verilog语法技巧(三)–RAM的初始化

RAM可以通过以下方式初始化：

1. 在HDL源代码中指定RAM初始内容；
2. 在外部数据文件中指定RAM初始内容。
   Verilog Coding Example：

1，所有可寻址的words都初始化为相同的值

reg [DATA_WIDTH-1:0] ram [DEPTH-1:0]; 
integer i; 
initial for (i=0; i<DEPTH; i=i+1) ram[i] = 0; 
end

2,在外部数据文件中指定RAM初始内容

使用HDL源代码中的文件读取函数从外部数据文件加载RAM初始内容。
以下外部数据文件使用二进制值初始化8×32位RAM：

00001110110000011001111011000110
00101011001011010101001000100011
01110100010100011000011100001111
01000001010000100101001110010100
00001001101001111111101000101011
00101101001011111110101010100111
11101111000100111000111101101101
10001111010010011001000011101111
................................

Code Example (Verilog):

reg [31:0] ram [0:63]; 
initial begin 
$readmemb(“rams_20c.data”, ram, 0, 63); 
end

3 Initializing Block RAM (Verilog)

// Initializing Block RAM (Single-Port Block RAM) 
// File: rams_sp_rom 
module rams_sp_rom (clk, we, addr, di, dout); 
input clk; 
input we; 
input [5:0] addr; 
input [19:0] di; 
output [19:0] dout; 
reg [19:0] ram [63:0]; 
reg [19:0] dout; 
initial 
begin 
ram[63] = 20'h0200A; ram[62] = 20'h00300; ram[61] = 20'h08101; 
ram[60] = 20'h04000; ram[59] = 20'h08601; ram[58] = 20'h0233A; 
ram[57] = 20'h00300; ram[56] = 20'h08602; ram[55] = 20'h02310; 
ram[54] = 20'h0203B; ram[53] = 20'h08300; ram[52] = 20'h04002; 
ram[51] = 20'h08201; ram[50] = 20'h00500; ram[49] = 20'h04001; 
ram[48] = 20'h02500; ram[47] = 20'h00340; ram[46] = 20'h00241; 
ram[45] = 20'h04002; ram[44] = 20'h08300; ram[43] = 20'h08201; 
ram[42] = 20'h00500; ram[41] = 20'h08101; ram[40] = 20'h00602; 
ram[39] = 20'h04003; ram[38] = 20'h0241E; ram[37] = 20'h00301; 
ram[36] = 20'h00102; ram[35] = 20'h02122; ram[34] = 20'h02021; 
ram[33] = 20'h00301; ram[32] = 20'h00102; ram[31] = 20'h02222; 
ram[30] = 20'h04001; ram[29] = 20'h00342; ram[28] = 20'h0232B; 
ram[27] = 20'h00900; ram[26] = 20'h00302; ram[25] = 20'h00102; 
ram[24] = 20'h04002; ram[23] = 20'h00900; ram[22] = 20'h08201; 
ram[21] = 20'h02023; ram[20] = 20'h00303; ram[19] = 20'h02433; 
ram[18] = 20'h00301; ram[17] = 20'h04004; ram[16] = 20'h00301; 
ram[15] = 20'h00102; ram[14] = 20'h02137; ram[13] = 20'h02036; 
ram[12] = 20'h00301; ram[11] = 20'h00102; ram[10] = 20'h02237; 
ram[9] = 20'h04004; ram[8] = 20'h00304; ram[7] = 20'h04040; 
ram[6] = 20'h02500; ram[5] = 20'h02500; ram[4] = 20'h02500; 
ram[3] = 20'h0030D; ram[2] = 20'h02341; ram[1] = 20'h08201; 
ram[0] = 20'h0400D; 
end 
always @(posedge clk) 
begin 
if (we) 
ram[addr] <= di; 
dout <= ram[addr]; 
end 
endmodule

4,从外部数据文件初始化块RAM(Verilog)

// Initializing Block RAM from external data file 
// Binary data 
// File: rams_init_file.v 
module rams_init_file (clk, we, addr, din, dout); 
input clk; 
input we; 
input [5:0] addr; 
input [31:0] din; 
output [31:0] dout; 
reg [31:0] ram [0:63]; 
reg [31:0] dout; 
initial begin 
$readmemb("rams_init_file.data",ram); 
end 
always @(posedge clk) 
begin 
if (we) 
ram[addr] <= din; 
dout <= ram[addr]; 
end 
endmodule

用于初始化RAM的外部文件需要以位向量形式。整数或十六进制格式的外部文件将无法工作。