Verilog AXI Stream Components Readme

For more information and updates: http://alexforencich.com/wiki/en/verilog/axis/start

GitHub repository: https://github.com/alexforencich/verilog-axis

Introduction

Collection of AXI Stream bus components. Most components are fully parametrizable in interface widths. Includes full cocotb testbenches that utilize cocotbext-axi.

Documentation

arbiter module

General-purpose parametrizable arbiter. Supports priority and round-robin arbitration. Supports blocking until request release or acknowledge.

axis_adapter module

The axis_adapter module bridges AXI stream buses of differing widths. The module is parametrizable, but there are certain restrictions. First, the bus word widths must be identical (e.g. one 8-bit lane and eight 8-bit lanes, but not one 16-bit lane and one 32-bit lane). Second, the bus widths must be related by an integer multiple (e.g. 2 words and 6 words, but not 4 words and 6 words). Wait states will be inserted on the wider bus side when necessary.

axis_arb_mux module

Frame-aware AXI stream arbitrated multiplexer with parametrizable data width and port count. Supports priority and round-robin arbitration.

Wrappers can generated with axis_arb_mux_wrap.py.

axis_async_fifo module

Configurable word-based or frame-based asynchronous FIFO with parametrizable data width, depth, type, and bad frame detection. Supports power of two depths only.

axis_async_fifo_adapter module

Configurable word-based or frame-based asynchronous FIFO with parametrizable data width, depth, type, and bad frame detection. Supports different input and output data widths, inserting an axis_adapter instance appropriately. Supports power of two depths only.

axis_broadcast module

AXI stream broadcaster. Duplicates one input stream across multiple output streams.

axis_cobs_decode

Consistent Overhead Byte Stuffing (COBS) decoder. Fixed 8 bit width.

axis_cobs_encode

Consistent Overhead Byte Stuffing (COBS) encoder. Fixed 8 bit width. Configurable zero insertion.

axis_crosspoint module

Basic crosspoint switch. tready signal not supported. Parametrizable data width.

Wrappers can generated with axis_crosspoint_wrap.py.

axis_demux module

Frame-aware AXI stream demultiplexer with parametrizable data width and port count.

axis_fifo module

Configurable word-based or frame-based synchronous FIFO with parametrizable data width, depth, type, and bad frame detection. Supports power of two depths only.

axis_fifo_adapter module

Configurable word-based or frame-based synchronous FIFO with parametrizable data width, depth, type, and bad frame detection. Supports different input and output data widths, inserting an axis_adapter instance appropriately. Supports power of two depths only.

axis_frame_join module

Frame joiner with optional tag and parametrizable port count. 8 bit data path only.

Wrappers can generated with axis_frame_join_wrap.py.

axis_frame_length_adjust module

Frame length adjuster module. Truncates or pads frames as necessary to meet the specified minimum and maximum length. Reports the original and current lengths as well as whether the packet was truncated or padded. Length limits are configurable at run time.

axis_frame_length_adjust_fifo module

Frame length adjuster module with FIFO. Truncates or pads frames as necessary to meet the specified minimum and maximum length. Reports the original and current lengths as well as whether the packet was truncated or padded. FIFOs are used so that the status information can be read before the packet itself. Length limits are configurable at run time.

axis_ll_bridge module

AXI stream to LocalLink bridge.

axis_mux module

Frame-aware AXI stream multiplexer with parametrizable data width and port count.

Wrappers can generated with axis_mux_wrap.py.

axis_pipeline_fifo module

Parametrizable register pipeline with output FIFO. LENGTH parameter determines number of register stages. For a sufficient pipeline length and bus width, consumes fewer resources than axis_pipeline_register while providing full throughput.

axis_pipeline_register module

Parametrizable register pipeline. LENGTH parameter determines number of register stages (instances of axis_register).

axis_ram_switch module

Frame-aware AXI stream RAM switch with parametrizable data width, port count, and FIFO size. Uses block RAM for storing packets in transit, time-sharing the RAM interface between ports. Functionally equivalent to a combination of per-port frame FIFOs and width converters connected to an AXI stream switch.

axis_rate_limit module

Fractional rate limiter, supports word and frame modes. Inserts wait states to limit data rate to specified ratio. Frame mode inserts wait states at end of frames, word mode ignores frames and inserts wait states at any point. Parametrizable data width. Rate and mode are configurable at run time.

axis_register module

Datapath register with parameter to select between skid buffer, simple buffer, and bypass. Use to improve timing for long routes. Use REG_TYPE parameter to select the type of register (bypass, simple, or skid buffer).

axis_srl_fifo module

SRL-based FIFO. Good for small FIFOs. SRLs on Xilinx FPGAs have a very fast input setup time, so this module can be used to aid in timing closure.

axis_srl_register module

SRL-based register. SRLs on Xilinx FPGAs have a very fast input setup time, so this module can be used to aid in timing closure.

axis_stat_counter module

Statistics counter module. Counts bytes and frames passing through monitored AXI stream interface. Trigger signal used to reset and dump counts out of AXI interface, along with tag value. Use with axis_frame_join to form a single monolithic frame from multiple monitored points with the same trigger.

axis_switch module

Frame-aware AXI stream switch with parametrizable data width and port count.

Wrappers can generated with axis_switch_wrap.py.

axis_tap module

AXI stream tap module. Used to make a copy of an AXI stream bus without affecting the bus. Back-pressure on the output results in truncated frames with tuser set.

ll_axis_bridge module

LocalLink to AXI stream bridge.

priority_encoder module

Parametrizable priority encoder.

Common signals

tdata   : Data (width generally DATA_WIDTH)
tkeep   : Data word valid (width generally KEEP_WIDTH)
tvalid  : Data valid
tready  : Sink ready
tlast   : End-of-frame
tid     : Identifier tag (width generally ID_WIDTH)
tdest   : Destination tag (width generally DEST_WIDTH)
tuser   : User sideband signals (width generally USER_WIDTH)

Common parameters

DATA_WIDTH           : width of tdata signal
KEEP_ENABLE          : enable tkeep signal (default DATA_WIDTH>8)
KEEP_WIDTH           : width of tkeep signal (default (DATA_WIDTH+7)/8)
LAST_ENABLE          : enable tlast signal
ID_ENABLE            : enable tid signal
ID_WIDTH             : width of tid signal
DEST_ENABLE          : enable tdest signal
DEST_WIDTH           : width of tdest signal
USER_ENABLE          : enable tuser signal
USER_WIDTH           : width of tuser signal
USER_BAD_FRAME_VALUE : value of tuser indicating bad frame
USER_BAD_FRAME_MASK  : bitmask for tuser bad frame indication

Source Files

arbiter.v                          : General-purpose parametrizable arbiter
axis_adapter.v                     : Parametrizable bus width adapter
axis_arb_mux.v                     : Parametrizable arbitrated multiplexer
axis_async_fifo.v                  : Parametrizable asynchronous FIFO
axis_async_fifo_adapter.v          : FIFO/width adapter wrapper
axis_broadcast.v                   : AXI stream broadcaster
axis_cobs_decode.v                 : COBS decoder
axis_cobs_encode.v                 : COBS encoder
axis_crosspoint.v                  : Parametrizable crosspoint switch
axis_demux.v                       : Parametrizable demultiplexer
axis_fifo.v                        : Parametrizable synchronous FIFO
axis_fifo_adapter.v                : FIFO/width adapter wrapper
axis_frame_join.v                  : Parametrizable frame joiner
axis_frame_length_adjust.v         : Frame length adjuster
axis_frame_length_adjust_fifo.v    : Frame length adjuster with FIFO
axis_ll_bridge.v                   : AXI stream to LocalLink bridge
axis_mux.v                         : Multiplexer generator
axis_pipeline_fifo.v               : AXI stream register pipeline with FIFO
axis_pipeline_register.v           : AXI stream register pipeline
axis_ram_switch.v                  : AXI stream RAM switch
axis_rate_limit.v                  : Fractional rate limiter
axis_register.v                    : AXI Stream register
axis_srl_fifo.v                    : SRL-based FIFO
axis_srl_register.v                : SRL-based register
axis_switch.v                      : Parametrizable AXI stream switch
axis_stat_counter.v                : Statistics counter
axis_tap.v                         : AXI stream tap
ll_axis_bridge.v                   : LocalLink to AXI stream bridge
priority_encoder.v                 : Parametrizable priority encoder

AXI Stream Interface Example

two byte transfer with sink pause after each byte

          __    __    __    __    __    __    __    __    __
clk    __/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__
                _____ _________________
tdata  XXXXXXXXX_D0__X_D1______________XXXXXXXXXXXXXXXXXXXXXXXX
                _____ _________________
tkeep  XXXXXXXXX_K0__X_K1______________XXXXXXXXXXXXXXXXXXXXXXXX
                _______________________
tvalid ________/                       \_______________________
       ______________             _____             ___________
tready               \___________/     \___________/
                      _________________
tlast  ______________/                 \_______________________

tuser  ________________________________________________________

two back-to-back packets, no pauses

          __    __    __    __    __    __    __    __    __
clk    __/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__
                _____ _____ _____ _____ _____ _____
tdata  XXXXXXXXX_A0__X_A1__X_A2__X_B0__X_B1__X_B2__XXXXXXXXXXXX
                _____ _____ _____ _____ _____ _____
tkeep  XXXXXXXXX_K0__X_K1__X_K2__X_K0__X_K1__X_K2__XXXXXXXXXXXX
                ___________________________________
tvalid ________/                                   \___________
       ________________________________________________________
tready
                            _____             _____
tlast  ____________________/     \___________/     \___________

tuser  ________________________________________________________

bad frame

          __    __    __    __    __    __
clk    __/  \__/  \__/  \__/  \__/  \__/  \__
                _____ _____ _____
tdata  XXXXXXXXX_A0__X_A1__X_A2__XXXXXXXXXXXX
                _____ _____ _____
tkeep  XXXXXXXXX_K0__X_K1__X_K2__XXXXXXXXXXXX
                _________________
tvalid ________/                 \___________
       ______________________________________
tready
                            _____
tlast  ____________________/     \___________
                            _____
tuser  ____________________/     \___________

Testing

Running the included testbenches requires cocotb, cocotbext-axi, and Icarus Verilog. The testbenches can be run with pytest directly (requires cocotb-test), pytest via tox, or via cocotb makefiles.