CHISEL中的ListLookUp

Question

I am new to Scala and I have been trying to understand the RISC-V architecture. I came across this piece of code, which I have been staring at for hours, unable to understand.

val csignals =                                                                                                   
  ListLookup(io.dat.inst,                                                                                       
                         List(N, BR_N  , OP1_X  ,  OP2_X  , ALU_X   , WB_X   , REN_0, MEN_0, M_X  , MT_X,  CSR.N),
           Array(       /* val  |  BR  |  op1   |   op2     |  ALU    |  wb  | rf   | mem  | mem  | mask |  csr  */
                        /* inst | type |   sel  |    sel    |   fcn   |  sel | wen  |  en  |  wr  | type |  cmd  */
              LW      -> List(Y, BR_N  , OP1_RS1, OP2_IMI , ALU_ADD ,  WB_MEM, REN_1, MEN_1, M_XRD, MT_W,  CSR.N),
              LB      -> List(Y, BR_N  , OP1_RS1, OP2_IMI , ALU_ADD ,  WB_MEM, REN_1, MEN_1, M_XRD, MT_B,  CSR.N),
              LBU     -> List(Y, BR_N  , OP1_RS1, OP2_IMI , ALU_ADD ,  WB_MEM, REN_1, MEN_1, M_XRD, MT_BU, CSR.N),... 

1. What ListLookUp exactly does here ?
2. Is the value of 'csignals' Boolean or something else ?

Answer 1

The ListLookUp is roughly equivalent to a switch() statement in software programming, or a casez statement in Verilog RTL.

The first argument ( io.dat.inst ) is the signal to match against.

The second argument is the default value if no match occurs.

The third argument is an Array of "key"->"value" tuples. The io.dat.inst is matched against the keys to find a match and the csignals is set to the value part if a match is found.

So csignals is of a type List() .