AXI4-Stream

What is this repository for?

The IObundle AXISTREAM is a RISC-V-based Peripheral written in Verilog, which users can download for free, modify, simulate, and implement in FPGA or ASIC. This peripheral provides an AXI4-Stream interface for communication with external systems. It also provides a Direct Memory Access (DMA) interface using another AXI4-Stream interface.

This peripheral can be used as a verification tool of the OpenCryptoTester project.

This repository contains both the AXISTREAM_IN and AXISTREAM_OUT peripherals. The configuration and sources for these peripherals are located within the axistream_in and axistream_out folders, respectively.

Integrate in SoC

• Check out IOb-SoC-SUT

Usage

The main classes that describe these cores are located in the iob_axistream_in.py and iob_axistream_out.py Python modules. They contain a set of methods useful to set up and instantiate these cores.

The following steps describe the process of creating an AXISTREAMIN peripheral in an IOb-SoC-based system (the steps for the AXISTREAMOUT peripheral are similar):

1. Import the iob_axistream_in class
2. Run the iob_axistream_in.setup() method to copy the required sources of this module to the build directory.
3. Run the iob_axistream_in(...) method to create a Verilog instance of the AXISTREAMIN peripheral.
4. Use this core as a peripheral of an IOb-SoC-based system:
   1. Add the created instance to the peripherals list of the IOb-SoC-based system.
   2. Write the firmware to run in the system, including the iob-axistream-in.h C header and use its driver functions to control this core.

Example configuration

The iob_soc_sut.py script of the IOb-SoC-SUT system, uses the following lines of code to instantiate an AXISTREAMIN peripheral with the instance name AXISTREAMIN0:

# Import the iob_axistream_in class
from iob_axistream_in import iob_axistream_in

# Class of the SUT system
class iob_soc_sut(iob_soc):
  ...
  # Method that runs the setup process of the SUT system
  @classmethod
  def _post_setup(cls):
    ...
    # Setup the AXISTREAMIN module (Copies every file and dependency required to the build directory)
    iob_axistream_in.setup()
    ...
    # Create a Verilog instance of this module, named 'AXISTREAMIN0', and add it to the peripherals list of the system.
    cls.peripherals.append(
        iob_axistream_in(
            "AXISTREAMIN0", # Verilog instance name
            "SUT AXI input stream interface", # Instance description

            # Verilog parameters to pass to this instance.
            # In this example, we use a 32-bit TDATA signal.
            parameters={"TDATA_W": "32"},
        )
    )

Direct Memory Access (DMA)

This peripheral provides a DMA interface using AXI4-Stream. Is also contains the fifo_threshold port to be used as an interrupt for the CPU. This signal can be used to trigger data transfers via DMA.

• Check out IOb-DMA for more details.

The iob_soc_tester.py script of the IOb-SoC-SUT system, provides examples of AXISTREAM peripherals configured to use the DMA interface.

Brief description of C interface

The AXISTREAM cores store the values in an internal FIFO buffer, which can be accessed via software.

An example of some C code is given, with explanations:

For the AXISTREAMIN peripheral:

//Set AXISTREAMIN base address
axistream_in_init(int base_address);

//Get a 32-bit word from FIFO
uint32_t received_word = axistream_in_pop_word();

//Signal when FIFO empty
bool is_empty = axistream_in_empty();

//Returns if the last value of read from FIFO was the end of frame (by TLAST signal) and gets rstrb from that value
bool was_last = axistream_in_was_last(char *rstrb);

//Pulse soft reset
axistream_in_reset();

//Enable peripheral
axistream_in_enable();

//Disable the tready signal, preventing new transfers
axistream_in_disable();

//Get value from FIFO [can be used instead of axistream_in_pop_word() and axistream_in_was_last()]
//Returns true if this word was tlast, false otherwise
//Arguments:
//    byte_array: byte array to be filled with 4 bytes popped from FIFO word
//    n_valid_bytes: Number of valid bytes in this word (will always be 4 if tlast is not active)
bool is_last = axistream_in_pop(uint8_t *byte_array, uint8_t *n_valid_bytes);

//Set the FIFO threshold level
//If the FIFO level is equal or higher than the threshold, trigger an interrupt
axistream_in_set_fifo_threshold(uint32_t threshold);

//Get current FIFO level
uint32_t fifo_level = axistream_in_fifo_level();

For the AXISTREAMOUT peripheral:

//Set AXISTREAMOUT base address
//If the instance has tdata_w > 1 byte, don't use this function to initialize it. Use function: axistream_out_init_tdata_w()
axistream_out_init(int base_address);

//Set AXISTREAMOUT base address and tdata width
axistream_out_init_tdata_w(int base_address, int tdata_w);

//Free memory from initialized instances
axistream_out_free();

//Place value in FIFO, also place wstrb for a word with TLAST signal.
//If tlast_wstrb is zero then all bytes are valid and don't send TLAST signal
//tlast_wstrb has 1 up to 4 bits depending on the output width of the FIFO (width of TDATA signal). 
//If TDATA has 8 bits, then tlast_wstrb has 4 bits (1 for each valid byte of the last 32bit word in FIFO);
//If TDATA has 16 bits, then tlast_wstrb has 2 bits (1 for each valid 16-bit word of the last 32bit word in FIFO);
//If TDATA has 32 bits, then tlast_wstrb has 1 bit (in this case, 32 bits are always valid independently of tlast_wstrb, this bit only selects if we send TLAST signal)
axistream_out_push_word(uint32_t value, char tlast_wstrb);

//Place value in FIFO, also place wstrb for a word with TLAST signal. [can be used instead of axistream_out_push_word()]
//Arguments:
//    byte_array: bytes to insert in fifo
//    n_valid_bytes: number of valid bytes in value, should be multiple of tdata_w
//    is_tlast: if value contains tlast
axistream_out_push(uint8_t *byte_array, uint8_t n_valid_bytes, bool is_tlast);

//Signal when FIFO is full
bool full = axistream_out_full();

//pulse soft reset
axistream_out_reset();

//Enable peripheral
axistream_out_enable();

//Disable peripheral, preventing new transfers
axistream_out_disable();

//Set the FIFO threshold level
//If the FIFO level is equal or lower than the threshold, trigger an interrupt
axistream_out_set_fifo_threshold(uint32_t threshold);

//Get current FIFO level
uint32_t fifo_level = axistream_out_fifo_level();

Acknowledgement

The OpenCryptoTester project is funded through the NGI Assure Fund, a fund established by NLnet with financial support from the European Commission's Next Generation Internet programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 957073.