Incomplete reset specification on external register interface

[sdnellen]

From open-register-design-tool created by petenixon: Juniper#62

Hi @sdnellen,

It looks like issue Juniper#59 is still a problem, due to various downstream physical design, gate-level simulation, and DFT issues. Please see comments in issue Juniper#59 for an explanation. We hope you can correct the issue.

Thanks,
@petenixon

[sdnellen]

OK - committed fix (190606.01) to get reset logic out of the always blocks for assign of non-reset signals (cleaned up in logic module, but missed a someof these cases in decoder). As far as need to reset signals such as addr/w, this is flow dependent and issues can be solved in other ways (have taped out multiple designs successfully including gate sim etc w/o need for this) - however, since it was fairly straightfwd, have added a systemverilog output control parameter reset_all_outputs that if set to true should add these resets (intent of parameter is to reset all similar signals, but very likely I have missed some beyond the basic external interface.

[sdnellen]

Hi Scott,

Still an issue related to Juniper#59 with 190615.01; The following code may not be synthesizable.

The latter four assignments are also triggered by reset, but shouldn't be. This would cause the synthesizer to implement with flops that have both set and clear pins, which are not broadly supported, in order to reset to the value on the _next bus. This implementation can be glitchy, due to combo logic on the input logic cone.

It would make more sense to move these assignments to a separate always block.

 //------- reg assigns for external i/f
  always_ff @ (posedge clk or negedge sig_ordtreg_rst_n) begin
    if (! sig_ordtreg_rst_n) begin
      d2h_ext_bus1_we_ex <=  1'b0;
      d2h_ext_bus1_re_ex <=  1'b0;
      d2h_ext_bus2_we_ex <=  1'b0;
      d2h_ext_bus2_re_ex <=  1'b0;
    end
    else begin
      d2h_ext_bus1_we_ex <=  d2h_ext_bus1_we_next & ~h2d_ext_bus1_ack_ex & ~h2d_ext_bus1_nack_ex;
      d2h_ext_bus1_re_ex <=  d2h_ext_bus1_re_next & ~h2d_ext_bus1_ack_ex & ~h2d_ext_bus1_nack_ex;
      d2h_ext_bus2_we_ex <=  d2h_ext_bus2_we_next & ~h2d_ext_bus2_ack_ex & ~h2d_ext_bus2_nack_ex;
      d2h_ext_bus2_re_ex <=  d2h_ext_bus2_re_next & ~h2d_ext_bus2_ack_ex & ~h2d_ext_bus2_nack_ex;
    end
    d2h_ext_bus1_w_ex <=  d2h_ext_bus1_w_next;
    d2h_ext_bus1_addr_ex <=  d2h_ext_bus1_addr_next;
    d2h_ext_bus2_w_ex <=  d2h_ext_bus2_w_next;
    d2h_ext_bus2_addr_ex <=  d2h_ext_bus2_addr_next;
  end

Thanks,
Pete

[sdnellen]

Thanks! will grab and test.

[sdnellen]

Hi Scott,
Looks like you have missed the "overflow" and "underflow" signals in the counters and
"interrupt delay signals.