Vivado handling of partly out-of-bounds parts select

OPEN: last verified in Vivado 2017.2

Consider the following test case:

module issue_057(a, y);
  input [2:0] a;
  output [3:0] y;
  localparam [5:15] p = 51681708;
  assign y = p[15 + a -: 5];
endmodule

This is expected to set y[3]=1 for a=1, but the vivado 2014.2 synthesis output sets y[3]=0.

Crosscheck: Verific 35_463_32_140722, Modelsim 10.1e, XSim 2014.2 and Icarus Verilog (git 1572dcd) implement this correctly. Quartus 14.0 suffers from the same bug.

History:
2014-09-27 Reported bug in Xilinx Support Forum
2015-05-15 Still broken in Vivado 2015.1
2016-06-15 Still broken in Vivado 2016.2
2017-07-01 Still broken in Vivado 2017.2

← Back to VlogHammer Project Page