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axiempty.v
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axiempty.v
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////////////////////////////////////////////////////////////////////////////////
//
// Filename: axiempty.v
// {{{
// Project: WB2AXIPSP: bus bridges and other odds and ends
//
// Purpose: A basic AXI core to provide a response to an AXI master when
// no other slaves are connected to the bus. All results are
// bus errors.
//
// Creator: Dan Gisselquist, Ph.D.
// Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
// }}}
// Copyright (C) 2019-2021, 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 axiempty #(
// {{{
parameter integer C_AXI_ID_WIDTH = 2,
parameter integer C_AXI_DATA_WIDTH = 32,
// Verilator lint_off UNUSED
parameter integer C_AXI_ADDR_WIDTH = 6
// Verilator lint_on UNUSED
// Some useful short-hand definitions
// localparam AW = C_AXI_ADDR_WIDTH,
// localparam DW = C_AXI_DATA_WIDTH
// }}}
) (
// {{{
input wire S_AXI_ACLK,
input wire S_AXI_ARESETN,
//
input wire S_AXI_AWVALID,
output wire S_AXI_AWREADY,
input wire [C_AXI_ID_WIDTH-1:0] S_AXI_AWID,
//
input wire S_AXI_WVALID,
output wire S_AXI_WREADY,
input wire S_AXI_WLAST,
//
output wire S_AXI_BVALID,
input wire S_AXI_BREADY,
output wire [C_AXI_ID_WIDTH-1:0] S_AXI_BID,
output wire [1:0] S_AXI_BRESP,
//
input wire S_AXI_ARVALID,
output wire S_AXI_ARREADY,
input wire [C_AXI_ID_WIDTH-1:0] S_AXI_ARID,
input wire [7:0] S_AXI_ARLEN,
//
output wire S_AXI_RVALID,
input wire S_AXI_RREADY,
output wire [C_AXI_ID_WIDTH-1:0] S_AXI_RID,
output wire [C_AXI_DATA_WIDTH-1:0] S_AXI_RDATA,
output wire S_AXI_RLAST,
output wire [1:0] S_AXI_RRESP
// }}}
);
localparam IW = C_AXI_ID_WIDTH;
// Double buffer the write response channel only
reg [IW-1 : 0] axi_bid;
reg axi_bvalid;
////////////////////////////////////////////////////////////////////////
//
// Write logic
// {{{
////////////////////////////////////////////////////////////////////////
//
//
//
// Start with the two skid buffers
// {{{
wire m_awvalid, m_wvalid;
wire m_awready, m_wready, m_wlast;
wire [IW-1:0] m_awid;
//
skidbuffer #(.DW(IW), .OPT_OUTREG(1'b0))
awskd(S_AXI_ACLK, !S_AXI_ARESETN,
S_AXI_AWVALID, S_AXI_AWREADY, S_AXI_AWID,
m_awvalid, m_awready, m_awid );
skidbuffer #(.DW(1), .OPT_OUTREG(1'b0))
wskd(S_AXI_ACLK, !S_AXI_ARESETN,
S_AXI_WVALID, S_AXI_WREADY, S_AXI_WLAST,
m_wvalid, m_wready, m_wlast );
// }}}
// m_awready, m_wready
// {{{
// The logic here is pretty simple--accept a write address burst
// into the skid buffer, then leave it there while the write data comes
// on. Once we get to the last write data element, accept both it and
// the address. This spares us the trouble of counting out the elements
// in the write burst.
//
assign m_awready= (m_awvalid && m_wvalid && m_wlast)
&& (!S_AXI_BVALID || S_AXI_BREADY);
assign m_wready = !m_wlast || m_awready;
// }}}
// bvalid
// {{{
// As soon as m_awready above, a packet has come through successfully.
// Acknowledge it with a bus error.
//
initial axi_bvalid = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
axi_bvalid <= 1'b0;
else if (m_awready)
axi_bvalid <= 1'b1;
else if (S_AXI_BREADY)
axi_bvalid <= 1'b0;
// }}}
// bid
// {{{
always @(posedge S_AXI_ACLK)
if (m_awready)
axi_bid <= m_awid;
// }}}
assign S_AXI_BVALID = axi_bvalid;
assign S_AXI_BID = axi_bid;
assign S_AXI_BRESP = 2'b11; // An interconnect bus error
// }}}
////////////////////////////////////////////////////////////////////////
//
// Read half
// {{{
////////////////////////////////////////////////////////////////////////
//
//
reg [IW-1:0] rid, axi_rid;
reg axi_arready, axi_rlast, axi_rvalid;
reg [8:0] axi_rlen;
// axi_arready
// {{{
initial axi_arready = 1;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
axi_arready <= 1;
else if (S_AXI_ARVALID && S_AXI_ARREADY)
axi_arready <= (S_AXI_ARLEN==0)&&(!S_AXI_RVALID|| S_AXI_RREADY);
else if (!S_AXI_RVALID || S_AXI_RREADY)
begin
if ((!axi_arready)&&(S_AXI_RVALID))
axi_arready <= (axi_rlen <= 2);
end
// }}}
// axi_rlen
// {{{
initial axi_rlen = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
axi_rlen <= 0;
else if (S_AXI_ARVALID && S_AXI_ARREADY)
axi_rlen <= (S_AXI_ARLEN+1)
+ ((S_AXI_RVALID && !S_AXI_RREADY) ? 1:0);
else if (S_AXI_RREADY && S_AXI_RVALID)
axi_rlen <= axi_rlen - 1;
// }}}
// rid
// {{{
always @(posedge S_AXI_ACLK)
if (S_AXI_ARREADY)
rid <= S_AXI_ARID;
// }}}
// axi_rvalid
// {{{
initial axi_rvalid = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
axi_rvalid <= 0;
else if (S_AXI_ARVALID || (axi_rlen > 1))
axi_rvalid <= 1;
else if (S_AXI_RREADY)
axi_rvalid <= 0;
// }}}
// axi_rid
// {{{
always @(posedge S_AXI_ACLK)
if (!S_AXI_RVALID || S_AXI_RREADY)
begin
if (S_AXI_ARVALID && S_AXI_ARREADY)
axi_rid <= S_AXI_ARID;
else
axi_rid <= rid;
end
// }}}
// axi_rlast
// {{{
initial axi_rlast = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_RVALID || S_AXI_RREADY)
begin
if (S_AXI_ARVALID && S_AXI_ARREADY)
axi_rlast <= (S_AXI_ARLEN == 0);
else if (S_AXI_RVALID)
axi_rlast <= (axi_rlen == 2);
else
axi_rlast <= (axi_rlen == 1);
end
// }}}
//
assign S_AXI_ARREADY = axi_arready;
assign S_AXI_RVALID = axi_rvalid;
assign S_AXI_RID = axi_rid;
assign S_AXI_RDATA = 0;
assign S_AXI_RRESP = 2'b11;
assign S_AXI_RLAST = axi_rlast;
// }}}
// Make Verilator happy
// {{{
// Verilator lint_off UNUSED
wire unused;
assign unused = &{ 1'b0 };
// Verilator lint_on UNUSED
// }}}
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
//
// Formal properties
// {{{
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
`ifdef FORMAL
//
// The following properties are only some of the properties used
// to verify this core
//
reg f_past_valid;
initial f_past_valid = 0;
always @(posedge S_AXI_ACLK)
f_past_valid <= 1;
always @(*)
if (!f_past_valid)
assume(!S_AXI_ARESETN);
faxi_slave #(
// {{{
.C_AXI_ID_WIDTH(C_AXI_ID_WIDTH),
.C_AXI_DATA_WIDTH(C_AXI_DATA_WIDTH),
.C_AXI_ADDR_WIDTH(C_AXI_ADDR_WIDTH)
// }}}
f_slave(
// {{{
.i_clk(S_AXI_ACLK),
.i_axi_reset_n(S_AXI_ARESETN),
//
// Address write channel
//
.i_axi_awvalid(S_AXI_AWVALID),
.i_axi_awready(S_AXI_AWREADY),
.i_axi_awid( S_AXI_AWID),
.i_axi_awaddr( {(C_AXI_ADDR_WIDTH){1'b0}}),
.i_axi_awlen( S_AXI_AWLEN),
.i_axi_awsize( LSB[2:0]),
.i_axi_awburst(2'b0),
.i_axi_awlock( 1'b0),
.i_axi_awcache(4'h0),
.i_axi_awprot( 3'h0),
.i_axi_awqos( 4'h0),
//
//
//
// Write Data Channel
//
// Write Data
.i_axi_wdata({(C_AXI_DATA_WIDTH){1'b0}}),
.i_axi_wstrb({(C_AXI_DATA_WIDTH/8){1'b0}}),
.i_axi_wlast(S_AXI_WLAST),
.i_axi_wvalid(S_AXI_WVALID),
.i_axi_wready(S_AXI_WREADY),
//
//
// Response ID tag. This signal is the ID tag of the
// write response.
.i_axi_bvalid(S_AXI_BVALID),
.i_axi_bready(S_AXI_BREADY),
.i_axi_bid( S_AXI_BID),
.i_axi_bresp( S_AXI_BRESP),
//
//
//
// Read address channel
//
.i_axi_arvalid(S_AXI_ARVALID),
.i_axi_arready(S_AXI_ARREADY),
.i_axi_arid( S_AXI_ARID),
.i_axi_araddr( {(C_AXI_ADDR_WIDTH){1'b0}}),
.i_axi_arlen( S_AXI_ARLEN),
.i_axi_arsize( LSB[2:0]),
.i_axi_arburst(2'b00),
.i_axi_arlock( 1'b0),
.i_axi_arcache(4'h0),
.i_axi_arprot( 3'h0),
.i_axi_arqos( 4'h0),
//
//
//
// Read data return channel
//
.i_axi_rvalid(S_AXI_RVALID),
.i_axi_rready(S_AXI_RREADY),
.i_axi_rid(S_AXI_RID),
.i_axi_rdata(S_AXI_RDATA),
.i_axi_rresp(S_AXI_RRESP),
.i_axi_rlast(S_AXI_RLAST),
//
// ...
// }}}
);
//
////////////////////////////////////////////////////////////////////////
//
// Write induction properties
//
////////////////////////////////////////////////////////////////////////
//
// {{{
//
// ...
//
// }}}
////////////////////////////////////////////////////////////////////////
//
// Read induction properties
//
////////////////////////////////////////////////////////////////////////
//
// {{{
//
// ...
//
always @(posedge S_AXI_ACLK)
if (f_past_valid && $rose(S_AXI_RLAST))
assert(S_AXI_ARREADY);
// }}}
////////////////////////////////////////////////////////////////////////
//
// Contract checking
//
////////////////////////////////////////////////////////////////////////
//
// {{{
//
// ...
//
// }}}
////////////////////////////////////////////////////////////////////////
//
// Cover properties
//
////////////////////////////////////////////////////////////////////////
//
// {{{
reg f_wr_cvr_valid, f_rd_cvr_valid;
initial f_wr_cvr_valid = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
f_wr_cvr_valid <= 0;
else if (S_AXI_AWVALID && S_AXI_AWREADY && S_AXI_AWLEN > 4)
f_wr_cvr_valid <= 1;
always @(*)
cover(!S_AXI_BVALID && axi_awready && !m_awvalid
&& f_wr_cvr_valid /* && ... */));
initial f_rd_cvr_valid = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
f_rd_cvr_valid <= 0;
else if (S_AXI_ARVALID && S_AXI_ARREADY && S_AXI_ARLEN > 4)
f_rd_cvr_valid <= 1;
always @(*)
cover(S_AXI_ARREADY && f_rd_cvr_valid /* && ... */);
//
// Generate cover statements associated with multiple successive bursts
//
// These will be useful for demonstrating the throughput of the core.
//
reg [4:0] f_dbl_rd_count, f_dbl_wr_count;
initial f_dbl_wr_count = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
f_dbl_wr_count = 0;
else if (S_AXI_AWVALID && S_AXI_AWREADY && S_AXI_AWLEN == 3)
begin
if (!(&f_dbl_wr_count))
f_dbl_wr_count <= f_dbl_wr_count + 1;
end
always @(*)
cover(S_AXI_ARESETN && (f_dbl_wr_count > 1)); //!
always @(*)
cover(S_AXI_ARESETN && (f_dbl_wr_count > 3)); //!
always @(*)
cover(S_AXI_ARESETN && (f_dbl_wr_count > 3) && !m_awvalid
&&(!S_AXI_AWVALID && !S_AXI_WVALID && !S_AXI_BVALID)
&& (f_axi_awr_nbursts == 0)
&& (f_axi_wr_pending == 0)); //!!
initial f_dbl_rd_count = 0;
always @(posedge S_AXI_ACLK)
if (!S_AXI_ARESETN)
f_dbl_rd_count = 0;
else if (S_AXI_ARVALID && S_AXI_ARREADY && S_AXI_ARLEN == 3)
begin
if (!(&f_dbl_rd_count))
f_dbl_rd_count <= f_dbl_rd_count + 1;
end
always @(*)
cover(!S_AXI_ARESETN && (f_dbl_rd_count > 3)
/* && ... */
&& !S_AXI_ARVALID && !S_AXI_RVALID);
// }}}
////////////////////////////////////////////////////////////////////////
//
// Assumptions necessary to pass a formal check
//
////////////////////////////////////////////////////////////////////////
//
//
//
// No limiting assumptions at present, check is currently full and
// complete
//
`endif
// }}}
endmodule