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////////////////////////////////////////////////////////////////////////////////
//
// Filename:	memdev.v
//
// Project:	CMod S6 System on a Chip, ZipCPU demonstration Project
//
// Purpose:	This file is really simple: it creates an on-chip memory,
//		accessible via the wishbone bus, that can be used in this
//	project.  The memory has single cycle access--although getting to the
//	memory from the ZipCPU may cost another cycle or two in access.  Either
//	way, operations can be pipelined for greater speed.
//
//
// Creator:	Dan Gisselquist, Ph.D.
//		Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2015-2017, Gisselquist Technology, LLC
//
// This program is free software (firmware): you can redistribute it and/or
// modify it under the terms of  the GNU General Public License as published
// by the Free Software Foundation, either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program.  (It's in the $(ROOT)/doc directory, run make with no
// target there if the PDF file isn't present.)  If not, see
// <http://www.gnu.org/licenses/> for a copy.
//
// License:	GPL, v3, as defined and found on www.gnu.org,
//		http://www.gnu.org/licenses/gpl.html
//
//
////////////////////////////////////////////////////////////////////////////////
//
//
module	memdev(i_clk, i_wb_cyc, i_wb_stb, i_wb_we, i_wb_addr, i_wb_data, i_wb_sel,
		o_wb_ack, o_wb_stall, o_wb_data);
	parameter	LGMEMSZ=15, DW=32, EXTRACLOCK= 0;
	localparam	AW = LGMEMSZ - 2;
	input				i_clk, i_wb_cyc, i_wb_stb, i_wb_we;
	input		[(AW-1):0]	i_wb_addr;
	input		[(DW-1):0]	i_wb_data;
	input		[(DW/8-1):0]	i_wb_sel;
	output	reg			o_wb_ack;
	output	wire			o_wb_stall;
	output	reg	[(DW-1):0]	o_wb_data;
 
	wire			w_wstb, w_stb;
	wire	[(DW-1):0]	w_data;
	wire	[(AW-1):0]	w_addr;
	wire	[(DW/8-1):0]	w_sel;
 
	generate
	if (EXTRACLOCK == 0)
	begin
 
		assign	w_wstb = (i_wb_stb)&&(i_wb_we);
		assign	w_stb  = i_wb_stb;
		assign	w_addr = i_wb_addr;
		assign	w_data = i_wb_data;
		assign	w_sel  = i_wb_sel;
 
	end else begin
 
		reg		last_wstb, last_stb;
		always @(posedge i_clk)
			last_wstb <= (i_wb_stb)&&(i_wb_we);
		always @(posedge i_clk)
			last_stb <= (i_wb_stb);
 
		reg	[(AW-1):0]	last_addr;
		reg	[(DW-1):0]	last_data;
		reg	[(DW/8-1):0]	last_sel;
		always @(posedge i_clk)
			last_data <= i_wb_data;
		always @(posedge i_clk)
			last_addr <= i_wb_addr;
		always @(posedge i_clk)
			last_sel <= i_wb_sel;
 
		assign	w_wstb = last_wstb;
		assign	w_stb  = last_stb;
		assign	w_addr = last_addr;
		assign	w_data = last_data;
		assign	w_sel  = last_sel;
	end endgenerate
 
	reg	[(DW-1):0]	mem	[0:((1<<AW)-1)];
 
	always @(posedge i_clk)
		o_wb_data <= mem[w_addr];
	always @(posedge i_clk)
	begin
		if ((w_wstb)&&(w_sel[3]))
			mem[w_addr][31:24] <= w_data[31:24];
		if ((w_wstb)&&(w_sel[2]))
			mem[w_addr][23:16] <= w_data[23:16];
		if ((w_wstb)&&(w_sel[1]))
			mem[w_addr][15: 8] <= w_data[15:8];
		if ((w_wstb)&&(w_sel[0]))
			mem[w_addr][ 7: 0] <= w_data[7:0];
	end
 
	always @(posedge i_clk)
		o_wb_ack <= (w_stb);
	assign	o_wb_stall = 1'b0;
 
endmodule