| // Copyright lowRISC contributors. |
| // Licensed under the Apache License, Version 2.0, see LICENSE for details. |
| // SPDX-License-Identifier: Apache-2.0 |
| // |
| // Supports writing a field that enables |
| // a function within a module. |
| // Requirements are that the function will |
| // only be enabled when the field is written |
| // the it is the inverse of the current field |
| // setting. The can only toggle between the |
| // the on value and the off value. |
| |
| |
| module entropy_src_field_en #( |
| parameter int FieldW = 4, |
| parameter int FieldEnVal = 'ha |
| ) ( |
| input logic clk_i , |
| input logic rst_ni, |
| input logic wvalid_i, |
| input logic [FieldW-1:0] wdata_i, |
| |
| output logic enable_o |
| ); |
| |
| // signal |
| logic field_update; |
| logic [FieldW-1:0] field_value; |
| logic [FieldW-1:0] field_value_invert; |
| |
| // flops |
| logic [FieldW-1:0] field_q, field_d; |
| |
| assign field_value = FieldEnVal; |
| assign field_value_invert = ~field_value; |
| |
| always_ff @(posedge clk_i or negedge rst_ni) begin |
| if (!rst_ni) begin |
| field_q <= field_value_invert; |
| end else begin |
| field_q <= field_d; |
| end |
| end |
| |
| assign field_update = wvalid_i && (field_q == ~wdata_i) && |
| ((wdata_i == field_value) || |
| (wdata_i == field_value_invert)); |
| |
| assign field_d = field_update ? wdata_i : field_q; |
| |
| assign enable_o = (field_q == field_value); |
| |
| |
| endmodule |