From 7c9fc23f7e728bfa1277cb6e31d86af0f2e1c1b8 Mon Sep 17 00:00:00 2001
From: jl7719 <jl7719@ic.ac.uk>
Date: Sun, 29 Nov 2020 17:06:18 +0900
Subject: [PATCH] Update mips_cpu_data_memory.v to mips_cpu_memory.v

---
 rtl/mips_cpu_data_memory.v | 52 -------------------------------
 rtl/mips_cpu_memory.v      | 64 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 52 deletions(-)
 delete mode 100644 rtl/mips_cpu_data_memory.v
 create mode 100644 rtl/mips_cpu_memory.v

diff --git a/rtl/mips_cpu_data_memory.v b/rtl/mips_cpu_data_memory.v
deleted file mode 100644
index b2bd196..0000000
--- a/rtl/mips_cpu_data_memory.v
+++ /dev/null
@@ -1,52 +0,0 @@
-/*  
-Data Memory for Harvard Interface
-- RAM Size: 32 x 2^32 = 32 x 4294967296
-- Zero-cycle / combinatorial reads
-- Instruction in binaries or hex -> RAM_INIT_FILE
-
-Needs checking with:
--- clk_enable input being used instead of clk
--- whether there is a more efficient way of initialising memory to zero (line 32)
--- how to implement given that you cannot read and write in the same cycle (line 48)
--- special memory locations: 0x00000000 (CPU halt), 0xBFC00000 (start execution after reset)
-        -> Should PC be 0xBFC00000 at the start and 0x00000000 at the end?
-        -> And should instructions start from 0xBFC00000?
-        -> Put halt instruction at 0x00000000 by default? - What is the halt instruction?
-*/
-
-module mips_cpu_data_memory(
-    input logic clk_enable,
-    input logic[31:0] data_address,
-    input logic data_write,
-    input logic data_read,
-    input logic[31:0] data_writedata,
-    output logic[31:0] data_readdata
-);
-    parameter RAM_INIT_FILE = "";
-
-    reg [31:0] memory [4294967295:0];
-
-    initial begin
-        integer i;
-        /* Initialise to zero by default */
-        for (i=0; i<4294967296; i++) begin
-            memory[i]=0;
-        end
-        /* Load contents from file if specified */
-        if (RAM_INIT_FILE != "") begin
-            $display("RAM : INIT : Loading RAM contents from %s", RAM_INIT_FILE);
-            $readmemh(RAM_INIT_FILE, memory);
-        end
-    end
-
-    /* Combinatorial read path. */
-    assign data_readdata = data_read ? memory[data_address] : 16'hxxxx;
-
-    /* Synchronous write path */
-    always_ff @(posedge clk_enable) begin
-        //$display("RAM : INFO : data_read=%h, data_addr = %h, mem=%h", data_read, data_address, memory[data_address]);
-        if (!data_read & data_write) begin
-            memory[data_address] <= data_writedata;
-        end
-    end
-endmodule
\ No newline at end of file
diff --git a/rtl/mips_cpu_memory.v b/rtl/mips_cpu_memory.v
new file mode 100644
index 0000000..631d766
--- /dev/null
+++ b/rtl/mips_cpu_memory.v
@@ -0,0 +1,64 @@
+/*  
+Memory for Harvard Interface
+- RAM Size: 32 x 2^32 = 32 x 4294967296
+- Instructions in binaries or hex -> RAM_INIT_FILE
+- combinatorial read/fetch of instruction via instr_ port
+- combinatorial read and single cycle write of data via data_ port
+
+Instantiation of Memory Module
+- mips_cpu_memory #(RAM_INIT_FILE) ramInst(clk, data_address, data_write, data_read, data_writedata, data_readdata, instr_address, instr_readdata);
+
+Special Memory Locations
+- Whether a particular address maps to RAM, ROM, or something else is entirely down to the top-level circuit outside your CPU.
+- special memory locations: 0x00000000 (CPU halt), 0xBFC00000 (start execution after reset)
+- PC should be 0xBFC00000 at the start and 0x00000000 at the end
+
+Needs checking with:
+-- clk or clk_enable?
+-- whether there is a more efficient way of initialising memory to zero (line 32)
+*/
+
+module mips_cpu_memory(
+    input logic clk,
+
+    //Data Memory
+    input logic[31:0] data_address,
+    input logic data_write,
+    input logic data_read,
+    input logic[31:0] data_writedata,
+    output logic[31:0] data_readdata,
+
+    //Instruction Memory
+    input logic[31:0] instr_address,
+    output logic[31:0] instr_readdata
+
+);
+    parameter RAM_INIT_FILE = "";
+
+    reg [31:0] memory [4294967295:0];   // 2^32 memory locations of 32 bits size
+
+    initial begin
+        integer i;
+        //Initialise to zero by default
+        for (i=0; i<4294967296; i++) begin
+            memory[i]=0;
+        end
+        //Load contents from file if specified
+        if (RAM_INIT_FILE != "") begin
+            $display("RAM : INIT : Loading RAM contents from %s", RAM_INIT_FILE);
+            $readmemh(RAM_INIT_FILE, memory);
+        end
+    end
+
+    //Combinatorial read path for data and instruction.
+    assign data_readdata = data_read ? memory[data_address] : 16'hxxxx;
+    assign instr_readdata = memory[instr_address]
+
+    //Synchronous write path
+    always_ff @(posedge clk) begin
+        //$display("RAM : INFO : data_read=%h, data_addr = %h, mem=%h", data_read, data_address, memory[data_address]);
+        if (!data_read & data_write) begin  //cannot read and write to memory in the same cycle
+            memory[data_address] <= data_writedata;
+        end
+    end
+endmodule
\ No newline at end of file