wbm2axilite.v

////////////////////////////////////////////////////////////////////////////////
//
// Filename: 	wbm2axilite.v (Wishbone master to AXI slave, pipelined)
// {{{
// Project:	WB2AXIPSP: bus bridges and other odds and ends
//
// Purpose:	Convert from a wishbone master to an AXI lite interface.  The
//		big difference is that AXI lite doesn't support bursting,
//	or transaction ID's.  This actually makes the task a *LOT* easier.
//
// Creator:	Dan Gisselquist, Ph.D.
//		Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
// }}}
// Copyright (C) 2018-2021, Gisselquist Technology, LLC
// {{{
// This file is part of the WB2AXIP project.
//
// The WB2AXIP project contains free software and gateware, licensed under the
// Apache License, Version 2.0 (the "License").  You may not use this project,
// or this file, except in compliance with the License.  You may obtain a copy
// of the License at
//
//	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
// License for the specific language governing permissions and limitations
// under the License.
//
////////////////////////////////////////////////////////////////////////////////
//
//
`default_nettype	none
// }}}
module wbm2axilite #(
	parameter C_AXI_ADDR_WIDTH	=  28,// AXI Address width
	localparam C_AXI_DATA_WIDTH	=  32,// Width of the AXI R&W data
	localparam DW			=  C_AXI_DATA_WIDTH,// Wishbone data width
	localparam AW			=  C_AXI_ADDR_WIDTH-2// WB addr width (log wordsize)
	) (
	input	wire			i_clk,
	input	wire			i_reset,
	//
	// We'll share the clock and the reset
	input	wire			i_wb_cyc,
	input	wire			i_wb_stb,
	input	wire			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	wire			o_wb_stall,
	output	reg			o_wb_ack,
	output	reg	[(DW-1):0]	o_wb_data,
	output	reg			o_wb_err,
	//
	// AXI write address channel signals
	output	reg			o_axi_awvalid,
	input	wire			i_axi_awready,
	output	reg	[C_AXI_ADDR_WIDTH-1:0]	o_axi_awaddr,
	output	wire	[2:0]		o_axi_awprot,
	//
	// AXI write data channel signals
	output	reg			o_axi_wvalid,
	input	wire			i_axi_wready,
	output	reg	[C_AXI_DATA_WIDTH-1:0]	o_axi_wdata,
	output	reg	[C_AXI_DATA_WIDTH/8-1:0] o_axi_wstrb,
	//
	// AXI write response channel signals
	input	wire			i_axi_bvalid,
	output	wire			o_axi_bready,
	input	wire [1:0]		i_axi_bresp,
	//
	// AXI read address channel signals
	output	reg			o_axi_arvalid,
	input	wire			i_axi_arready,
	output	reg	[C_AXI_ADDR_WIDTH-1:0]	o_axi_araddr,
	output	wire	[2:0]		o_axi_arprot,
	//
	// AXI read data channel signals   
	input	wire			i_axi_rvalid,
	output	wire			o_axi_rready,
	input wire [C_AXI_DATA_WIDTH-1:0] i_axi_rdata,
	input	wire	[1:0]		i_axi_rresp
	);

//*****************************************************************************
// Local Parameter declarations
//*****************************************************************************

	//
	// LGIFOFLN: The log (based two) of the size of our FIFO.  This is a
	// localparam since 1) 32-bit distributed memories nearly come for
	// free, and 2) because there is no performance gain to be had in larger
	// memories.  2^32 entries is the perfect size for this application.
	// Any smaller, and the core will not be able to maintain 100%
	// throughput.
	localparam	LGFIFOLN = 5;


//*****************************************************************************
// Internal register and wire declarations
//*****************************************************************************

// Things we're not changing ...
	assign o_axi_awprot  = 3'b000;	// Unpriviledged, unsecure, data access
	assign o_axi_arprot  = 3'b000;	// Unpriviledged, unsecure, data access

	reg	full_fifo, err_state, axi_reset_state, wb_we;
	reg	[3:0]	reset_count;
	reg			pending;
	reg	[LGFIFOLN-1:0]	outstanding, err_pending;


// Master bridge logic
	assign	o_wb_stall = (full_fifo)
			||((!i_wb_we)&&( wb_we)&&(pending))
			||(( i_wb_we)&&(!wb_we)&&(pending))
			||(err_state)||(axi_reset_state)
			||(o_axi_arvalid)&&(!i_axi_arready)
			||(o_axi_awvalid)&&(!i_axi_awready)
			||(o_axi_wvalid)&&(!i_axi_wready);

	initial	axi_reset_state = 1'b1;
	initial	reset_count = 4'hf;
	always @(posedge i_clk)
	if (i_reset)
	begin
		axi_reset_state <= 1'b1;
		if (reset_count > 0)
			reset_count <= reset_count - 1'b1;
	end else if ((axi_reset_state)&&(reset_count > 0))
		reset_count <= reset_count - 1'b1;
	else begin
		axi_reset_state <= 1'b0;
		reset_count <= 4'hf;
	end

	// Count outstanding transactions
	initial	pending = 0;
	initial	outstanding = 0;
	always @(posedge i_clk)
	if ((i_reset)||(axi_reset_state))
	begin
		pending <= 0;
		outstanding <= 0;
		full_fifo <= 0;
	end else if ((err_state)||(!i_wb_cyc))
	begin
		pending <= 0;
		outstanding <= 0;
		full_fifo <= 0;
	end else case({ ((i_wb_stb)&&(!o_wb_stall)), (o_wb_ack) })
	2'b01: begin
		outstanding <= outstanding - 1'b1;
		pending <= (outstanding >= 2);
		full_fifo <= 1'b0;
		end
	2'b10: begin
		outstanding <= outstanding + 1'b1;
		pending <= 1'b1;
		full_fifo <= (outstanding >= {{(LGFIFOLN-2){1'b1}},2'b01});
		end
	default: begin end
	endcase

	always @(posedge i_clk)
	if ((i_wb_stb)&&(!o_wb_stall))
		wb_we <= i_wb_we;

	//
	//
	// Write address logic
	//
	initial	o_axi_awvalid = 0;
	always @(posedge i_clk)
	if (i_reset)
		o_axi_awvalid <= 0;
	else
		o_axi_awvalid <= (!o_wb_stall)&&(i_wb_stb)&&(i_wb_we)
			||(o_axi_awvalid)&&(!i_axi_awready);

	always @(posedge i_clk)
	if (!o_wb_stall)
		o_axi_awaddr <= { i_wb_addr, 2'b00 };

	//
	//
	// Read address logic
	//
	initial	o_axi_arvalid = 1'b0;
	always @(posedge i_clk)
	if (i_reset)
		o_axi_arvalid <= 1'b0;
	else
		o_axi_arvalid <= (!o_wb_stall)&&(i_wb_stb)&&(!i_wb_we)
			||((o_axi_arvalid)&&(!i_axi_arready));
	always @(posedge i_clk)
	if (!o_wb_stall)
		o_axi_araddr <= { i_wb_addr, 2'b00 };

	//
	//
	// Write data logic
	//
	always @(posedge i_clk)
	if (!o_wb_stall)
	begin
		o_axi_wdata <= i_wb_data;
		o_axi_wstrb <= i_wb_sel;
	end

	initial	o_axi_wvalid = 0;
	always @(posedge i_clk)
	if (i_reset)
		o_axi_wvalid <= 0;
	else
		o_axi_wvalid <= ((!o_wb_stall)&&(i_wb_stb)&&(i_wb_we))
			||((o_axi_wvalid)&&(!i_axi_wready));

	initial	o_wb_ack = 1'b0;
	always @(posedge i_clk)
	if ((i_reset)||(!i_wb_cyc)||(err_state))
		o_wb_ack <= 1'b0;
	else if (err_state)
		o_wb_ack <= 1'b0;
	else if ((i_axi_bvalid)&&(!i_axi_bresp[1]))
		o_wb_ack <= 1'b1;
	else if ((i_axi_rvalid)&&(!i_axi_rresp[1]))
		o_wb_ack <= 1'b1;
	else
		o_wb_ack <= 1'b0;

	always @(posedge i_clk)
		o_wb_data <= i_axi_rdata;

	// Read data channel / response logic
	assign	o_axi_rready = 1'b1;
	assign	o_axi_bready = 1'b1;

	initial	o_wb_err = 1'b0;
	always @(posedge i_clk)
	if ((i_reset)||(!i_wb_cyc)||(err_state))
		o_wb_err <= 1'b0;
	else if ((i_axi_bvalid)&&(i_axi_bresp[1]))
		o_wb_err <= 1'b1;
	else if ((i_axi_rvalid)&&(i_axi_rresp[1]))
		o_wb_err <= 1'b1;
	else
		o_wb_err <= 1'b0;

	initial	err_state = 1'b0;
	always @(posedge i_clk)
	if (i_reset)
		err_state <= 0;
	else if ((i_axi_bvalid)&&(i_axi_bresp[1]))
		err_state <= 1'b1;
	else if ((i_axi_rvalid)&&(i_axi_rresp[1]))
		err_state <= 1'b1;
	else if ((pending)&&(!i_wb_cyc))
		err_state <= 1'b1;
	else if (err_pending == 0)
		err_state <= 0;

	initial	err_pending = 0;
	always @(posedge i_clk)
	if (i_reset)
		err_pending <= 0;
	else case({ ((i_wb_stb)&&(!o_wb_stall)),
					((i_axi_bvalid)||(i_axi_rvalid)) })
	2'b01: err_pending <= err_pending - 1'b1;
	2'b10: err_pending <= err_pending + 1'b1;
	default: begin end
	endcase

	// Make verilator happy
	// verilator lint_off UNUSED
	wire	[2:0]	unused;
	assign	unused = { i_wb_cyc, i_axi_bresp[0], i_axi_rresp[0] };
	// verilator lint_on  UNUSED

/////////////////////////////////////////////////////////////////////////
//
//
//
// Formal methods section
//
// These are only relevant when *proving* that this translator works
//
//
//
/////////////////////////////////////////////////////////////////////////
`ifdef	FORMAL
	localparam	FIFOLN = (1<<LGFIFOLN);
	reg	f_past_valid;
//
`define	ASSUME	assume
`define	ASSERT	assert

	// Parameters
	initial	assert(DW == 32);
	initial	assert(C_AXI_ADDR_WIDTH == AW+2);
	//

	//
	// Setup
	//
	initial	f_past_valid = 1'b0;
	always @(posedge i_clk)
		f_past_valid <= 1'b1;

	always @(*)
	if (!f_past_valid)
		`ASSUME(i_reset);

	//////////////////////////////////////////////
	//
	//
	// Assumptions about the WISHBONE inputs
	//
	//
	//////////////////////////////////////////////
	always @(*)
		assume(f_past_valid || i_reset);

	wire	[(LGFIFOLN-1):0]	f_wb_nreqs, f_wb_nacks,f_wb_outstanding;
	fwb_slave #(.DW(DW),.AW(AW),
			.F_MAX_STALL(0),
			.F_MAX_ACK_DELAY(0),
			.F_LGDEPTH(LGFIFOLN),
			.F_MAX_REQUESTS(FIFOLN-2))
		f_wb(i_clk, i_reset, 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, o_wb_err,
			f_wb_nreqs, f_wb_nacks, f_wb_outstanding);

	wire	[(LGFIFOLN-1):0]	f_axi_rd_outstanding,
					f_axi_wr_outstanding,
					f_axi_awr_outstanding;

	faxil_master #(
		// .C_AXI_DATA_WIDTH(C_AXI_DATA_WIDTH),
		.C_AXI_ADDR_WIDTH(C_AXI_ADDR_WIDTH),
		.F_LGDEPTH(LGFIFOLN),
		.F_AXI_MAXWAIT(3),
		.F_AXI_MAXDELAY(3))
		f_axil(.i_clk(i_clk),
			.i_axi_reset_n((!i_reset)&&(!axi_reset_state)),
			// Write address channel
			.i_axi_awvalid(o_axi_awvalid), 
			.i_axi_awready(i_axi_awready), 
			.i_axi_awaddr( o_axi_awaddr), 
			.i_axi_awprot( o_axi_awprot), 
			// Write data channel
			.i_axi_wvalid( o_axi_wvalid),
			.i_axi_wready( i_axi_wready),
			.i_axi_wdata(  o_axi_wdata),
			.i_axi_wstrb(  o_axi_wstrb),
			// Write response channel
			.i_axi_bvalid( i_axi_bvalid),
			.i_axi_bready( o_axi_bready),
			.i_axi_bresp(  i_axi_bresp),
			// Read address channel
			.i_axi_arvalid(o_axi_arvalid),
			.i_axi_arready(i_axi_arready),
			.i_axi_araddr( o_axi_araddr),
			.i_axi_arprot( o_axi_arprot),
			// Read data channel
			.i_axi_rvalid( i_axi_rvalid),
			.i_axi_rready( o_axi_rready),
			.i_axi_rdata(  i_axi_rdata),
			.i_axi_rresp(  i_axi_rresp),
			// Counts
			.f_axi_rd_outstanding( f_axi_rd_outstanding),
			.f_axi_wr_outstanding( f_axi_wr_outstanding),
			.f_axi_awr_outstanding( f_axi_awr_outstanding)
		);

	//////////////////////////////////////////////
	//
	//
	// Assumptions about the AXI inputs
	//
	//
	//////////////////////////////////////////////


	//////////////////////////////////////////////
	//
	//
	// Assertions about the AXI4 ouputs
	//
	//
	//////////////////////////////////////////////

	// Write response channel
	always @(posedge i_clk)
		// We keep bready high, so the other condition doesn't
		// need to be checked
		assert(o_axi_bready);

	// AXI read data channel signals
	always @(posedge i_clk)
		// We keep o_axi_rready high, so the other condition's
		// don't need to be checked here
		assert(o_axi_rready);

	//
	// Let's look into write requests
	//
	initial	assert(!o_axi_awvalid);
	initial	assert(!o_axi_wvalid);
	always @(posedge i_clk)
	if ((!f_past_valid)||($past(i_reset))||($past(axi_reset_state)))
	begin
		assert(!o_axi_awvalid);
		assert(!o_axi_wvalid);
	end

	always @(posedge i_clk)
	if ((f_past_valid)&&(!$past(i_reset))
		&&($past((i_wb_stb)&&(i_wb_we)&&(!o_wb_stall))))
	begin
		// Following any write request that we accept, awvalid
		// and wvalid should both be true
		assert(o_axi_awvalid);
		assert(o_axi_wvalid);
		assert(wb_we);
	end else if ((f_past_valid)&&($past(i_reset)))
	begin
		if ($past(i_axi_awready))
			assert(!o_axi_awvalid);
		if ($past(i_axi_wready))
			assert(!o_axi_wvalid);
	end

	//
	// AXI write address channel
	//
	always @(posedge i_clk)
	if ((f_past_valid)&&($past((i_wb_stb)&&(i_wb_we)&&(!o_wb_stall))))
		assert(o_axi_awaddr == { $past(i_wb_addr[AW-1:0]), 2'b00 });

	//
	// AXI write data channel
	//
	always @(posedge i_clk)
	if ((f_past_valid)&&($past(i_wb_stb)&&(i_wb_we)&&(!$past(o_wb_stall))))
	begin
		assert(o_axi_wdata == $past(i_wb_data));
		assert(o_axi_wstrb == $past(i_wb_sel));
	end

	//
	// AXI read address channel
	//
	initial	assert(!o_axi_arvalid);
	always @(posedge i_clk)
	if ((f_past_valid)&&(!$past(i_reset))
		&&($past((i_wb_stb)&&(!i_wb_we)&&(!o_wb_stall))))
	begin
		assert(o_axi_arvalid);
		assert(o_axi_araddr == { $past(i_wb_addr), 2'b00 });
	end
	//

	//
	// AXI write response channel
	//

	//
	// AXI read data channel signals
	//
	always @(posedge i_clk)
	if ((f_past_valid)&&(($past(i_reset))||($past(axi_reset_state))))
	begin
		// Relate err_pending to outstanding
		assert(outstanding == 0);
		assert(err_pending == 0);
	end else if (!err_state)
		assert(err_pending == outstanding - ((o_wb_ack)||(o_wb_err)));

	always @(posedge i_clk)
	if ((f_past_valid)&&(($past(i_reset))||($past(axi_reset_state))))
	begin
		assert(f_axi_awr_outstanding == 0);
		assert(f_axi_wr_outstanding == 0);
		assert(f_axi_rd_outstanding == 0);

		assert(f_wb_outstanding == 0);
		assert(!pending);
		assert(outstanding == 0);
		assert(err_pending == 0);
	end else if (wb_we)
	begin
		case({o_axi_awvalid,o_axi_wvalid})
		2'b00: begin
			`ASSERT(f_axi_awr_outstanding   == err_pending);
			`ASSERT(f_axi_wr_outstanding    == err_pending);
			end
		2'b01: begin
			`ASSERT(f_axi_awr_outstanding   == err_pending);
			`ASSERT(f_axi_wr_outstanding +1 == err_pending);
			end
		2'b10: begin
			`ASSERT(f_axi_awr_outstanding+1 == err_pending);
			`ASSERT(f_axi_wr_outstanding    == err_pending);
			end
		2'b11: begin
			`ASSERT(f_axi_awr_outstanding+1 == err_pending);
			`ASSERT(f_axi_wr_outstanding +1 == err_pending);
			end
		endcase

		//
		`ASSERT(!o_axi_arvalid);
		`ASSERT(f_axi_rd_outstanding == 0);
	end else begin
		if (!o_axi_arvalid)
			`ASSERT(f_axi_rd_outstanding == err_pending);
		else
			`ASSERT(f_axi_rd_outstanding+1 == err_pending);

		`ASSERT(!o_axi_awvalid);
		`ASSERT(!o_axi_wvalid);
		`ASSERT(f_axi_awr_outstanding == 0);
		`ASSERT(f_axi_wr_outstanding == 0);
	end

	always @(*)
	if ((!i_reset)&&(i_wb_cyc)&&(!err_state))
		`ASSERT(f_wb_outstanding == outstanding);

	always @(posedge i_clk)
	if ((f_past_valid)&&(err_state))
		`ASSERT((o_wb_err)||(f_wb_outstanding == 0));

	always @(posedge i_clk)
		`ASSERT(pending == (outstanding != 0));
	//
	// Make sure we only create one request at a time
	always @(posedge i_clk)
		`ASSERT((!o_axi_arvalid)||(!o_axi_wvalid));
	always @(posedge i_clk)
		`ASSERT((!o_axi_arvalid)||(!o_axi_awvalid));
	always @(posedge i_clk)
	if (wb_we)
		`ASSERT(!o_axi_arvalid);
	else
		`ASSERT((!o_axi_awvalid)&&(!o_axi_wvalid));

	always @(*)
	if (&outstanding[LGFIFOLN-1:1])
		`ASSERT(full_fifo);
	always @(*)
		assert(outstanding < {(LGFIFOLN){1'b1}});

	// AXI cover results
	always @(*)
		cover(i_axi_bvalid && o_axi_bready);
	always @(*)
		cover(i_axi_rvalid && o_axi_rready);

	always @(posedge i_clk)
		cover(i_axi_bvalid && o_axi_bready
			&& $past(i_axi_bvalid && o_axi_bready)
			&& $past(i_axi_bvalid && o_axi_bready,2));

	always @(posedge i_clk)
		cover(i_axi_rvalid && o_axi_rready
			&& $past(i_axi_rvalid && o_axi_rready)
			&& $past(i_axi_rvalid && o_axi_rready,2));

	// AXI cover requests
	always @(posedge i_clk)
		cover(o_axi_arvalid && i_axi_arready
			&& $past(o_axi_arvalid && i_axi_arready)
			&& $past(o_axi_arvalid && i_axi_arready,2));

	always @(posedge i_clk)
		cover(o_axi_awvalid && i_axi_awready
			&& $past(o_axi_awvalid && i_axi_awready)
			&& $past(o_axi_awvalid && i_axi_awready,2));

	always @(posedge i_clk)
		cover(o_axi_wvalid && i_axi_wready
			&& $past(o_axi_wvalid && i_axi_wready)
			&& $past(o_axi_wvalid && i_axi_wready,2));

	always @(*)
		cover(i_axi_rvalid && o_axi_rready);

	// Wishbone cover results
	always @(*)
		cover(i_wb_cyc && o_wb_ack);

	always @(posedge i_clk)
		cover(i_wb_cyc && o_wb_ack
			&& $past(o_wb_ack)&&$past(o_wb_ack,2));

`endif
endmodule
`ifndef	YOSYS
`default_nettype wire
`endif