一个AES的密钥扩展模块，综合时很多WARNING:Xst:1895 ....求解

thanksoar

WARNING:Xst:1710 - FF/Latch  <r0/out_23> (without init value) has a constant value of 0 in block <aes_key_expand_128>.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch  <r0/out_22> (without init value) has a constant value of 0 in block <aes_key_expand_128>.



代码见下。。。。不知道问题出在哪。这个模块是在顶层模块下调用的，但是端口里的输入key的值是从另外一个子模块返回给顶层模块的，而且没有付初值，问题会处在这么？

1. module aes_key_expand_128(clk, kld, key, wo_0, wo_1, wo_2, wo_3);
   
2. input                clk;
   
3. input                kld;
   
4. input        [127:0]        key;
   
5. output        [31:0]        wo_0, wo_1, wo_2, wo_3;
   
6. reg        [31:0]        w[3:0];
   
7. wire        [31:0]        tmp_w;
   
8. wire        [31:0]        subword;
   
9. wire        [31:0]        rcon;
   
10. 
    
11. assign wo_0 = w[0];
    
12. assign wo_1 = w[1];
    
13. assign wo_2 = w[2];
    
14. assign wo_3 = w[3];
    
15. always @(posedge clk)        w[0] <= #1 kld ? key[127:096] : w[0]^subword^rcon;
    
16. always @(posedge clk)        w[1] <= #1 kld ? key[095:064] : w[0]^w[1]^subword^rcon;
    
17. always @(posedge clk)        w[2] <= #1 kld ? key[063:032] : w[0]^w[2]^w[1]^subword^rcon;
    
18. always @(posedge clk)        w[3] <= #1 kld ? key[031:000] : w[0]^w[3]^w[2]^w[1]^subword^rcon;
    
19. assign tmp_w = w[3];
    
20. aes_sbox u0(        .a(tmp_w[23:16]), .d(subword[31:24]));
    
21. aes_sbox u1(        .a(tmp_w[15:08]), .d(subword[23:16]));
    
22. aes_sbox u2(        .a(tmp_w[07:00]), .d(subword[15:08]));
    
23. aes_sbox u3(        .a(tmp_w[31:24]), .d(subword[07:00]));
    
24. aes_rcon r0(        .clk(clk), .kld(kld), .out(rcon));
    
25. endmodule
    
26. 
    

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