memdev.v

////////////////////////////////////////////////////////////////////////////////
//
// Filename:	memdev.v
//
// Project:	dbgbus, a collection of 8b channel to WB bus debugging protocols
//
// 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 pipeline access, although the
//	memory pipeline here still costs a cycle and there may be other cycles
//	lost between the ZipCPU (or whatever is the master of the bus) and this,
//	thus costing more cycles in access.  Either way, operations can be
//	pipelined for single cycle access on subsequent transactions.
//
//
// Creator:	Dan Gisselquist, Ph.D.
//		Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2015-2017, Gisselquist Technology, LLC
//
// This file is part of the debugging interface demonstration.
//
// The debugging interface demonstration is free software (firmware): you can
// redistribute it and/or modify it under the terms of the GNU Lesser General 
// Public License as published by the Free Software Foundation, either version
// 3 of the License, or (at your option) any later version.
//
// This debugging interface demonstration 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 Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser 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:	LGPL, v3, as defined and found on www.gnu.org,
//		http://www.gnu.org/licenses/lgpl.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	wire			i_clk, i_wb_cyc, i_wb_stb, i_wb_we;
	input	wire	[(AW-1):0]	i_wb_addr;
	input	wire	[(DW-1):0]	i_wb_data;
	input	wire	[(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;

	// Now, let's keep verilator happy
	// verilator lint_off UNUSED
	wire	unused;
	assign	unused = i_wb_cyc;
	// verilator lint_on UNUSED
endmodule