We discovered that output driver information was missing on most pins in *.lib files generated with QTM. It turns out the reason is that QTM will not add driver information to outputs that have no timing arcs. A quick fix is to add a dummy arc from one of the QTM pins declared clock (not input) to the output(s) of interest. This PR does exactly that, for all black-box pins that have a create_clock statement applied to them in the top-level synthesis constraints.
My main concern is that these dummy arcs might cause problems in the timing analysis -- please check the synthesis & PnR results to make sure that is not the case. In parallel, I can investigate whether there is a cleaner way to add this driver information. However, it is not clear that there will be, so I suggest that we use this quick fix for now.
We discovered that output driver information was missing on most pins in
*.libfiles generated with QTM. It turns out the reason is that QTM will not add driver information to outputs that have no timing arcs. A quick fix is to add a dummy arc from one of the QTM pins declared clock (not input) to the output(s) of interest. This PR does exactly that, for all black-box pins that have a create_clock statement applied to them in the top-level synthesis constraints.My main concern is that these dummy arcs might cause problems in the timing analysis -- please check the synthesis & PnR results to make sure that is not the case. In parallel, I can investigate whether there is a cleaner way to add this driver information. However, it is not clear that there will be, so I suggest that we use this quick fix for now.