🚀 go-pugleaf

In article <1992Oct9.185221.10612@tamsun.tamu.edu> kuttanna@eemips.tamu.edu writes:
 > I have been trying to model the shift right/left operations wherein I
 > shift a register by a variable amount (specified within the instruction).
 > [...]
 >  result = {{`SHAMT{op2[WIDTH-1]}},temp[WIDTH - `SHAMT - 1:0]};
 > 
 > I keep getting the following error message :
 > 
 > Error!    Non-constant part-select index                    [Verilog-NCPSI]
 >           "r2k.v", 560: temp[WIDTH - IR[10 : 6] - 1:0]
 > 
 > The manual says that you cannot concantenate with non-constant widths.

It not just that -- you can't have a variable part select _anywhere_.

Left shift:
result = op2 << `SHAMT;

Right shift with fill:
result = ({{`WIDTH {op2[`WIDTH - 1]}}, op2} >> `SHAMT);
//         ^^^^^^^^^^^^^^^^^^^^^^^^^ prepend lots of high bits before the shift

The is or may not Do The Right Thing in synthesis, but you get the idea.
--
Elliot H. Mednick                                        P.O. Box 150
Wellspring Solutions                                     Sutton, MA. 01590
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