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Eclypse Z7 vs. Artix-7 and Timing Jitter


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I am not familiar with FPGA SoC development. I need to develop a real-time RF signal processor that takes in two RF signals (I and Q), does some processing, and outputs another RF signal via a DAC. It seems the Eclypse Z7 with ADC and DAC Zmods could be ideal for my purpose. However, I do not need the integrated ARM processor. In fact, I do not want the ARM processor involved at all because my application requires very precise timing.

Is it possible to use the Zynq-7000 in the Eclypse Z7 without the processor in the loop, whatsoever, just like an Artix-7? I can't afford any bottlenecks or timing jitter caused by having to pipe data through the CPU.

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On 2/8/2021 at 7:28 PM, zygot said:

Have you looked at the XEM-7320? I've used it with both ZMODs.

Thanks, that is an interesting option. However, I don't see any external reference clock inputs. It just mentions a 200 MHz on board oscillator.

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On 2/8/2021 at 7:28 PM, zygot said:

Have you looked at the XEM-7320? I've used it with both ZMODs.

I looked into the XEM-7320 from Opal Kelly. It is interesting, but I found almost no real documentation. All that I could find is pinouts, PCB design files and a link to their FrontPanel SDK for communication between the board and the host PC. There wasn't even an example of wiring up a single switch, LED and NOT gate to flash an LED. No mention of Xilinx Vivado, board support files or getting started. I did notice that they generously offer paid tech support. Am I missing something or are there no real examples and documentation provided?

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Well, you are correct that the Opal Kelly boards don't have an SMT clock in or clock out port. Also, Opal Kelly doesn't provide schematics. Normally, for me this would be a non-starter, but I've had enough past experience with their stuff to know that I can generally get to where I want to with a bit of effort. Once you buy a board you can install their FrontPanel software that includes source for their demos. You won't find any Signal Processing demos but you will find enough to use the meager resources that the boards provide... in the case of the XEM7320 this is DDR, and a USB 3.1 superspeed interface. The SYZYGY support isn't very good. Neither is Digilent's support for their ZMODs. That's just the way it is. If you find better options then please post your success here for everyone to read about.

One option is to head over to a conversion device vendor and see what kind of FPGA support they offer and what boards their demos work on. At the moment that is Analog Devices. Beware that even with good support there is a lot you have to know about to determine if what you are buying is what you need for your particular project.

You should know that for most Signal Processing applications just having an external clock input isn't sufficient. In my experience the analog front end design before the ADC and the analog post DAC processing is highly application dependent and vital to good results. Companies that I'm familiar with don't buy general purpose off the shelf hardware for this reason and design their own application specific hardware. There no digital signal processing without the analog signal processing. You have to accommodate all requirements through the entire signal chain.

Your mention of using an LED reminded me that Opal Kelly doesn't even provide enough information ( that I could find anyway ) to know if lighting an LED requires a high or low signal. It turns out that to turn off an LED you need a 'Z'... I haven't run into an FPGA vendor that doesn't make me scratch my head and say " what are they thinking?". Being irritated is part of the FPGA experience.

In case it's not obvious by now, I don't work for Digilent or get any compensation for my posts to their web sites.

[edit] All SYZYGY ports have clock-in and clock-out connectivity.  Of course, if your conversion interface pod doesn't have a suitable input clock connector then wasting a whole port just to get a clock is painful. There's always an alternative when no off the shelf hardware exists. You can design your own ADC/DAC add-on board to fit your needs. Both SYZYGY and FMC connectors are good for this though the high-speed connectors aren't trivial to work with using free PCB layout software. You best bet is likely KiCAD.

 

Edited by zygot
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FPGA support for extending applications into the analog domain have never been competently address by the FPGA vendors or their close partners, particularly at the low end of the $$$$ budget. Terasic has been the exception. For applications that are below an Fs of 100 KHz you can find hardware to do simple experiments... unless you have very specific clocking requirements. If all you want to do is develop your HDL signal processing skill then you can find enough cheap hardware to get started. If you have specific requirements and specifications then you need a hardware platform that has been specifically designed to meet those specifications. At least there are some options. Digilent has cheap ADC and DAC PMODs for general purpose experimentation. And that doesn't imply trivial algorithmic implementations.

It would be nice if the FPGA board vendors got some input as to what basic requirements are for designing a usable platform before they go to the trouble of designing and selling products. Nothing seems to stand in the way of success more than EGO. But imagining that you know what you are doing and actually knowing what you are doing are two different animals.

 

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Look at the Terasic THDB_ADA_HSMC plus the MAX10 Development Kit. For under $500 you can have 2 ADC and 2 DAC channels suitable for Fs in the 100 Mhz range plus SMA connectors for external clocks for both ADC and DAC sampling. For PC connectivity there's an Ethernet  PHY. There's also external memory capable of sample buffering. In fact this combination makes a good adc/dac server for my Digilent FPGA platforms. You will have to know how to do proper HDL FPGA design and development though as there aren't beginner's demo project putting it all together.



Given recent product announcements I suspect ( I don't have any direct information supporting ) that Digilent has a conflict in providing a really good affordable Signal Processing platform because it would interfere with sales of other products on the horizon. They could make a nice FMC mezzanine board for the Genesys2 with SYZYGY ports or better yet a Genesys2 with SYZYGY ports instead of the FMC connector. Connectors for external clock inputs is an essential component as is access to a programmable clock module.  Designing such a platform is well within their abilities and means. It just has to fit within their marketing strategy. From reading posts to this site over the years I have no doubt about the need for such a platform. Who want's to fill it?



While having those ARM/NEON cores might be useful, no FPGA with ARM that I know of has a really good hose between the core complex and the FPGA logic; you are stuck with AXI. Worse yet there are few platforms based on a SOC-FPGA that have separate external memory connected to both the ARM complex and the logic. For a really good platform the logic has to have direct connectivity to external memory. Finally, for a general purpose platform easy high speed connectivity to a PC is desirable. I wouldn't add  much cost to provide a decent USB 3.0 solution to that. This has been around for years. It sure would be nice of new hardware kept up with the capabilities of the FPGA devices they are selling. For a number of FPGA development projects the ARM cores embedded in the FPGA device just get in the way of a good project design.

[edit] The cheaper Terasic ADA boards only support 65 MHz ADC and 125 MHz DACs AC sampling. The more expensive DDC support 150 MHz ADC and 250 MHz DAC Fs rates. The ADA board has a GPIO version and an HSMC version. The C5P + ADA_GPIO makes for an interesting platform. The more expensive Cyclone VGT board + DDC is an even more interesting platform. Xilinx support for such projects is far behind Intel's for students and customers on a budget. So far they seem to be immune to embarrassment but I do what I can. Perhaps you'll see a post about how to create an appliance that let's your PC do Signal Processing applications in the near future.


There's a lot of things to carefully consider when choosing hardware for this kind of project. Be careful and do your homework to avoid regret...

One very positive development in this arena is the embrace by Digilent of SYZYGY and the release of 2 very good converter pods. These are the best at what they do that I've run into, and I'm always looking for such products. Now if only Digilent could figure out how do design and support an FPGA platform that let users take advantage of those wonderful ZMODs. I'm hoping to see a mixed ADC/DAC pod at some time. 

Edited by zygot
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