PIP Clarifications (Xilinx#33)

* Update scoring page to mention interconnect tiles Signed-off-by: Zak Nafziger <[email protected]> * reword for clarity Co-authored-by: eddieh-xlnx <[email protected]> * move comment about pips only to details page Signed-off-by: Zak Nafziger <[email protected]> * less technical language in initial explanation Co-authored-by: eddieh-xlnx <[email protected]> * update Router section of details Signed-off-by: Zak Nafziger <[email protected]> * improve specificity in details Co-authored-by: eddieh-xlnx <[email protected]> * Mention INT prefix ahead of table * further wording changes Co-authored-by: eddieh-xlnx <[email protected]> --------- Signed-off-by: Zak Nafziger <[email protected]> Co-authored-by: eddieh-xlnx <[email protected]>
eddieh-xlnx · Oct 31, 2023 · 1cb95b9 · 1cb95b9
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diff --git a/docs/details.md b/docs/details.md
@@ -5,7 +5,7 @@
 * The target device for this contest will be the AMD/Xilinx UltraScale+ xcvu3p.
 * Competing routers must consume a pre-placed and partially-routed
  [FPGA Interchange Format](http://www.rapidwright.io/docs/FPGA_Interchange_Format.html) Physical Netlist
-  and emit a fully routed Physical Netlist.
+  and emit a fully routed Physical Netlist formed by enabling some number of routing switches (termed PIPs).
 * The exact scoring criteria is presented on the [Scoring Criteria](score.html)
   webpage. In general, contestant routers are expected, in order of importance, to:
     1. Produce a legal routing solution ...
@@ -41,8 +41,9 @@ Should contestants wish to test/train with more benchmarks than those that are p
 
 #### Router
 With just the pre-placed but partially-routed input Physical Netlist, competitors are required to route all
-signal nets while preserving all existing placement and routing. This fully-routed result must then be written
-out as a new Physical Netlist.
+signal nets while preserving all existing placement and routing. In practice this
+is achieved by only inserting FPGAIF routeSegment objects of the type `pip` into the
+netlist. This fully-routed result must then be written out as a new Physical Netlist.
 
 #### Post-routing
 Once this fully-routed Physical Netlist is ready, RapidWright takes it again and combines it with the previous

diff --git a/docs/score.md b/docs/score.md
@@ -53,10 +53,13 @@ between a BEL output pin and a BEL input pin is simply the sum of the
 wirelength of every routeSegment that must be traced through to reach the input
 from the output.
 For the purposes of the contest, only routeSegments of the type `pip` can
-affect the wirelength, since these are the only type of routeSegment that can
-be added by contest routers. All other types of routeSegment (`belPin`,
-`sitePin`, `sitePIP`) are therefore assumed to have a wirelength of zero.
-Thus for a portion of a path that looks like this:
+affect the wirelength.
+In almost all cases, these `pip` routeSegments exist in interconnect
+tiles (which have names starting with the `INT` prefix) and are the only way for
+signals to be routed between non-interconnect tiles.
+Since `pip`s are the only type of routeSegment that can connect multiple tiles, all other types of
+routeSegment (`belPin`, `sitePin`, `sitePIP`) are assumed to have a wirelength
+of zero. Thus for a portion of a path that looks like this:
 ```
 output belPin -> ... -> pip1 -> pip2 -> ... -> pipN -> ... -> input belPin
       0           0      w       x       y       z      0          0
@@ -66,7 +69,8 @@ The wirelength from the output to the input would be `w+x+y+z`.
 Each `pip` represents a connection that causes `wire0` to drive `wire1`;
 such connections incur a wirelength score based on the type of wire indicated
 by `wire1`. The following table presents regular expression patterns to be
-matched against this `wire1` name and its associated wirelength score.
+matched against the `wire1` name of PIPs with a tile name prefix of `INT`
+and its associated wirelength score.
 
 | Wire Type         | Regex Pattern           | Wirelength Score |
 |-------------------|-------------------------|------------------|