Example - 1

For example, consider the example Locked_override_register example. This register module supports a lock mode that blocks any writes after lock is set to 1.However, it also allows override of the lock protection when scan_mode or debug_unlocked modes are active.

lock_status <= 1'b0;

lock_status <= 1'b1;

lock_status <= lock_status
if (~resetn) // Register is reset resetnbeginendelse if (Lock)beginendelse if (~Lock)beginend


Data_out <= 16'h0000;

Data_out <= Data_in;

Data_out <= Data_out;
if (~resetn) // Register is reset resetnbeginendelse if (write & (~lock_status | scan_mode | debug_unlocked) ) // Register protected by Lock bit input, overrides supported for scan_mode & debug_unlockedbeginendelse if (~write)beginend
module Locked_register_example(input [15:0] Data_in,input Clk,input resetn,input write,input Lock,input scan_mode,input debug_unlocked,output reg [15:0] Data_out);reg lock_status;always @(posedge Clk or negedge resetn)always @(posedge Clk or negedge resetn)endmodule

If either the scan_mode or the debug_unlocked modes can be triggered by software, then the lock protection may be bypassed.

Either remove the debug and scan mode overrides or protect enabling of these modes so that only trusted and authorized users may enable these modes.