Fast Versatile DMA

Copyright (c) 2019-2022 Antmicro

Overview

FastVDMA is a DMA controller designed with portability and customizability in mind.

Supported features

• Interrupts
• 2D transfers with configurable stride
• External frame synchronization inputs

Supported busses

• Data
  • AXI4
  • AXI-Stream
  • Wishbone
• Control
  • AXI4-Lite
  • Wishbone

Performance

FastVDMA performance was tested in synthetic tests that consisted of transferring an NxM buffer with data where N represents the number of 32-bit words and M represents the number of N word rows to transfer.

FastVDMA was verified in the xc7z030fbg676-2 chip achieving an average throughput of 750MB/s, while being clocked at 250MHz, and average of 330MB/s at 100MHz under the same workload. Both the speeds were performed in a Memory-Stream-Memory configuration using two controllers configured with AXI4 and AXI-Stream buses. The first controller reads data from memory and sends it out via an AXI-Stream interface, while the second receives the stream and writes the data received to a second buffer in memory.

Wishbone and AXI4 busses were connected to a LiteDRAM controller providing access to DDR3 memory. Both busses used a 32-bit data bus to connect to the DDR3 controller.

In both cases the data transferred consisted of a 4MB block of randomly produced data which was subsequently verified for possible transmission errors after each transfer.

Resource usage

The AXI4=>AXI-Stream (MM2S) configuration utilized 425 slices on a xc7z030fbg676-2 chip which was used for tesing the design. AXI-Stream=>AXI4 (S2MM) requires 455 slices on the same chip. Both configurations were instantiated in the same design and connected in a back-to-back configuration that allowed memory-to-memory transfers while still using configurations equipped with AXI-Stream interfaces.

Dependencies

Because the controller is written in Chisel, it requires sbt, scala and java to be installed; additionally the tests require imagemagick.

Simulation

FastVDMA can be simulated as a whole but certain components can be tested separately.

You can simulate the full design by running:

make test

To run all tests, including the full test mentioned above, execute:

make testall

Each testrun generates a .vcd file which can be opened using GTKWave or any other .vcd viewer. Output files are located in a separate subdirectories inside the test_run_dir directory.

The full test should generate an out.png file demonstrating a 2D transfer with configurable stride. The resulting image should look similar to:

Synthesis

To generate a synthesizable verilog file, run:

make verilog

The generated file will be named DMATop$(DMACONFIG).v where DMACONFIG is chosen DMA configuration. Verilog module will be named in the same manner.

Register map

Current register layout is shown in the table below:

For a detailed description of register fields check Register fields.

You can also check WorkerCSRWrapper for more details on how the CSRs are attached to the DMA logic (io.csr(0) refers to 0x00, io.csr(1) to 0x04 and so on).

Customizing FastVDMA

Configuration for the DMA is located in the DMAConfig file. Most of the settings are defined in the DMATop companion object. To change which buses are used you need to set the DMACONFIG environment variable. All possible configurations are listed in the map in DMAConfig file. The DMACONFIG variable consists of names for reader, control and writer buses. For example, to generate a design consisting of AXI Stream reader, AXI4 writer and AXILite control you would need to set DMACONFIG to AXIS_AXIL_AXI. However, if you would like to run already written tests on your specified configuration you will also need to cast buses in io field in DMAFull accordingly to chosen cofiguration. Example:

val io = dut.io.asInstanceOf[Bundle{
                                val control: AXI4Lite
                                val read: AXIStream
                                val write: AXI4
                                val irq: InterruptBundle
                                val sync: SyncBundle}]

You will also need to remeber to choose correct BFMs:

  val axil_master = new AxiLiteMasterBfm(io.control, peek, poke, println)
  val axis_master = new AxiStreamMasterBfm(io.read, width, peek, poke, println)
  val axi4_slave = new Axi4SlaveBfm(io.write, width * height, peek, poke, println)

Source code structure

• src/main/scala/DMAController contains sources of the DMA controller
  • Bus contains definitions of various bus bundles
  • CSR contains code responsible for handling configuration registers
  • Frontend contains modules handling various bus types
  • Worker contains generic code supporting controlling the DMA behaviour
• src/test/scala/DMAController contains tests
  • Bfm contains Bus models that are used in full configuration tests
  • Frontend contains tests used for generating timing diagrams for various bus types
  • Worker contains tests that generate timinig diagrams for the generic part of the DMA

Linux drivers

FastVDMA can be controlled using a Linux driver. The source code and relevant documentation can be found in a separate repository.