high speed LVDS input on low-end boards Zybo/MicroZed/Z-turn

[Daniel_01]

Hi, I'm kind of new to using external I/O connections on FPGA boards but I'm tasked with a project where I plan to interface a high-speed camera with 6 lvds pairs (4 data + 1 clock + 1 sync) with the clock input reaching up to 360 MHz, translating to a max data flow of 720Mbps through each of the 4 data pairs. Although this is the optimal operating condition, I don't necessarily have to achieve such speeds if I can get something close to that using an inexpensive board as low-cost is an important factor here. I was told to look at the following xilinx fpga boards with the Zynq 7000 series chips:

Zybo (~$200): 512 GB DDR3, has VGA and HDMI, only pmod I/O connectors. From what I've read, I understand the high speed pmods are set to 3.3V, but can work at a lower voltage if only used for input, but do I need to physically alter the board for this? What speeds can I actually reach through these connectors?

MicroZed (~$200): 1 GB DDR3, no display out, will have to connect through microheaders on the back, but I can control the I/O bank voltages through the inputs from my carrier card for LVDS. MicroZed manual says "Differential LVDS pairs on a -1 speed grade device are capable of 950Mbps of DDR data" but does this mean the microheader connector is also capable of this rate? I ask this because a similar board from MYiR, the Z-turn (~$100), is very similar in design (but includes HDMI and surprisingly much cheaper) and their support says "Z-turn Board expansion connectors are most for PL ports which can support LVDS differential input, the speed is up to 200MHz in theory." which seems too slow.

From what I've gathered, the Z7010/20 chips and the DDR3 ram are very capable of handling the speeds necessary for operating the camera sensor and the large ram size is important for storing the large number of frames, but I'm confused whether the board these are on allows these chips to receive the input fast enough to make full use of both these chips and the camera sensor. Are there any other low-end boards with large enough memory and fast I/O that can make full use of this camera sensor?

Any help or guidance is much appreciated on where to look and how to design.

Thanks.

[jpeyron]

Hi @Daniel_01,

I have not used the Zybo in this way. Looking at this xilinx forum thread here can take LVDS input. The High speed pmod ports are deferentially paired. We do not have a max frequency metric for the high speed ports. What frequency are you looking to use on the High speed pmod ports? Another potential option is using a board that has an FMC on it like the Zedboard or the Nexys Video with a mezzanine card to facilitate you connection. The FMC has an adjustable voltage,works with LVDS and can communicate a much higher speeds than the high speed pmod ports can.  I would also suggest looking at the Differential PMOD Challenge forum thread as well.

thank you,

Jon

[xc6lx45]

Hi,

On 2/16/2018 at 3:09 AM, Daniel_01 said:

...kind of new to using external I/O connections on FPGA boards

I know nothing about your or your project, so don't get this wrong. But usually, FPGA projects based on board specs are "risky" (and maybe this is a euphemism).
Making it work is one thing, but can you make sure there's a viable route from a "technology" concept demo to a marketable product?

One problem with digital is, the fact that it works means very little. I can't distinguish between one fault in a billion years and one every 1000 hours. The former has sufficient margin. The latter fails miserably at the customer when some dust settles on the board.

Spending a day reading 7-series select IO documentation might be a good plan.

I'd do a quick reality check on the required timing accuracy between LVDS pairs. Sets off a red warning light for me. DRAM interfaces for that speed are routed quite carefully...

If the interface is MIPI D-PHY based, search for that term and "CSI", there are a number of posts on the topic.

[zygot]

@Daniel_01,

Cheap FPGA board and robust LVDS interface seems like facing two opposing criteria that is difficult to meet. I don't have any experience with such a beast.

7 hours ago, xc6lx45 said:

Spending a day reading 7-series select IO documentation might be a good plan.

The preceding advice from xc6lx45 is a good place to start; though a day might not be sufficient for most folks. I realize that taking the time to read documentation and become somewhat knowledgeable about the basics is not how many people approach the platform selection phase which tends to be hurried. I don't know of any good, inexpensive FPGA boards with a well designed LVDS interface connector.  The SYZYGY project offers a possibility at somewhat higher price point through Crowd Supply. I have one on order but I've not gotten notice of shipment for the first batch. The timing of that board probably doesn't help your project.

For a lot more money @jpeyron is correct that the FMC connector offers a number of possibilities for high performance camera interfaces... but now you are in a different league cost wise. The FMC garden is not a playground for the cost conscience. ( Hint, HINT, some forward looking company should do something about this. But so far the one that I've been pushing on keeps saying "who US ?? ... forward thinking ????". )

The closest thing that I know of for a decent camera/FPGA combination at low cost would be from Terasic. Their D8M-GPIO ($100) with their DE0-Nano FPGA board ($90) could work for a project with a limited budget assuming that a camera hasn't been pre-selected. If you have to have a hard ARM dual core their DE0-Nano-SOC ($150) fits the bill. This route means using Intel ( aka Altera ) design tools.

My reading is that you already have a camera in mind so this raises the issue of how you connect the camera connector to the FPGA platform.

If you have a Nexys Video, Genesys2, or Atlys FPGA board one option for camera input is to buy an SDI capable camera and a cheap SDI-HDMI interface and use the HDMI input connector. I've done this with satisfactory results... the caveat being that I don't know the requirements of your video project.

[Daniel_01]

Thanks for your replies. I've discussed my problem with someone more experienced than I am and told me I was wrong to compare the I/O of the cheaper Z-turn with the MicroZed, saying that the MicroZed should be able to handle such speeds (I'm trying to hit 360MHz on the lvds channels) if not close to it, through the MicroHeaders on the back. I also found through the documentation that I can control the voltage of the I/O banks through the MicroHeaders as well which is nice. Since there's no guarantee I can achieve such speeds with the Zybo pmods, it might not be worth trying given time constraints.

I will continue to investigate further and read more documentation as suggested, but I plan to give the MicroZed a try and see what I can achieve with it and will probably report back if I managed to get something working.

Thanks again.