AXI stream interfaces in Xilinx system generator IP

Question

I have an example design in system generator for image processing which has one input image and one output image. I would like to send data through AXI stream interface and export it as an IP core to Vivado IP integrator and develop the design further using DMA and software in SDK.

Firstly is it possible to have AXI stream interface in my design? If yes, how can I implement it? Can anybody help me?

Thanks in advance. (i have attached image of the example here) Image_filter

Answer 1

I am currently working on a very similar project, (I am not using System Generator though), so I bet I could give you some pointers. As far as I remember SysGen can produce some VHDL or Verilog code of your design. So:

After you get the HDL code of your design, pack it as a new IP in Vivado. There are plenty of tutorials on how to do this, it should be easy with a little search. You should wisely choose the interfaces you want to implement. You're going to definitely need an AXI Stream Slave interface for accepting the incoming data and an AXI Stream Master interface to transmit the results.

After you package your IP, you can begin building your system block-by-block (there are also some good tutorials on this, see end of answer). You will need to use the AXI DMA IP (or the Video DMA, depending on your needs) and you'll have to configure it properly, like choosing register-mode or scatter-gather, channels, etc.

Be extremely careful to generate the proper AXI synchronization signals correctly, as they can totally ruin your design (and nerves). It's easy but it requires some study of the AXI documentation provided by Xilinx (ARM's docs are too complicated for my taste).

Finally, you will definitely find very useful information on the following resources:

1. Xilinx Forum

2. FPGAdeveloper's example

3. another AXI-stream based design example

4. FPGA note wiki

5. AXI DMA Product Guide

6. Channel of Dr. Sadri of TU Kaiserslautern, really helpful to deeply understand AXI design concepts

Good luck!

PS: Simulators are your friends! Never try implementing your freshly written code directly onto the system design. Modelsim can save you significant time and effort which would otherwise be spent on pointless debugging.

Answer 2

Firstly is it possible to have AXI stream interface in my design?

Yes, it is.

If yes, how can I implement it? Can anybody help me?

I have a similar project develop in Vivado 2015.3: an image filter (created with "High Level Synthesis") and this design block:

The High Level Synthesis code should look like:

#include "top.h"

void hls_sobel(
    hls::stream< ap_axiu<8,1,1,1> > &video_in,
    hls::stream< ap_axiu<8,1,1,1> > &video_out
            )
{
ap_uint<16> Image_w=IMAGE_W_MAX;
ap_uint<16> Image_h=IMAGE_H_MAX;
// Create AXI streaming interfaces for the core
#pragma HLS INTERFACE axis port=video_in  bundle=video_in
#pragma HLS INTERFACE axis port=video_out bundle=video_out

// No control interface - auto-start as soon as there's an input frame
#pragma HLS INTERFACE ap_ctrl_none port=return  // no handshakes

hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> mat_in(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> mat_out(Image_h, Image_w);

hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> inx(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> iny(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_16SC1> sobelx(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_16SC1> sobely(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_16SC1> zerox(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_16SC1> zeroy(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> absx(Image_h, Image_w);
hls::Mat<IMAGE_H_MAX, IMAGE_W_MAX, HLS_8UC1> absy(Image_h, Image_w);

#pragma HLS dataflow
// read input and convert from axi-stream to Mat
hls::AXIvideo2Mat(video_in, mat_in);

// calculate Sobel in X and Y directions
hls::Duplicate(mat_in, inx, iny);
hls::Sobel<1,0,3>(inx, sobelx);
hls::Sobel<0,1,3>(iny, sobely);
// calculate abs of said Sobel
hls::Zero(zerox);
hls::Zero(zeroy);
hls::AbsDiff(sobelx, zerox, absx);
hls::AbsDiff(sobely, zeroy, absy);
// add both abs
hls::AddWeighted(absx, 1, absy, 1, 0, mat_out);

// write output
hls::Mat2AXIvideo(mat_out, video_out);

}

As you can note, a DMA is used. For the Video-Image application, I recommend using a Video-DMA (VDMA) to send all the pixel information via streaming-interface. After, in the SDK, it is easy to manage the transfer using the function in the Board Support Package (BSP).

Also, you can note that in the code above is explicitly specified hls::stream< ap_axiu<8,1,1,1> > &video_in,! In this way, I am creating a streaming interface.

Here you can find a tutorial about HLS image processing filter. In the last page, there are useful links. Follow them to realize the same system of the example.

I hope this can help

Answer 3

If I understand correctly, you want to know how to create an AXI Stream interface inside your system generator design.

Yes it is possible to do it. You should have atleast two inputs in your design with names, for example, image_tdata and image_tvalid (gateway in). When you generate IP core, sysgen will recoginize this as an AXI STREAM. The format is important. It must be "$customname_tdata" and "$customname_tvalid". You can add other inputs as well to add to the AXI STREAM such as "$customname_tlast", "$customname_tready".