the placer.

bounding_box focuses purely on minimizing the bounding box wirelength of the circuit.

path_timing_driven focuses on minimizing both wirelength and the critical path delay.

Default: path_timing_driven

--place_chan_width <int>

Tells VPR how many tracks a channel of relative width 1 is expected to need to complete routing of this circuit. VPR will then place the circuit only once, and repeatedly try routing the circuit as usual.

Default: 100

--place_rlim_escape <float>

The fraction of moves which are allowed to ignore the region limit. For example, a value of 0.1 means 10% of moves are allowed to ignore the region limit.

Default: 0.0

Timing-Driven Placer Options

The following options are only valid when the placement engine is in timing-driven mode (timing-driven placement is used by default).

--timing_tradeoff <float>

Controls the trade-off between bounding box minimization and delay minimization in the placer.

A value of 0 makes the placer focus completely on bounding box (wirelength) minimization, while a value of 1 makes the placer focus completely on timing optimization.

Default: 0.5

--recompute_crit_iter <int>

Controls how many temperature updates occur before the placer performs a timing analysis to update its estimate of the criticality of each connection.

Default: 1

--inner_loop_recompute_divider <int>

Controls how many times the placer performs a timing analysis to update its criticality estimates while at a single temperature.

Default: 0

--td_place_exp_first <float>

Controls how critical a connection is considered as a function of its slack, at the start of the anneal.

If this value is 0, all connections are considered equally critical. If this value is large, connections with small slacks are considered much more critical than connections with small slacks. As the anneal progresses, the exponent used in the criticality computation gradually changes from its starting value of td_place_exp_first to its final value of --td_place_exp_last.

Default: 1.0

--td_place_exp_last <float>

Controls how critical a connection is considered as a function of its slack, at the end of the anneal.

Default: 8.0

--place_delay_model {delta, delta_override}

Controls how the timing-driven placer estimates delays.

  • delta The router is used to profile delay from various locations in the grid for various differences in position
  • delta_override Like delta but also includes special overrides to ensure effects of direct connects between blocks are accounted for. This is potentially more accurate but is more complex and depending on the architecture (e.g. number of direct connects) may increase place run-time.

Default: delta

--place_delay_model_reducer {min, max, median, arithmean, geomean}

When calculating delta delays for the placment delay model how are multiple values combined?

Default: min

--place_delay_offset <float>

A constant offset (in seconds) applied to the placer’s delay model.

Default: 0.0

--place_delay_ramp_delta_threshold <float>

The delta distance beyond which –place_delay_ramp is applied. Negative values disable the placer delay ramp.

Default: -1

--place_delay_ramp_slope <float>

The slope of the ramp (in seconds per grid tile) which is applied to the placer delay model for delta distance beyond --place_delay_ramp_delta_threshold.

Default: 0.0e-9

--place_tsu_rel_margin <float>

Specifies the scaling factor for cell setup times used by the placer. This effectively controls whether the placer should try to achieve extra margin on setup paths. For example a value of 1.1 corresponds to requesting 10%% setup margin.

Default: 1.0

--place_tsu_abs_margin <float>

Specifies an absolute offest added to cell setup times used by the placer. This effectively controls whether the placer should try to achieve extra margin on setup paths. For example a value of 500e-12 corresponds to requesting an extra 500ps of setup margin.

Default: 0.0

--post_place_timing_report <file>

Name of the post-placement timing report file to generate (not generated if unspecfied).

Router Options

VPR uses a negotiated congestion algorithm (based on Pathfinder) to perform routing.

Note

By default the router performs a binary search to find the minimum routable channel width. To route at a fixed channel width use --route_chan_width.

--max_router_iterations <int>

The number of iterations of a Pathfinder-based router that will be executed before a circuit is declared unrouteable (if it hasn’t routed successfully yet) at a given channel width.

Speed-quality trade-off: reducing this number can speed up the binary search for minimum channel width, but at the cost of some increase in final track count. This is most effective if -initial_pres_fac is simultaneously increased. Increase this number to make the router try harder to route heavily congested designs.

Default: 50

--first_iter_pres_fac <float>

Similar to --initial_pres_fac. This sets the present overuse penalty factor for the very first routing iteration. --initial_pres_fac sets it for the second iteration.

Note

A value of 0.0 causes congestion to be ignored on the first routing iteration.

Default: 0.0

--initial_pres_fac <float>

Sets the starting value of the present overuse penalty factor.

Speed-quality trade-off: increasing this number speeds up the router, at the cost of some increase in final track count. Values of 1000 or so are perfectly reasonable.

Default: 0.5

--pres_fac_mult <float>

Sets the growth factor by which the present overuse penalty factor is multiplied after each router iteration.

Default: 1.3

--acc_fac <float>

Specifies the accumulated overuse factor (historical congestion cost factor).

Default: 1

--bb_factor <int>

Sets the distance (in channels) outside of the bounding box of its pins a route can go. Larger numbers slow the router somewhat, but allow for a more exhaustive search of possible routes.

Default: 3

--base_cost_type {demand_only | delay_normalized | delay_normalized_length | delay_normalized_frequency | delay_normalized_length_frequency}

Sets the basic cost of using a routing node (resource).

  • demand_only sets the basic cost of a node according to how much demand is expected for that type of node.
  • delay_normalized is similar to demand_only, but normalizes all these basic costs to be of the same magnitude as the typical delay through a routing resource.
  • delay_normalized_length like delay_normalized, but scaled by routing resource length.
  • delay_normalized_frequency like delay_normalized, but scaled inversely by routing resource frequency.
  • delay_normalized_length_frequency like delay_normalized, but scaled by routing resource length and scaled inversely by routing resource frequency.

Default: delay_normalized_length for the timing-driven router and demand_only for the breadth-first router

--bend_cost <float>

The cost of a bend. Larger numbers will lead to routes with fewer bends, at the cost of some increase in track count. If only global routing is being performed, routes with fewer bends will be easier for a detailed router to subsequently route onto a segmented routing architecture.

Default: 1 if global routing is being performed, 0 if combined global/detailed routing is being performed.

--route_type {global | detailed}

Specifies whether global routing or combined global and detailed routing should be performed.

Default: detailed (i.e. combined global and detailed routing)

--route_chan_width <int>

Tells VPR to route the circuit at the specified channel width.

Note

If the channel width is >= 0, no binary search on channel capacity will be performed to find the minimum number of tracks required for routing. VPR simply reports whether or not the circuit will route at this channel width.

Default: -1 (perform binary search for minimum routable channel width)

--min_route_chan_width_hint <int>

Hint to the router what the minimum routable channel width is.

The value provided is used to initialize the binary search for minimum channel width. A good hint may speed-up the binary search by avoiding time spent at congested channel widths which are not routable.

The algorithm is robust to incorrect hints (i.e. it continues to binary search), so the hint does not need to be precise.

This option may ocassionally produce a different minimum channel width due to the different initialization.

Force the router to check that the channel width determined by binary search is the minimum.

The binary search ocassionally may not find the minimum channel width (e.g. due to router sub-optimality, or routing pattern issues at a particular channel width).

This option attempts to verify the minimum by routing at successively lower channel widths until two consecutive routing failures are observed.

--router_algorithm {breadth_first | timing_driven}

Selects which router algorithm to use.

The breadth_first router focuses solely on routing a design successfully, while the timing_driven router focuses both on achieving a successful route and achieving good circuit speed.

The breadth-first router is capable of routing a design using slightly fewer tracks than the timing-driving router (typically 5% if the timing-driven router uses its default parameters. This can be reduced to about 2% if the router parameters are set so the timing-driven router pays more attention to routability and less to area). The designs produced by the timing-driven router are much faster, however, (2x - 10x) and it uses less CPU time to route.

Default: timing_driven

--min_incremental_reroute_fanout <int>

Incrementally re-route nets with fanout above the specified threshold.

This attempts to re-use the legal (i.e. non-congested) parts of the routing tree for high fanout nets, with the aim of reducing router execution time.

To disable, set value to a value higher than the largest fanout of any net.

Default: 16

Timing-Driven Router Options

The following options are only valid when the router is in timing-driven mode (the default).

--astar_fac <float>

Sets how aggressive the directed search used by the timing-driven router is.

Values between 1 and 2 are reasonable, with higher values trading some quality for reduced CPU time.

Default: 1.2

--max_criticality <float>

Sets the maximum fraction of routing cost that can come from delay (vs. coming from routability) for any net.

A value of 0 means no attention is paid to delay; a value of 1 means nets on the critical path pay no attention to congestion.

Default: 0.99

--criticality_exp <float>

Controls the delay - routability tradeoff for nets as a function of their slack.

If this value is 0, all nets are treated the same, regardless of their slack. If it is very large, only nets on the critical path will be routed with attention paid to delay. Other values produce more moderate tradeoffs.

Default: 1.0

--router_init_wirelength_abort_threshold <float>

The first routing iteration wirelength abort threshold. If the first routing iteration uses more than this fraction of available wirelength routing is aborted.

Default: 0.85

--incremental_reroute_delay_ripup {on, off, auto}

Controls whether incremental net routing will rip-up (and re-route) a critical connection for delay, even if the routing is legal. auto enables delay-based rip-up unless routability becomes a concern.

Default: auto

--routing_failure_predictor {safe | aggressive | off}

Controls how aggressive the router is at predicting when it will not be able to route successfully, and giving up early. Using this option can significantly reduce the runtime of a binary search for the minimum channel width.

safe only declares failure when it is extremely unlikely a routing will succeed, given the amount of congestion existing in the design.

aggressive can further reduce the CPU time for a binary search for the minimum channel width but can increase the minimum channel width by giving up on some routings that would succeed.

off disables this feature, which can be useful if you suspect the predictor is declaring routing failure too quickly on your architecture.

Default: safe

--routing_budgets_algorithm { disable | minimax | scale_delay }

Warning

Experimental

Controls how the routing budgets are created. Routing budgets are used to guid VPR’s routing algorithm to consider both short path and long path timing constraints [FBC08].

disable is used to disable the budget feature. This uses the default VPR and ignores hold time constraints.

minimax sets the minimum and maximum budgets by distributing the long path and short path slacks depending on the the current delay values. This uses the routing cost valleys and Minimax-PERT algorithm [YLS92][FBC08].

scale_delay has the minimum budgets set to 0 and the maximum budgets is set to the delay of a net scaled by the pin criticality (net delay/pin criticality).

Default: disable

--save_routing_per_iteration {on, off}

Controls whether VPR saves the current routing to a file after each routing iteration. May be helpful for debugging.

Default: off

--congested_routing_iteration_threshold CONGESTED_ROUTING_ITERATION_THRESHOLD

Controls when the router enters a high effort mode to resolve lingering routing congestion. Value is the fraction of max_router_iterations beyond which the routing is deemed congested.

Default: 1.0 (never)

--route_bb_update {static, dynamic}

Controls how the router’s net bounding boxes are updated:

  • static : bounding boxes are never updated
  • dynamic: bounding boxes are updated dynamically as routing progresses (may improve routability of congested designs)

Default: dynamic

--router_high_fanout_threshold ROUTER_HIGH_FANOUT_THRESHOLD

Specifies the net fanout beyond which a net is considered high fanout. Values less than zero disable special behaviour for high fanout nets.

Default: 64

--router_lookahead {classic, map}

Controls what lookahead the router uses to calculate cost of completing a connection.

  • classic: The classic VPR lookahead
  • map: A more advanced lookahead which accounts for diverse wire types and their connectivity

Default: classic

--router_max_convergence_count <float>

Controls how many times the router is allowed to converge to a legal routing before halting. If multiple legal solutions are found the best quality implementation is used.

Default: 1

--router_reconvergence_cpd_threshold <float>

Specifies the minimum potential CPD improvement for which the router will continue to attempt re-convergent routing.

For example, a value of 0.99 means the router will not give up on reconvergent routing if it thinks a > 1% CPD reduction is possible.

Default: 0.99
--router_first_iter_timing_report <file>

Name of the timing report file to generate after the first routing iteration completes (not generated if unspecfied).

--router_debug_net <int>

Note

This option is likely only of interest to developers debugging the routing algorithm

Controls which net the router produces detailed debug information for.

  • For values >= 0, the value is the net ID for which detailed router debug information should be produced.
  • For value == -1, detailed router debug information is produced for all nets.
  • For values < -1, no router debug output is produced.

Warning

VPR must have been compiled with VTR_ENABLE_DEBUG_LOGGING on to get any debug output from this option.

Default: -2

--router_debug_sink_rr ROUTER_DEBUG_SINK_RR

Note

This option is likely only of interest to developers debugging the routing algorithm

Controls when router debugging is enabled for the specified sink RR.

  • For values >= 0, the value is taken as the sink RR Node ID for which to enable router debug output.
  • For values < 0, sink-based router debug output is disabled.

Warning

VPR must have been compiled with VTR_ENABLE_DEBUG_LOGGING on to get any debug output from this option.

Default: -2

Analysis Options

--full_stats

Print out some extra statistics about the circuit and its routing useful for wireability analysis.

Default: off

--gen_post_synthesis_netlist { on | off }

Generates the Verilog and SDF files for the post-synthesized circuit. The Verilog file can be used to perform functional simulation and the SDF file enables timing simulation of the post-synthesized circuit.

The Verilog file contains instantiated modules of the primitives in the circuit. Currently VPR can generate Verilog files for circuits that only contain LUTs, Flip Flops, IOs, Multipliers, and BRAMs. The Verilog description of these primitives are in the primitives.v file. To simulate the post-synthesized circuit, one must include the generated Verilog file and also the primitives.v Verilog file, in the simulation directory.

If one wants to generate the post-synthesized Verilog file of a circuit that contains a primitive other than those mentioned above, he/she should contact the VTR team to have the source code updated. Furthermore to perform simulation on that circuit the Verilog description of that new primitive must be appended to the primitives.v file as a separate module.

Default: off

--timing_report_npaths <int>

Controls how many timing paths are reported.

Note

The number of paths reported may be less than the specified value, if the circuit has fewer paths.

Default: 100

--timing_report_detail { netlist | aggregated | detailed }

Controls the level of detail included in generated timing reports.

We obtained the following results using the k6_frac_N10_frac_chain_mem32K_40nm.xml architecture and multiclock.blif circuit.

  • netlist: Timing reports show only netlist primitive pins.

    For example:

    #Path 2
    Startpoint: FFC.Q[0] (.latch clocked by clk)
    Endpoint  : out:out1.outpad[0] (.output clocked by virtual_io_clock)
    Path Type : setup
    
    Point                                                             Incr      Path
    --------------------------------------------------------------------------------
    clock clk (rise edge)                                            0.000     0.000
    clock source latency                                             0.000     0.000
    clk.inpad[0] (.input)                                            0.000     0.000
    FFC.clk[0] (.latch)                                              0.042     0.042
    FFC.Q[0] (.latch) [clock-to-output]                              0.124     0.166
    out:out1.outpad[0] (.output)                                     0.550     0.717
    data arrival time                                                          0.717
    
    clock virtual_io_clock (rise edge)                               0.000     0.000
    clock source latency                                             0.000     0.000
    clock uncertainty                                                0.000     0.000
    output external delay                                            0.000     0.000
    data required time                                                         0.000
    --------------------------------------------------------------------------------
    data required time                                                         0.000
    data arrival time                                                         -0.717
    --------------------------------------------------------------------------------
    slack (VIOLATED)                                                          -0.717
    
  • aggregated: Timing reports show netlist pins, and an aggregated summary of intra-block and inter-block routing delays.

    For example:

    #Path 2
    Startpoint: FFC.Q[0] (.latch at (3,3) clocked by clk)
    Endpoint  : out:out1.outpad[0] (.output at (3,4) clocked by virtual_io_clock)
    Path Type : setup
    
    Point                                                             Incr      Path
    --------------------------------------------------------------------------------
    clock clk (rise edge)                                            0.000     0.000
    clock source latency                                             0.000     0.000
    clk.inpad[0] (.input at (4,2))                                   0.000     0.000
    | (intra 'io' routing)                                           0.042     0.042
    | (inter-block routing)                                          0.000     0.042
    | (intra 'clb' routing)                                          0.000     0.042
    FFC.clk[0] (.latch at (3,3))                                     0.000     0.042
    | (primitive '.latch' Tcq_max)                                   0.124     0.166
    FFC.Q[0] (.latch at (3,3)) [clock-to-output]                     0.000     0.166
    | (intra 'clb' routing)                                          0.045     0.211
    | (inter-block routing)                                          0.491     0.703
    | (intra 'io' routing)                                           0.014     0.717
    out:out1.outpad[0] (.output at (3,4))                            0.000     0.717
    data arrival time                                                          0.717
    
    clock virtual_io_clock (rise edge)                               0.000     0.000
    clock source latency                                             0.000     0.000
    clock uncertainty                                                0.000     0.000
    output external delay                                            0.000     0.000
    data required time                                                         0.000
    --------------------------------------------------------------------------------
    data required time                                                         0.000
    data arrival time                                                         -0.717
    --------------------------------------------------------------------------------
    slack (VIOLATED)                                                          -0.717
    

    where each line prefixed with | (pipe character) represent a sub-delay of an edge within the timing graph.

    For instance:

    FFC.Q[0] (.latch at (3,3)) [clock-to-output]                     0.000     0.166
    | (intra 'clb' routing)                                          0.045     0.211
    | (inter-block routing)                                          0.491     0.703
    | (intra 'io' routing)                                           0.014     0.717
    out:out1.outpad[0] (.output at (3,4))                            0.000     0.717
    

    indicates that between the netlist pins FFC.Q[0] and out:out1.outpad[0] there are delays of:

    • 45 ps from the .latch output pin to an output pin of a clb block,
    • 491 ps through the general inter-block routing fabric, and
    • 14 ps from the input pin of a io block to .output.

    Also note that a connection between two pins can be contained within the same clb block, and does not use the general inter-block routing network. As an example from a completely different circuit-architecture pair:

    n1168.out[0] (.names)                                            0.000     0.902
    | (intra 'clb' routing)                                          0.000     0.902
    top^finish_FF_NODE.D[0] (.latch)                                 0.000     0.902
    
  • detailed: Like aggregated, the timing reports show netlist pins, and an aggregated summary of intra-block. In addition, it includes a detailed breakdown of the inter-block routing delays.

    It is important to note that detailed timing report can only list the components of a non-global net, otherwise, it reports inter-block routing as well as an incremental delay of 0, just as in the aggregated and netlist reports.

    For example:

    #Path 2
    Startpoint: FFC.Q[0] (.latch at (3,3) clocked by clk)
    Endpoint  : out:out1.outpad[0] (.output at (3,4) clocked by virtual_io_clock)
    Path Type : setup
    
    Point                                                             Incr      Path
    --------------------------------------------------------------------------------
    clock clk (rise edge)                                            0.000     0.000
    clock source latency                                             0.000     0.000
    clk.inpad[0] (.input at (4,2))                                   0.000     0.000
    | (intra 'io' routing)                                           0.042     0.042
    | (inter-block routing:global net)                               0.000     0.042
    | (intra 'clb' routing)                                          0.000     0.042
    FFC.clk[0] (.latch at (3,3))                                     0.000     0.042
    | (primitive '.latch' Tcq_max)                                   0.124     0.166
    FFC.Q[0] (.latch at (3,3)) [clock-to-output]                     0.000     0.166
    | (intra 'clb' routing)                                          0.045     0.211
    | (OPIN:1479 side:TOP (3,3))                                     0.000     0.211
    | (CHANX:2073 unnamed_segment_0 length:1 (3,3)->(2,3))           0.095     0.306
    | (CHANY:2139 unnamed_segment_0 length:0 (1,3)->(1,3))           0.075     0.382
    | (CHANX:2040 unnamed_segment_0 length:1 (2,2)->(3,2))           0.095     0.476
    | (CHANY:2166 unnamed_segment_0 length:0 (2,3)->(2,3))           0.076     0.552
    | (CHANX:2076 unnamed_segment_0 length:0 (3,3)->(3,3))           0.078     0.630
    | (IPIN:1532 side:BOTTOM (3,4))                                  0.072     0.703
    | (intra 'io' routing)                                           0.014     0.717
    out:out1.outpad[0] (.output at (3,4))                            0.000     0.717
    data arrival time                                                          0.717
    
    clock virtual_io_clock (rise edge)                               0.000     0.000
    clock source latency                                             0.000     0.000
    clock uncertainty                                                0.000     0.000
    output external delay                                            0.000     0.000
    data required time                                                         0.000
    --------------------------------------------------------------------------------
    data required time                                                         0.000
    data arrival time                                                         -0.717
    --------------------------------------------------------------------------------
    slack (VIOLATED)                                                          -0.717
    

    where each line prefixed with | (pipe character) represent a sub-delay of an edge within the timing graph. In the detailed mode, the inter-block routing has now been replaced by the net components.

    For OPINS and IPINS, this is the format of the name: | (ROUTING_RESOURCE_NODE_TYPE:ROUTING_RESOURCE_NODE_ID side:SIDE (START_COORDINATES)->(END_COORDINATES))

    For CHANX and CHANY, this is the format of the name: | (ROUTING_RESOURCE_NODE_TYPE:ROUTING_RESOURCE_NODE_ID SEGMENT_NAME length:LENGTH (START_COORDINATES)->(END_COORDINATES))

    Here is an example of the breakdown:

    FFC.Q[0] (.latch at (3,3)) [clock-to-output]                     0.000     0.166
    | (intra 'clb' routing)                                          0.045     0.211
    | (OPIN:1479 side:TOP (3,3))                                     0.000     0.211
    | (CHANX:2073 unnamed_segment_0 length:1 (3,3)->(2,3))           0.095     0.306
    | (CHANY:2139 unnamed_segment_0 length:0 (1,3)->(1,3))           0.075     0.382
    | (CHANX:2040 unnamed_segment_0 length:1 (2,2)->(3,2))           0.095     0.476
    | (CHANY:2166 unnamed_segment_0 length:0 (2,3)->(2,3))           0.076     0.552
    | (CHANX:2076 unnamed_segment_0 length:0 (3,3)->(3,3))           0.078     0.630
    | (IPIN:1532 side:BOTTOM (3,4))                                  0.072     0.703
    | (intra 'io' routing)                                           0.014     0.717
    out:out1.outpad[0] (.output at (3,4))                            0.000     0.717
    

    indicates that between the netlist pins FFC.Q[0] and out:out1.outpad[0] there are delays of:

    • 45 ps from the .latch output pin to an output pin of a clb block,
    • 0 ps from the clb output pin to the CHANX:2073 wire,
    • 95 ps from the CHANX:2073 to the CHANY:2139 wire,
    • 75 ps from the CHANY:2139 to the CHANX:2040 wore,
    • 95 ps from the CHANX:2040 to the CHANY:2166 wire,
    • 76 ps from the CHANY:2166 to the CHANX:2076 wire,
    • 78 ps from the CHANX:2076 to the input pin of a io block,
    • 14 ps input pin of a io block to .output.

    In the initial description we referred to the existence of global nets, which also occur in this net:

    clk.inpad[0] (.input at (4,2))                                   0.000     0.000
    | (intra 'io' routing)                                           0.042     0.042
    | (inter-block routing:global net)                               0.000     0.042
    | (intra 'clb' routing)                                          0.000     0.042
    FFC.clk[0] (.latch at (3,3))                                     0.000     0.042
    

    Global nets are unrouted nets, and their route trees happen to be null.

    Finally, is interesting to note that the consecutive channel components may not seem to connect. There are two types of occurences:

    1. The preceding channel’s ending coordinates extend past the following channel’s starting coordinates (example from a different path):
    | (chany:2113 unnamed_segment_0 length:2 (1, 3) -> (1, 1))       0.116     0.405
    | (chanx:2027 unnamed_segment_0 length:0 (1, 2) -> (1, 2))       0.078     0.482
    

    It is possible that by opening a switch between (1,2) to (1,1), CHANY:2113 actually only extends from (1,3) to (1,2).

    1. The preceding channel’s ending coordinates have no relation to the following channel’s starting coordinates. There is no logical contradiction, but for clarification, it is best to see an explanation of the VPR coordinate system. The path can also be visualized by VPR graphics, as an illustration of this point:
../../_images/path_2.png

Fig. 31 Illustration of Path #2 with insight into the coordinate system.

Fig. 31 shows the routing resources used in Path #2 and their locations on the FPGA.

  1. The signal emerges from near the top-right corner of the block to_FFC (OPIN:1479) and joins the topmost horizontal segment of length 1 (CHANX:2073).

  2. The signal proceeds to the left, then connects to the outermost, blue vertical segment of length 0 (CHANY:2139).

  3. The signal continues downward and attaches to the horizontal segment of length 1 (CHANX:2040).

  4. Of the aforementioned horizontal segment, after travelling one linear unit to the right, the signal jumps on a vertical segment of length 0 (CHANY:2166).

  5. The signal travels upward and promptly connects to a horizontal segment of length 0 (CHANX:2076).

  6. This segment connects to the green destination io (3,4).

    Default: netlist

--timing_report_skew { on | off }

Controls whether clock skew timing reports are generated.

Default: off

Power Estimation Options

The following options are used to enable power estimation in VPR.

See also

Power Estimation for more details.

--power

Enable power estimation

Default: off

--tech_properties <file>

XML File containing properties of the CMOS technology (transistor capacitances, leakage currents, etc). These can be found at $VTR_ROOT/vtr_flow/tech/, or can be created for a user-provided SPICE technology (see Power Estimation).

--activity_file <file>

File containing signal activites for all of the nets in the circuit. The file must be in the format:

<net name1> <signal probability> <transition density>
<net name2> <signal probability> <transition density>
...

Instructions on generating this file are provided in Power Estimation.