initial commit

rtl/src/mem.v

@@ -0,0 +1,161 @@
+`timescale 1ns / 1ps
+//////////////////////////////////////////////////////////////////////////////////
+// Company: 
+// Engineer: 
+// 
+// Create Date: 05.01.2021 21:53:41
+// Design Name: 
+// Module Name: mem
+// Project Name: 
+// Target Devices: 
+// Tool Versions: 
+// Description: 
+// 
+// Dependencies: 
+// 
+// Revision:
+// Revision 0.01 - File Created
+// Additional Comments:
+// 
+//////////////////////////////////////////////////////////////////////////////////
+
+// 32 bit wide rom with byte addressing (address bits 1-0 are ignored)
+module rom32 #(parameter ADDR_WIDTH = 11, DATA_WIDTH = 32)
+(
+    input wire clk,
+    input wire [ADDR_WIDTH-1:0] addr,
+    output reg [DATA_WIDTH-1:0] data_out,
+    input wire read_enable
+    );
+    
+  wire [ADDR_WIDTH-2:0] internal_addr = addr[ADDR_WIDTH-1:2];   // -> ignore bit 0
+  reg [DATA_WIDTH-1:0] rom [0:(2**(ADDR_WIDTH-2))-1];
+  
+  initial begin
+    $readmemb("rom.mem", rom);
+  end
+  
+  always @(posedge clk) data_out <= rom[internal_addr];
+  
+endmodule
+
+module ram32 #(parameter ADDR_WIDTH = 16, DATA_WIDTH = 32)
+
+(
+    input wire clk,
+    input wire [ADDR_WIDTH-1:0] addr,
+    output reg [DATA_WIDTH-1:0] data_out,
+    input wire read_enable,
+    input wire [DATA_WIDTH-1:0] data_in,
+    input wire write_enable
+    );
+  
+  reg [DATA_WIDTH-1:0] ram [0:(2**(ADDR_WIDTH-2))-1];           // 32bit words with byte addressing
+  wire [ADDR_WIDTH-2:0] internal_addr = addr[ADDR_WIDTH-1:2];   // -> ignore bit 1-0
+    
+  always @(posedge clk)
+  begin
+        if(read_enable)
+            data_out <= ram[internal_addr]; 
+        if(write_enable)
+            ram[internal_addr] <= data_in;
+  end
+endmodule
+
+module mem #(parameter ADDR_WIDTH = 32,
+                parameter DATA_WIDTH = 32)
+(
+    input wire clk, rst_n,
+    input wire [ADDR_WIDTH-1:0] addr,
+    output wire [DATA_WIDTH-1:0] data_out,
+    input wire read_enable,
+    input wire [DATA_WIDTH-1:0] data_in,
+    input wire write_enable,
+    output wire io_enable,
+    input wire [DATA_WIDTH-1:0] io_rd_data,
+    output wire mem_wait,
+
+    output wire [ADDR_WIDTH-1:0] dram_addr,
+    input wire [DATA_WIDTH-1:0]  dram_read_data,
+    output wire [DATA_WIDTH-1:0] dram_write_data,
+    output wire                  dram_read_enable,
+    output wire                  dram_write_enable,
+    input wire                   dram_wait
+    );
+  
+  wire [DATA_WIDTH-1:0] ram_out, rom_out, dram_out;
+
+  // address map:
+  // ROM $0000 - $07FF 2K
+  // IO  $0800 - $0FFF 2K
+  // RAM1 $1000 - $FFFF 60K
+  // RAM2 $10000 - $FFFFFFFF ~4GB
+
+  wire ram_cs = addr[ADDR_WIDTH-1:12] != { {(ADDR_WIDTH-12){1'b0}}};
+  wire ram1_cs = ram_cs && (addr[ADDR_WIDTH-1:16] == { {(ADDR_WIDTH-16){1'b0}}});
+  wire ram2_cs = ram_cs && !ram1_cs;
+  wire rom_cs = !ram_cs && addr[11] == 1'b0;
+  wire io_cs = !ram_cs && addr[11]  == 1'b1;
+
+  assign io_enable = io_cs;
+
+  wire ram_read  = ram1_cs && read_enable;
+  wire ram_write = ram1_cs && write_enable;
+  wire rom_read  = rom_cs && read_enable;
+
+  reg [DATA_WIDTH-1:0] data_buf;
+  
+  localparam SEL_RAM1 = 0;
+  localparam SEL_RAM2 = 1;
+  localparam SEL_ROM = 2;
+  localparam SEL_IO  = 3;
+  localparam SEL_ERR = 4;
+
+  reg [1:0] out_sel;
+
+  // test
+  reg [1:0] wait_state;
+
+  ram32 #(.ADDR_WIDTH(16)) ram0  // 64KB RAM
+  (
+    .clk(clk),
+    .addr(addr[15:0]),
+    .data_out(ram_out),
+    .read_enable(ram_read),
+    .data_in(data_in),
+    .write_enable(ram_write)
+  );
+  
+  rom32 #(.ADDR_WIDTH(11)) rom0  // 2KB ROM
+  (
+    .clk(clk),
+    .addr(addr[10:0]),
+    .data_out(rom_out),
+    .read_enable(rom_read)
+  );
+
+    assign dram_out = dram_read_data;
+    assign dram_addr = addr;
+    assign dram_write_data = data_in;
+    assign dram_read_enable = ram2_cs & read_enable;
+    assign dram_write_enable = ram2_cs & write_enable;
+
+    assign data_out =   (out_sel == SEL_RAM1 ) ? ram_out :
+                        (out_sel == SEL_RAM2 ) ? dram_out :
+                        (out_sel == SEL_ROM ) ? rom_out :
+                        (out_sel == SEL_IO )  ? io_rd_data :
+                        data_buf;
+
+    assign mem_wait = ram2_cs && dram_wait;
+
+    always @(posedge clk)
+    begin
+        data_buf <= data_out;
+        if(read_enable) out_sel <=
+                            ram1_cs ? SEL_RAM1 :
+                            ram2_cs ? SEL_RAM2:
+                            rom_cs ? SEL_ROM :
+                            io_cs  ? SEL_IO :
+                            SEL_ERR;
+    end
+endmodule