The current support for IOBUFs (#1148) requires them to be explicitly instantiated and connected directly to a top-level IO port.

Using a top-level inout port directly in the following way won't work:

inout A;

...

wire A_i;
wire A_t;
wire A_o;

assign A_i = A;
assign A = (A_t == 1'b1) ? A_o : 1'bz;

I tried to play with the iopadmap Yosys command but failed to find a working solution. In some cases I ended up with an OBUFT-like cell for the 3-state output and the input taken directly from the pin (not through any buffer). In other cases I had a properly connected IOBUF cell but after optimization its output got disconnected (a bug?).