【FPGA】双端口RAM的设计（同步读写）
之前的博文都是讲单端口RAM的，它们仅有一套控制输入，例如cs，we，oe，还有数据总线以及地址。
附上太多链接，我也累，自己找吧。
双端口RAM，顾名思义，有两套地址，数据总线，以及cs等。
从输入输出也可以看出来：
input clk , // Clock Input
input [ADDR_WIDTH - 1 : 0] address_0 , // address_0 Input
inout [data_0_WIDTH-1 : 0] data_0 , // data_0 bi-directional
input cs_0 , // Chip Select
input we_0 , // Write Enable/Read Enable
input oe_0 , // Output Enable
input [ADDR_WIDTH - 1 : 0] address_1 , // address_1 Input
inout [data_0_WIDTH-1 : 0] data_1 , // data_1 bi-directional
input cs_1 , // Chip Select
input we_1 , // Write Enable/Read Enable
input oe_1 // Output Enable
写部分：
//--------------Code Starts Here------------------
// Memory Write Block
// Write Operation : When we_0 = 1, cs_0 = 1
always @ (posedge clk)
begin : MEM_WRITE
if ( cs_0 && we_0 ) begin
mem[address_0] <= data_0;
end
else if (cs_1 && we_1) begin
mem[address_1] <= data_1;
end
end
读部分：
// Tri-State Buffer control
// output : When we_0 = 0, oe_0 = 1, cs_0 = 1
assign data_0 = (cs_0 && oe_0 && !we_0) ? data_0_out : 8'bz;// Memory Read Block
// Read Operation : When we_0 = 0, oe_0 = 1, cs_0 = 1
always @ (posedge clk)
begin : MEM_READ_0
if (cs_0 && !we_0 && oe_0) begin
data_0_out <= mem[address_0];
end
else begin
data_0_out <= 0;
end
end//Second Port of RAM
// Tri-State Buffer control
// output : When we_0 = 0, oe_0 = 1, cs_0 = 1
assign data_1 = (cs_1 && oe_1 && !we_1) ? data_1_out : 8'bz;
// Memory Read Block 1
// Read Operation : When we_1 = 0, oe_1 = 1, cs_1 = 1
always @ (posedge clk)
begin : MEM_READ_1
if (cs_1 && !we_1 && oe_1) begin
data_1_out <= mem[address_1];
end else begin
data_1_out <= 0;
end
end
可见，可以操作地址0以及地址1读写，因此可以实现同时读写操作。
如果对两套端口同时进行写操作，可见地址0优先，而读就不存在这种情况。（可不必考虑这句话！）
下面给出完整Verilog HDL设计代码：
`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Create Date: 2019/05/28 20:50:48
// Design Name:
// Module Name: ram_dp_sr_sw
//////////////////////////////////////////////////////////////////////////////////
module ram_dp_sr_sw #(
parameter data_0_WIDTH = 8,
parameter ADDR_WIDTH = 8,
parameter RAM_DEPTH = 1 << ADDR_WIDTH
)(
input clk , // Clock Input
input [ADDR_WIDTH - 1 : 0] address_0 , // address_0 Input
inout [data_0_WIDTH-1 : 0] data_0 , // data_0 bi-directional
input cs_0 , // Chip Select
input we_0 , // Write Enable/Read Enable
input oe_0 , // Output Enable
input [ADDR_WIDTH - 1 : 0] address_1 , // address_1 Input
inout [data_0_WIDTH-1 : 0] data_1 , // data_1 bi-directional
input cs_1 , // Chip Select
input we_1 , // Write Enable/Read Enable
input oe_1 // Output Enable
);
//--------------Internal variables----------------
reg [data_0_WIDTH-1:0] data_0_out ;
reg [data_0_WIDTH-1:0] data_1_out ;
reg [data_0_WIDTH-1:0] mem [0:RAM_DEPTH-1];
//initialization
// synopsys_translate_off
integer i;
initial begin
for(i=0; i < RAM_DEPTH; i = i + 1) begin
mem[i] = 8'h00;
end
end
// synopsys_translate_on
//--------------Code Starts Here------------------
// Memory Write Block
// Write Operation : When we_0 = 1, cs_0 = 1
always @ (posedge clk)
begin : MEM_WRITE
if ( cs_0 && we_0 ) begin
mem[address_0] <= data_0;
end
else if (cs_1 && we_1) begin
mem[address_1] <= data_1;
end
end
// Tri-State Buffer control
// output : When we_0 = 0, oe_0 = 1, cs_0 = 1
assign data_0 = (cs_0 && oe_0 && !we_0) ? data_0_out : 8'bz;
// Memory Read Block
// Read Operation : When we_0 = 0, oe_0 = 1, cs_0 = 1
always @ (posedge clk)
begin : MEM_READ_0
if (cs_0 && !we_0 && oe_0) begin
data_0_out <= mem[address_0];
end
else begin
data_0_out <= 0;
end
end
//Second Port of RAM
// Tri-State Buffer control
// output : When we_0 = 0, oe_0 = 1, cs_0 = 1
assign data_1 = (cs_1 && oe_1 && !we_1) ? data_1_out : 8'bz;
// Memory Read Block 1
// Read Operation : When we_1 = 0, oe_1 = 1, cs_1 = 1
always @ (posedge clk)
begin : MEM_READ_1
if (cs_1 && !we_1 && oe_1) begin
data_1_out <= mem[address_1];
end else begin
data_1_out <= 0;
end
end
endmodule // End of Module ram_dp_sr_sw下面对此进行测试：
过程如下：
两个端口同时对RAM初值：
端口0写，同时端口1读：
两端口同时读：
可见，读出来的数据与时钟同步。
最后给出测试文件：
`timescale 1ns / 1ps
module ram_dp_sr_sw_tb;
reg clk ; // Clock
reg [7 : 0] address_0 ; // address_0 input
wire [7 : 0] data_0 ; // data_0 bi-directional
reg cs_0 ; // Chip Select
reg we_0 ; // Write Enable/Read Enable
reg oe_0 ; // Output Enable
reg [7 : 0] address_1 ; // address_1 input
wire [7 : 0] data_1 ; // data_1 bi-directional
reg cs_1 ; // Chip Select
reg we_1 ; // Write Enable/Read Enable
reg oe_1 ; // Output Enable
initial begin
clk = 0;
forever
#2 clk = ~clk;
end
reg [7 : 0] data_in0; //写数据时候，双向总线与data_in0连接（这样做的目的是保证总线在某一时刻读和写，二者之一有效）
assign data_0 = (cs_0 && we_0 && !oe_0) ? data_in0 : 8'dz;
reg [7 : 0] data_in1; //写数据时候，双向总线与data_in1连接（这样做的目的是保证总线在某一时刻读和写，二者之一有效）
assign data_1 = (cs_1 && we_1 && !oe_1) ? data_in1 : 8'dz;
integer i = 0;
initial begin
oe_0 = 0;
oe_1 = 0;
we_0 = 0;
we_1 = 0;
cs_0 = 0;
cs_1 = 0;
address_0 = 0;
address_1 = 0;
data_in0 = 0;
data_in1 = 0;
//先读出初识值（两套地址一起读）
#4
cs_0 = 1;
cs_1 = 1;
oe_0 = 1;
oe_1 = 1;
for(i = 0; i < 256; i = i + 1) begin
@(negedge clk) begin
address_0 = i;
address_1 = i;
end
end
//地址0写，地址1读
@(negedge clk) begin
we_0 = 1;
we_1 = 0;
oe_0 = 0;
oe_1 = 1;
end
for(i = 0; i < 256; i = i + 1) begin
@(negedge clk) begin
address_0 = i;
data_in0 = data_in0 + 1;
address_1 = i;
end
end
//地址0读·，地址1读
@(negedge clk) begin
we_0 = 0;
we_1 = 0;
oe_0 = 1;
oe_1 = 1;
end
for(i = 0; i < 256; i = i + 1) begin
@(negedge clk) begin
address_0 = i;
address_1 = i;
end
end
//结束吧，片选结束
@(negedge clk) begin
cs_0 = 0;
cs_1 = 0;
end
#100 $stop;
end
ram_dp_sr_sw #(
.ADDR_WIDTH(8), //给参数
.data_0_WIDTH(8)
) u_ram(
.clk(clk),
.address_0(address_0),
.data_0(data_0),
.cs_0(cs_0),
.we_0(we_0),
.oe_0(oe_0),
.address_1(address_1),
.data_1(data_1),
.cs_1(cs_1),
.we_1(we_1),
.oe_1(oe_1)
);
endmodule 参考链接：http://www.asic-world.com/examples/verilog/ram_dp_sr_sw.html