refactor: move to dpi module for memory access

npc/core/src/main/resources/RamDpi.v

@@ -0,0 +1,24 @@
+import "DPI-C" function int pmem_read(input int addr);
+import "DPI-C" function void pmem_write(input int waddr, input int wdata, input byte wmask);
+
+module RamDpi (
+  input writeEnable,
+  input valid,
+  input [31:0] writeAddr,
+  input [31:0] writeData,
+  input [3:0] writeMask,
+  input reg [31:0] readAddr,
+  output reg [31:0] readData
+);
+  always @(*) begin
+    if (valid) begin // 有读写请求时
+      readData = pmem_read(readAddr);
+      if (writeEnable) begin // 有写请求时
+        pmem_write(writeAddr, writeData, { 4'h0, writeMask });
+      end
+    end
+    else begin
+      readData = 0;
+    end
+  end
+endmodule