Wildcards
There is a certain confusion regarding how wildcards are matched in the SDC file (in fact, by the Tcl commands), which is why full paths are often used. This causes overloaded SDC files that don’t survive changes in the hierarchy.
For example, regarding get_pins, the SDC and TimeQuest API Reference Manual page 2-15 states that pipe characters (“|”) are treated as special characters, and are therefore not matched against the “*” wildcard in the default mode. So by default, the full path has to be given, except for specific strings within hierarchies.
The -hierarchical flag somewhat helps by allowing relative names (skip the beginning of the path).
For a classic Tcl match, where ‘*’ can match a pipe character, use -compatibility_mode.
But what about get_clocks?
Experimenting
One significant advantage of Tcl scripting over Xilinx’ UCF is that one can try out the expressions in a Tcl shell. Some basics can be found in page 3-17 of the Quartus II Handbook, vol.1, chapter 3.
More inspiration can be taken from the examples in the SDC and TimeQuest API Reference Manual. It may also be helpful to look at the Quartus II Scripting Reference Manual.
From the command line, using the “-s” flag:
$ quartus_sta -s
After the welcome note, open the project (after fitting) and create a timing netlist:
tcl> project_open myproject
tcl> create_timing_netlist
tcl> read_sdc
tcl> update_timing_netlist
for effectively opening myproject.qsf. The two latter are required for get_clocks to work. One can go e.g.
tcl> get_clocks -long_help
to get some help (same text as in the manuals).
It’s possible to test what matches which command. For example, to list the PLL-derived clocks (based upon the signal’s name):
tcl> set mypins [ get_pins -compatibility_mode *|divclk ]
tcl> foreach_in_collection pin $mypins { puts [get_pin_info -name $pin] }
The Tcl shell will print something like “_col0″ in the middle to indicate that a collection has been set up. This collection is accessed through $mypins. The second command prints the matched pins to the console.
Or for those who prefer one-liners (all pins on top-level):
tcl> query_collection -all [ get_pins * ]
The “-all” flag overrides the default limit of 20 elements. To have each printed on a separate line,
tcl> foreach i [ query_collection -all [ get_pins * ] ] { puts "Pin: $i" }
The counterpart for “-all” is “-limit 1″, which fetches only the first element.
So what about get_clocks?
Listing all clocks in the design on separate lines:
tcl> foreach i [ query_collection -all [ get_clocks ] ] { puts "$i" }
Or, using “join” instead of “foreach”:
tcl> join [ query_collection -all [ get_clocks ] ] "\n"
If nothing is printed, and instead it says
Warning (332173): Ignored filter: * could not be matched with a clock
it’s most likely because read_sdc and update_timing_netlist haven’t been issued, as mentioned above.
tcl> foreach i [ query_collection -all [ get_clocks *|vga_pll|*|divclk] ] { puts $i }
which, surprisingly enough worked in the convenient way: The wildcards matched pipe characters, so one can, in fact, use this simple format in SDC files, e.g.
set_false_path -from [get_clocks *|vga_pll|*|divclk] -to [get_clocks *|bus_pll|*|divclk] set_false_path -from [get_clocks *|bus_pll|*|divclk] -to [get_clocks *|vga_pll|*|divclk]
for setting up false paths between two clocks that are derived from a common reference with PLLs.