Follow Up to the 7 Ways to Leave Your Spartan-6 Program: How Well Do You Like Working with the Spartan-7 FPGA?

I am a person without any experience in hardware design. I work as a JAVA software developer for banking applications with some foray into embedded software development for payment terminals and vending machines.

It has been my first in-depth experience with an FPGA, so I cannot compare it with other FPGAs or with other development environments such as Intel Quartus which, although I know of, I have only used it to run examples without any modification.

Earlier this year I participated in the 2021 Adaptive Computing Challenge Developer Contest on Hasckster.io in the category of Edge Computing with Xilinx Kria KV260 Vision Starter Kit. It was a different experience because that kit did not require any FPGA knowledge. Xilinx provides a complete environment for someone with only knowledge of embedded software to build applications that can take advantage of hardware accelerators for machine learning and computer vision with a wide variety of pre-trained models.

The 7 Ways to Leave Your Spartan-6 Program has been a totally different experience. I started from the total ignorance of what an FPGA was and I have ended up understanding well what an FPGA is, what the Spartan-7 contributes and daring with a new Spartan challenge in the new Sensor Fusion Challenge with the SP701 development board.

What has cost me the most? Understand what the development tools are and what is the function of each one. For a person outside the world of Xilinx, my first problem was to understand what it means, Vivado, Vitis, Vitis HLS, ISE, SDK, Simulink Matlab, Petalinux, ... It is a real nonsense for someone who is starting out. The Xilinx development tools have changed their names and functions over time and it is very difficult to make a mental map of what each one does, what FPGAs they support and what development environment (operating system, processor, RAM memory, disk memory) require. A simple document presenting the different development suites for Xilinx FPGAs over time with the requirements for each would make it easier for those wanting to get started on their own to get started.

The Spartan-7 has been fascinating to me, perhaps more because of the ease of working with Vivado and Vitis and Vitis HLS. I barely remember any problem. In just a few months I have been able to make my own PL designs in SystemVerilog, Custom IP Peripherals, baremetal applications with Microblaze and High Level Synthesis with Vitis HLS or simply build systems with Vivado IP Integrators and the block designer.

The documentation is very complex and extensive. There is so much that it is sometimes difficult to try to do a quick read without getting lost in another document along the way. The hardest part for me has been getting into the concept of "Vitis unified software platform" to understand which libraries can be used directly with the Spartan-7.

I still have a lot to explore about the Spartan-7 and I'm taking advantage of the Sensor Fusion challenge to improve my knowledge.

Summing up the program has been a unique experience for me, I have learned a lot in a very short time. I would repeat the participation in a similar program. Having 24 other program partners has also been very satisfying. And I would also like to thank many element14 members from outside the program for their participation in the forums, who helped me when I had a blockage with the Digilent Arty S-50 board hardware. Finally, thanks to the element14 team who gave me and others an immediate response when we had a problem with the program that did not allow us to go at the pace we wanted.

Before enrolling in the "7 Ways to Leave Your Spartan-6 Program", I had few years of experience working (on an off) with Xilinx's Zynq-7000 FPGAs. For those unfamiliar with Zynq series, these FPGAs have built-in hard processors in addition to the usual configurable FPGA fabric. With regards to working with Spartan-7, following are some points worth mentioning, in no particular order:
- I am not a core HDL person, so I've always found Vivado/Vitis/HLS very useful. This thing continued with the Spartan-7 as I was already quite familiar with the toolchain. At work I have had to deal with some Spartan (3/6) designs in the past few years and going back to the decade old ISE has always been a turn-off. Not the case when using Spartan-7. And Vivado/Vitis gets frequent updates that you can use without buying licenses. Big plus for me.
- A lot of the openly available IPs, for example from Digilent, are compiled for Zynq-7000. After going through the IP source codes (HDMI), I found that they actually didn't use anything specific to the Zynq-7000 and I was able to recompile them for Spartan-7 using the IP integrator and use them in my designs. However, I do wish the original authors (Digilent in this case) had compiled them for Spartan-7 to begin with. It would save people some time.
- The main issue I encountered with the Spartan-7 had to do with the use of Microblaze. It took me a few days and some asking around on the element14 forum to get the very basic design to work. The technical reasons aside, I do think that the process should have been much smoother. If I want to add a Microblaze to my design, Vivado should help do those things correctly without me having to make connections in particular ways manually. A user should be able to do this much without reading the documentation. Maybe I am just spoilt by how easy it is to run a basic processor design with the Zynq series.
- I like the idea of being able to use an ARM processor within the device. However, the major turn-off for me has always been the fact that I cannot use Vitis (SDK) to write the code for it and have to install yet another software for it. It would be nicer if I can just use the same familiar Vitis SDK to program the soft-ARM cores as well.
- The disk space consumption of the Xilinx tools has always been a pain point. It's more than any other software that I use by a good margin. I hope this gets improved in future.

I might be a little late in my feedback since nowadays I am a little busy. But I would like to say that overall it was a really good experience in working on the Spartan 7 FPGA board. This was the first time I worked on a FPGA board. I would just like to point out some things that I as a beginner struggled for:
1. I found it very hard to understand the online documentation and tutorials available. It was only because of the road test blogs posted on E14, I was able to start working on the board.
2. I couldn't find much material on Vivado HLS (that I could understand easily).

3. I think there should be some short video tutorials on basic projects. After going through such basic tutorials, understanding the complete documentation becomes easier.
4. It was taking around an hour to synthesize the simplest designs on the board consisting of the MicroBlaze IP. But around a week before the deadline, it became suddenly faster, it started synthesizing in around 15 minutes. Now, I don't know what happened back then, had I changed some setting by mistake, some driver issue or it was something else but that wasted a lot of time.