Some io_out and io_oeb signals are buffered in caravel_core and caravan_core

[d-m-bailey]

In caravel_core the following signals are buffered

io_out[6:0]
io_oeb[6:0]

In caravan_core the following signals are buffered

io_out[0]
io_out[1]
io_out[26]
io_oeb[0]

If these signals are unconnected, there may be a leak due to Hi-Z input to inverters.

@RTimothyEdwards is recommending that these be corrected before the next tapeout. efabless/mpw_precheck#295 (comment)