Achronix ACE Version 5.0 - Manual (Page 284)

Analyzing Critical Paths Chapter 4. Tasks
Analyzing Critical Paths
Critical paths are computed by timing analysis. Timing analysis can be run at several points in the flow , as
indicated in the Flow view . Timing analysis can be repeated with different implementation options without
having to re-run the rest of the flow, by double-clicking the appropriate Run . . . Timing Analysis flow step .
The results of timing analysis are shown in a Timing Report , which is automatically displayed as timing
analysis completes. Critical paths are also shown in the Critical Paths view and the Critical Path Diagram
view . (While users may view an old timing report 8 at any time, the Critical Path views only show the paths
from the last time that timing analysis was run within a given ACE session.)
Generating Timing Reports
A timing report is generated and displayed in the GUI whenever one of the Run . . . Timing Analysis flow
steps is run. Timing reports may also be generated at any time from Tcl by running the appropriate flow
step ( run -step flow step name ) or with the run timing analysis command.
Timing reports can be found in the implementation’s reports directory, available for browsing via the
Projects view . In addition to the HTML report files displayed in the GUI, there are equivalent report files in
text and csv (spreadsheet) formats.
The Timing Analysis implementation options in the Options view determine how timing analysis is run and
which parts of the timing report are generated.
Synchronous Target Devices
The amount of information in the Details section of the report will be altered by implementation options in
the Options view . See Synchronous Timing Reports for more details.
Critical paths will also be displayed in the Critical Paths view . The Path ID can be used to cross-reference
between the Critical Paths view and the timing reports.
Asynchronous Target Devices
For each of the three sections in the report, users may specify the number of critical paths that should be
found; be aware that finding more paths requires more runtime. In some cases fewer paths are found than
were requested this happens when all remaining paths would be of the hardware limit variety.
Each path in the report has an ID of the form current 1, current 2, etc., for part I (the current results);
potential 1, potential 2 for part II (the potential results); and detail 1, detail 2 for part III (the clock domain
details). These IDs match the names listed in the
Critical Paths view . For reconvergent and unbalanced
complex paths, the Critical Paths view lists each forward and backward segment separately. The Critical
Path Diagram view is especially helpful for understanding the geometry of reconvergent and complex
paths.
The XP Table option (Make an XP table, available for part II and part III,) adds a table to the timing report
that shows the relation between potential XP values and frequency. This option has no effect on the critical
paths listed in the report.
Highlighting Critical Paths
To highlight a routed 9 critical path in the Floorplanner view :
1. First, run one of the timing analysis flow steps to generate critical path data.
2. Then, in the Critical Paths view , browse through all reported critical paths.
• Synchronous devices: By default, highlight colors of setup/hold violations are arranged in a
gradient from red to yellow according to the slack’s distance from zero. Paths with a positive
slack (setup/hold met) are colored green by default.
8 previously generated timing reports will be available in every implementation’s reports directory
9 paths which are not routed cannot be displayed in the Floorplanner
UG001 Rev. 5.0 - 5th December 2012 http://www.achronix.com 272