前言
组合逻辑always块中向量敏感表不全导致的警告。
流程
1.对于如下代码块：
1 always @(nstate /*or master_din or master_dout_reg*/) begin 2 //initial; 3 master_din_reg = 0; 4 master_dout = 0; 5 cs = 1'b0; 6 wr_done = 1'b0; 7 rd_done = 1'b0; 8 sck_en = 1'b0; 9 case (nstate) 10 IDEL: begin 11 cs = 1'b1; 12 wr_done = 1'b0; 13 rd_done = 1'b0; 14 end 15 LOAD: begin 16 cs = 1'b0; 17 master_din_reg = master_din; 18 end 19 SEND: begin 20 sck_en = 1'b1; 21 end 22 FINISH: begin 23 cs = 1'b1; 24 wr_done = 1'b1; 25 rd_done = 1'b1; 26 sck_en = 1'b0; 27 master_dout = master_dout_reg; 28 end 29 default: begin 30 master_din_reg = 0; 31 master_dout = 0; 32 cs = 1'b0; 33 wr_done = 1'b0; 34 rd_done = 1'b0; 35 sck_en = 1'b0; 36 end 37 endcase //case 38 end
对于master_din和变量master_dout_reg，两者在组合always块中使用读取，但没有在敏感向量表中，将会导致如下错误：
Warning (10235): Verilog HDL Always Construct warning at spi_ms.v(149): variable "master_din" is read inside the Always Construct but isn't in the Always Construct's Event Control
Warning (10235): Verilog HDL Always Construct warning at spi_ms.v(159): variable "master_dout_reg" is read inside the Always Construct but isn't in the Always Construct's Event Control
2.解决方法是补全敏感向量表，避免产生不必要的锁存器：
1 always @(nstate or master_din or master_dout_reg) begin 2 //initial; 3 master_din_reg = 0; 4 master_dout = 0; 5 cs = 1'b0; 6 wr_done = 1'b0; 7 rd_done = 1'b0; 8 sck_en = 1'b0; 9 case (nstate) 10 IDEL: begin 11 cs = 1'b1; 12 wr_done = 1'b0; 13 rd_done = 1'b0; 14 end 15 LOAD: begin 16 cs = 1'b0; 17 master_din_reg = master_din; 18 end 19 SEND: begin 20 sck_en = 1'b1; 21 end 22 FINISH: begin 23 cs = 1'b1; 24 wr_done = 1'b1; 25 rd_done = 1'b1; 26 sck_en = 1'b0; 27 master_dout = master_dout_reg; 28 end 29 default: begin 30 master_din_reg = 0; 31 master_dout = 0; 32 cs = 1'b0; 33 wr_done = 1'b0; 34 rd_done = 1'b0; 35 sck_en = 1'b0; 36 end 37 endcase //case 38 end
3.更懒的方式为直接：always @（*）
解决一切问题。
以上。