When there is a constraint conflict while placing IOs, the user gets an
error message such as
ERROR: Bel 'X0/Y27/io1' of type 'SB_IO' is not valid for cell 'my_pin' of type 'SB_IO'
While this identifies the problematic cell, it does not explain why
there is a problem. Add some verbose messages to allow users to
determine where the problem is. This can result in something like
Info: Net '$PACKER_VCC_NET' for cell 'my_pin' conflicts with net 'ce' for 'ce_pin'
which provides something actionable.
Signed-off-by: Sean Anderson <seanga2@gmail.com>
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