dylanmsu / bt656_to_axi4s

VHDL sources for a BT.656 to axi4-stream converter

BT656_2_AXI4S

TODO

• Deinterlace by scanline interpolation in PL
• Upscale for hdmi output (minimum 25MHz pixel clock)

Setup

In my testing i used an FCB-EX1010 analog camera block as video source and connected it to this analog video decoder board i designed . As the FPGA i used the Digilent Zybo Z7-20 development board, but any board with three pmod ports in a row should also work.

Working block diagram

Top level

the clocking wizard is set to 11.36MHz instead of 13.5MHz (27MHZ/2) that is because we want only active pixels in the Internal logic analyzer (ILA). The video signal contains blanking periods which we do not want in our ILA
bt656 clock = 27MHz
blanking period = 272 clks
active pixels/line = 720Y + 720C = 1440 clks
27MHz * (1440/(1440+272))/2 = 11.36MHz

BT656 decoder

Detailed overview

• BT656_0 parses the AV codes from the datastream comming from the BT656 video protocol. It outputs the h-blank, v-blank, active and field signals used by later blocks.

• CbYCrY_UpSampler_0 converts the compressed 4:2:2 (YCb,YCr) encoding to a decompressed 4:4:4 (YCbCr,YCbCr) format.

• YCbCr_2_RGB_0 converts the 4:4:4 YCbCr color space to 4:4:4 RGB

• axis_converter_0 this block servers two purposes. It firstly generates the "end-of-line" and "start-of-frame" signals used by the AXI4-Stream protocol. The second purpose is to align all signals into an actual valid AXI4-Stream.

• axis_data_fifo_0 is a Xilinx IP used to buffer the outgoing video stream.

result

After capturing the AXI4-Stream signals using an ILA in vivado, and decoding the signals using the included python script, this is the result. The image appears to have a low resolution in the y-axis because the camera block i used outputs interlaced video. There is also ghosting present, this may be caused by the non-ideal design of the interface board.

Disclaimer

This is in no way a rigorously tested design and sould NOT be used in an actual implementation. This is a personal project to learn more about VHDL and video processing. I got it to work on my specific setup and i cannot guarantee that it will work on other hardware.