always @(x or currentState)
begin
case (currentState)
S0 : ...
S1 :
case(x)
2'b01 : nextState<=S2;
default : nextState<=S0;
endcase
S2 : ...
S3 : …
default : ;
end
S0
S2
01/0
00/0
1x/0
00/1
01/1
1x/1
S1
S3
各自検討