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diff --git a/docs/device_resources.md b/docs/device_resources.md index a2671c5..9793098 100644 --- a/docs/device_resources.md +++ b/docs/device_resources.md @@ -244,6 +244,25 @@ port. From there site routing continues per above.  +### Use of site PIPs + +It is important to note that site PIPs can only be used to access placed cells +inside that site. Site PIPs cannot be used as general route-thrus, to route +from site input to output. General route-thrus across entire sites should use +tile pseudo PIPs as described below - even if a site pin is being validly used +for one sink pin of a net that is located inside the site; site PIPs cannot +also be used to leave the site again to reach other sinks. + +LUT route-thrus, for example, might require both site PIPs and tile pseudo +PIPs. The site PIP would be used to route through the LUT in order to access +an associated flipflop input inside the site. The tile PIP would be used to +route across the entire site as part of the general, inter-tile, routing +problem. + +A diagram illustrating the legal and illegal uses is shown below. + + + ### Tile Types and site types To reduce data duplication in the device schema, both tiles and sites have a |