verilog use $random, why random seed be force changed?

luoyanghero · 发表于 2020-10-3 16:31:56

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本帖最后由 luoyanghero 于 2020-10-3 16:47 编辑

//How use $random with seed?

//This is the verilog standard documentdiscription:

//The seed argument controls the numbers that$random returns so that different seeds generate different random streams. Theseed argument shall be an integral variable. The seed value should be assignedto this variable prior to calling $random.

//I did a test.

`ifndef DLY
`define DLY 1
`endif
module tb_top;
reg clk_bus;
reg brst_n;
reg [31:0] frame_cnt;
reg [31:0] cnt;
initial begin
brst_n = 1'b1;
#1;
brst_n = 1'b0;
#100;
brst_n = 1'b1;
#1000000000;
//$finish;
end
initial begin
clk_bus = 1'b0;
forever #5 clk_bus = ~clk_bus;
end
always @ (posedge clk_bus or negedge brst_n) begin
if (~brst_n)
cnt[31:0] <= #`DLY 'd0;
else
cnt[31:0] <= #`DLY cnt + 1;
end
always @ (posedge clk_bus or negedge brst_n) begin
if (~brst_n)
frame_cnt[31:0] <= #`DLY 32'd0;
else if (cnt==1000)
frame_cnt[31:0] <= #`DLY frame_cnt + 1;
end
integer end_dly;
initial begin
end_dly = 1;
while (1) begin
@(posedge clk_bus);
if (cnt==1001) begin
#`DLY end_dly = $random(frame_cnt[7:0]);//luoy why random seed(frame_cnt[7:0]) be force changed?
end
end
end
initial begin
//wait ((in_data_drv.frm_cnt == 1) && (in_data_drv.mb_y_cnt == 90));
$fsdbDumpfile("tb_top.fsdb");
$fsdbDumpvars(tb_top, 0);
end
endmodule

复制代码

//frame_cnt be force changed from 32'h1 to 32'hce.

luoyanghero · 发表于 2020-10-5 10:05:37

有人遇到过吗？

[讨论] verilog use $random, why random seed be force changed?

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