I really don't know where to put this so I decided to ask myself a question and then propose an answer. Perhaps there needs to be a new home for basic assistance for users.
A frequent question for beginners and even experienced people resolves around how to select an FPGA development board. The answer depends on what you want to do with it. The analysis can be anywhere from simple to complex. But there are three issues to resolve that will simplify the process of making a selection.
Three questions that only you can answer are:
What do you want to do with the hardware ?
What is your budget ?
What is your experience level ?
For our context I'll be ignoring a 4th question, which might be the real driver for your interest. That question is: "What are your goals?". If you are just curious then that's different than if you want to add marketable skills to your resume. Also, you might perceive knowing how to develop with a particular device, such as Zynq, as an over-arching motivation. My view is that the Zynq is a great solution for a number of problems for a competent FPGA developer but except for running Ubuntu almost anything
that I can do in software can be done with logic resources in an FPGA. On the theory that goals tend to change with experience and knowledge I'm going to proceed without answering that question.
So let's group some possible answers to the responses to the previously listed questions and provide a bit of guidance.
Case 1:
1) $0 OR
2) either "I don't know" or "I just want to learn how to use an FPGA". OR
3) None
If you don't have a specific hardware project requiring an FPGA you don't need to spend anything to learn or develop FPGA applications and I suggest that you don't. Just get the latest version of Vivado or ISE. You can do everything except spend time debugging hardware with nothing more than Vivado or ISE. If you have no experience with VHDL or Verilog then I strongly suggest buying a used textbook but this is not a requirement. Xilinx provides information about how to use its devices and tools but assumes that you know enough about an HDL to accomplish synthesis or simulation for a project. Learning an HDL in the context of a directed or group setting is easier than teaching yourself, but not necessary. FPGA devices are complex and the tools are complex and no one is going to spend a Saturday afternoon reading the Xilinx literature and being a competent FPGA developer by Sunday. Understand that FPGA development is really just digital logic development. So if you come from a software background you might have to re-wire your brain a bit to grasp the basic concepts. Learn the basic concepts, how to be fluent in an HDL for both synthesis and simulation and how to know how to simulate effectively. You simply can't do competent FPGA development unless you know how to write a testbench in your HDL and perform effective simulation.
You don't need to read the vendor manuals for the resources in any particular FPGA device but having an understanding of what and FPGA is certainly can't hurt.
Case 2:
1) "not much" AND
2) "Nothing in particular but simple logic designs" AND
3) I'm competent using an HDL, simulator tools, and Vivado or ISE
If these are your answers then the advice for case 1 might still be valid. It's true that most of us need some form of positive feedback to motivate us to do hard work. An FPGA development board might just do the trick. So my advice is simple. Spend the least amount possible. There are decent boards with a JTAG programming and minimal interface resources available such as the CMOD or DE0-NANO for < $100. Aside from the motivation factor you still don't need hardware to accomplish even complicated designs so why spend money until you know what to spend you money on? If you are determined to spend your allowance then start off with the least expensive and least expensive to replace board. The buttons, LEDs and switches can all be simulated. For basic HDL designs you can use global clock buffers and not worry about anything except pin location constraints.
Case 3:
1) "not much" AND
2) "I want to use and FPGA to build a variety of hardware prototypes that don't require using advanced FPGA IO features" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably competent designing with digital, analog or mixed-signal devices."
For this case there are a number of inexpensive modules that offer 30 or more GPIO and basic functionally, but more importantly have the IO on headers that are easy to connect to a PCB of your own design that performs a specific function. In this case the FPGA development board is more of a component and might be dedicated to one prototype. There are a number of inexpensive modules from Digilent, Terasic and other vendors that might be ideal. You can make some pretty useful things with one of these modules and PCB vendors offering free layout and design tools like ExpressPCB. Here are some specific considerations in making a choice:
What kind of documentation is provided?
What kind of customer support is available?
What kinds of demo projects are available and can I actually build them with my tool version
Now of course merely understanding the manuals for clocking, IO, and other resources of a particular device isn't sufficient. You need to be able to make use of the device datasheet, especially the AC specifications. To give you an idea here is a table of useful switching specifications for a number of Digilent boards that I own ( the CMOD-A7 is an Artix-1 device ).
For Spartan6-3 (Network)
SDR LVDS transmitter or receiver (using IOB SDR register) 400 Mb/s
DDR LVDS transmitter or receiver (using IOB ODDR2/IDDR2 register) 800 Mb/s
SDR LVDS transmitter (using OSERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
DDR LVDS transmitter (using OSERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
SDR LVDS receiver (using ISERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
DDR LVDS receiver (using ISERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
You also need to understand thermal management. Some of these boards don't have much copper mass and do have a lot of heat dissipating
components in a very small area. It is likely that you will have issues trying to push these modules to the extreme limits for an application
even with their limited power supply resources.
If what you need is for some custom logic and <100 MHz switching and a few are output pins then you aren't likely to have problems, assuming that
you properly terminate your IO signals. Since you are competent doing digital and analog design you know the differences between a .1" header
and and HSMC or FMC connector as far as signal integrity characteristics are concerned. You also understand from the FPGA vendor's literature the
termination requirements for all supported logic standards and clocking limitations.
Case 5:
1) "Less than $2000" AND
2) "I want to experiment with using advanced IO resources" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably
competent designing with digital, analog or mixed-signal devices."
In order to get experience using the advanced IO features or transceivers available in current generation FPGA devices you need a board that is designed to allow
you to use these features. I bought a Genesys2 primarily because the way that they implemented mDP allowed me to experiment with multi-lane transceiver designs. The
HPC FMC connector was a bonus but you have to do your homework if you plan on using a mezzanine board and the FMC connector. In particular, there are a lot of "FMC" mezzanine cards that aren't necessarily suitable for the Genesys2 FMC implementation or are even particularly VITA-57 compliant. Usually, this has to do with clocking and IO bank pin assignments. If you want to use a particular FPGA carrier board with a particular FMC type mezzanine card you have to trace through all of the pin assignments to make sure of compatibility. This is particularly true for differential LVDS IOSERDIES2 applications. In general it's easier to find an HSMC mezzanine card FPGA carrier board combination but you still have to do your homework as there are differences between differential signal pairs routed as differential pairs and differential signal pairs simply having matched trace lengths. If you have a bus of differential signals trace length matching across pairs is important. I've used the Nexys Video and Genesys2 boards for a number of projects using the FMC mezzanine cards with complete success. I've not been able to use either of those boards to connect every FMC card that I wanted to use. It is unlikely that you will find an FMC mezzanine card designed to work with an Intel based FPGA board that can be used on a Xilinx based FPGA board. It all has to do with pin assignments. This isn't a deficiency of the FMC implementation of the Digilent boards are even of the mezzanine boards, just an incompatibility for particular FPGA device pin locations and signal assignments.
If you only get one takeaway from this thread this is it... just because it's on an FMC or HSMC connector doesn't mean you can use it with your FMC or HSMC equipped FPGA board.
Digilent's current crop of FPGA boards provides either low speed PMOD connectors (<10 MHz) which are ease to connect to a custom PCB or high density FMC connectors which are expensive and difficult to connect to a custom PCB. No one knows what the so called high-speed PMODs were designed to do, but they aren't suitable for advanced IO experimentation.
If you want to experiment with transceivers you need to read the Xilinx transceiver user manual and know the difference between GTP, GTH and GTY transceiver implementations and maybe those from other vendors.
Before choosing a general purpose board to explore advances IO I suggest:
Have a thorough understanding of advanced constraints beyond location and IOSTANDARD. There are user manuals for this.
Have competence in timing closure methodologies. Read the manuals.
Thoroughly understand the Series7 IO, clocking, and transceiver users' manuals
Pore over the board documentation, especially the schematics, for boards on your short list.
A lot of FPGA board vendors will make you do the work to figure out which banks specific IO pins are assigned to.
Make sure that the support includes applicable demo projects that you can build them targettin that particular board with your version of Vivado easily.
Figure out what IP if any you need to do something useful with your advanced IO plans.
Case 6:
1) "The minimal to accomplish the project" AND
2) "I have a very specific project to complete using specific advanced IO resources" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably
competent designing with digital, analog or mixed-signal devices."
For this case the analysis gets complicated. If you want need to do video or Ethernet based communication there might be a board that fits your specific
needs for a particular project. The general rule is that buying hardware that isn't designed to accomplish a particular purpose is rarely a good investment. 10G
Ethernet is a different animal than Gigabit Ethernet. 12G SDI video is a different animal than HDMI video. You need to verify that either the board can do what you want
to do or provides the IO in a form that let's you add a mezzanine card to it to do the job. Neither of these investigations is necessarily straightforward or easy.
So by now you probably realize that each of the cases that I posit involve building an ever increasing level of competence and body of expertise. So everything that applies to the previous cases applies here except that you now have to select all of the boards that will allow you to complete your project. If you need to have a temporoary or time-restricted license to complete your project then what good will that be next year?
Clearly I haven't addressed all of the possible scenarios for the three questions put forth in the beginning but hopefully I've presented the basic ideas for a wide range of people willing to take the time to read it. One case that I didn't address is where you want to do something using one of the many PMODs available for purchase and want to create an HDL solution to accomplish something. Again, the cheapest board available with the most standard PMODs will likely be what you
want. Make sure that you understand what will be provided for you and what you needs to do for yourself. This is a small universe but one in which a lot of people will happily spend there lives.
A lot of what's been presented is 'common sense', whatever that is. If you've never ridden a bike but saw the Tour de France and want to dip your toe into competitive racing the first thing to do is not spend 100's of dollars on shoes, helmets, clothes and $10K on a road bike that's just over your wildest budget ( you know because you're going to grow into it...). If, once you know what you're doing, you decide that you want to do mountain trail racing none of that gear will be useful. Also learning
how to ride in the company of a local bike club will be much more productive and fun than spending weeks on the couch reading books on technical riding concepts.
I hope that this provides some things to consider for the many of you not having the experience with a lot of FPGA development boards and projects. I apologize for the rough formatting....
Question
zygot
I really don't know where to put this so I decided to ask myself a question and then propose an answer. Perhaps there needs to be a new home for basic assistance for users.
A frequent question for beginners and even experienced people resolves around how to select an FPGA development board. The answer depends on what you want to do with it. The analysis can be anywhere from simple to complex. But there are three issues to resolve that will simplify the process of making a selection.
Three questions that only you can answer are:
For our context I'll be ignoring a 4th question, which might be the real driver for your interest. That question is: "What are your goals?". If you are just curious then that's different than if you want to add marketable skills to your resume. Also, you might perceive knowing how to develop with a particular device, such as Zynq, as an over-arching motivation. My view is that the Zynq is a great solution for a number of problems for a competent FPGA developer but except for running Ubuntu almost anything
that I can do in software can be done with logic resources in an FPGA. On the theory that goals tend to change with experience and knowledge I'm going to proceed without answering that question.
So let's group some possible answers to the responses to the previously listed questions and provide a bit of guidance.
Case 1:
1) $0 OR
2) either "I don't know" or "I just want to learn how to use an FPGA". OR
3) None
If you don't have a specific hardware project requiring an FPGA you don't need to spend anything to learn or develop FPGA applications and I suggest that you don't. Just get the latest version of Vivado or ISE. You can do everything except spend time debugging hardware with nothing more than Vivado or ISE. If you have no experience with VHDL or Verilog then I strongly suggest buying a used textbook but this is not a requirement. Xilinx provides information about how to use its devices and tools but assumes that you know enough about an HDL to accomplish synthesis or simulation for a project. Learning an HDL in the context of a directed or group setting is easier than teaching yourself, but not necessary. FPGA devices are complex and the tools are complex and no one is going to spend a Saturday afternoon reading the Xilinx literature and being a competent FPGA developer by Sunday. Understand that FPGA development is really just digital logic development. So if you come from a software background you might have to re-wire your brain a bit to grasp the basic concepts. Learn the basic concepts, how to be fluent in an HDL for both synthesis and simulation and how to know how to simulate effectively. You simply can't do competent FPGA development unless you know how to write a testbench in your HDL and perform effective simulation.
You don't need to read the vendor manuals for the resources in any particular FPGA device but having an understanding of what and FPGA is certainly can't hurt.
Case 2:
1) "not much" AND
2) "Nothing in particular but simple logic designs" AND
3) I'm competent using an HDL, simulator tools, and Vivado or ISE
If these are your answers then the advice for case 1 might still be valid. It's true that most of us need some form of positive feedback to motivate us to do hard work. An FPGA development board might just do the trick. So my advice is simple. Spend the least amount possible. There are decent boards with a JTAG programming and minimal interface resources available such as the CMOD or DE0-NANO for < $100. Aside from the motivation factor you still don't need hardware to accomplish even complicated designs so why spend money until you know what to spend you money on? If you are determined to spend your allowance then start off with the least expensive and least expensive to replace board. The buttons, LEDs and switches can all be simulated. For basic HDL designs you can use global clock buffers and not worry about anything except pin location constraints.
Case 3:
1) "not much" AND
2) "I want to use and FPGA to build a variety of hardware prototypes that don't require using advanced FPGA IO features" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably competent designing with digital, analog or mixed-signal devices."
For this case there are a number of inexpensive modules that offer 30 or more GPIO and basic functionally, but more importantly have the IO on headers that are easy to connect to a PCB of your own design that performs a specific function. In this case the FPGA development board is more of a component and might be dedicated to one prototype. There are a number of inexpensive modules from Digilent, Terasic and other vendors that might be ideal. You can make some pretty useful things with one of these modules and PCB vendors offering free layout and design tools like ExpressPCB. Here are some specific considerations in making a choice:
Now of course merely understanding the manuals for clocking, IO, and other resources of a particular device isn't sufficient. You need to be able to make use of the device datasheet, especially the AC specifications. To give you an idea here is a table of useful switching specifications for a number of Digilent boards that I own ( the CMOD-A7 is an Artix-1 device ).
Nexys Video Genesys2 ATLAS
Artix(-1) Kintex(-2) Spartan6(LX-3)
DS181 DS182 DS162
----------- ----------- --------------
Fmax_bufg 464 710 400
Fmax_bufh 464 710 -
Fmax_bufr 315 540 -
Fmax_bufio 600 800 -
Fmax_bufio2 - - 525
Fmax_buffpll - - 1050
Fmax_buffgmux - - 400
PLL_Finmax 800 933 525
PLL_Finmin 19 19 19
PLL_Foutmax 800 933 1050
PLL_Finmain 6.25 6.25 3.125
PLL_vcomax 1600 1866 1050
MMCM_Finmax 800 933 -
MMCM_Finmin 10 10 -
MMCM_Foutmax 800 933 -
MMCM_Finmain 4.69 4.69 -
Fmax_bram_xxx 297-388** 427-544** 280
Fmax_fifo 388* 544* -
Fmax_dsp48e 177-464** 249-650** -
Fmax_dsp48a - - 333**
All values in MHz
- not applicable
* non-ECC mode
** depends on modes used
[Update] Interesting SERDES performance specifications:
Kintex-2 Artix-1
SDR LVDS transmitter (using OSERDES; DATA_WIDTH = 4 - 8 HR 710 600 Mb/s
HP 710 - Mb/s
DDR LVDS transmitter (using OSERDES; DATA_WIDTH = 4 to 14) HR 1250 950 Mb/s
HP 1400 - Mb/s
SDR LVDS receiver (SFI-4.1)(1) HR 710 600 Mb/s
HP 710 - Mb/s
DDR LVDS receiver (SPI-4.2)(1) HR 1250 950 Mb/s
For Spartan6-3 (Network)
SDR LVDS transmitter or receiver (using IOB SDR register) 400 Mb/s
DDR LVDS transmitter or receiver (using IOB ODDR2/IDDR2 register) 800 Mb/s
SDR LVDS transmitter (using OSERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
DDR LVDS transmitter (using OSERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
SDR LVDS receiver (using ISERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
DDR LVDS receiver (using ISERDES2; DATA WIDTH = 2 to 8 1050 Mb/s
You also need to understand thermal management. Some of these boards don't have much copper mass and do have a lot of heat dissipating
components in a very small area. It is likely that you will have issues trying to push these modules to the extreme limits for an application
even with their limited power supply resources.
If what you need is for some custom logic and <100 MHz switching and a few are output pins then you aren't likely to have problems, assuming that
you properly terminate your IO signals. Since you are competent doing digital and analog design you know the differences between a .1" header
and and HSMC or FMC connector as far as signal integrity characteristics are concerned. You also understand from the FPGA vendor's literature the
termination requirements for all supported logic standards and clocking limitations.
Case 5:
1) "Less than $2000" AND
2) "I want to experiment with using advanced IO resources" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably
competent designing with digital, analog or mixed-signal devices."
In order to get experience using the advanced IO features or transceivers available in current generation FPGA devices you need a board that is designed to allow
you to use these features. I bought a Genesys2 primarily because the way that they implemented mDP allowed me to experiment with multi-lane transceiver designs. The
HPC FMC connector was a bonus but you have to do your homework if you plan on using a mezzanine board and the FMC connector. In particular, there are a lot of "FMC" mezzanine cards that aren't necessarily suitable for the Genesys2 FMC implementation or are even particularly VITA-57 compliant. Usually, this has to do with clocking and IO bank pin assignments. If you want to use a particular FPGA carrier board with a particular FMC type mezzanine card you have to trace through all of the pin assignments to make sure of compatibility. This is particularly true for differential LVDS IOSERDIES2 applications. In general it's easier to find an HSMC mezzanine card FPGA carrier board combination but you still have to do your homework as there are differences between differential signal pairs routed as differential pairs and differential signal pairs simply having matched trace lengths. If you have a bus of differential signals trace length matching across pairs is important. I've used the Nexys Video and Genesys2 boards for a number of projects using the FMC mezzanine cards with complete success. I've not been able to use either of those boards to connect every FMC card that I wanted to use. It is unlikely that you will find an FMC mezzanine card designed to work with an Intel based FPGA board that can be used on a Xilinx based FPGA board. It all has to do with pin assignments. This isn't a deficiency of the FMC implementation of the Digilent boards are even of the mezzanine boards, just an incompatibility for particular FPGA device pin locations and signal assignments.
If you only get one takeaway from this thread this is it... just because it's on an FMC or HSMC connector doesn't mean you can use it with your FMC or HSMC equipped FPGA board.
Digilent's current crop of FPGA boards provides either low speed PMOD connectors (<10 MHz) which are ease to connect to a custom PCB or high density FMC connectors which are expensive and difficult to connect to a custom PCB. No one knows what the so called high-speed PMODs were designed to do, but they aren't suitable for advanced IO experimentation.
If you want to experiment with transceivers you need to read the Xilinx transceiver user manual and know the difference between GTP, GTH and GTY transceiver implementations and maybe those from other vendors.
Before choosing a general purpose board to explore advances IO I suggest:
Case 6:
1) "The minimal to accomplish the project" AND
2) "I have a very specific project to complete using specific advanced IO resources" AND
3) "I'm competent using an HDL, simulator tools, and Vivado or ISE plus I'm reasonably
competent designing with digital, analog or mixed-signal devices."
For this case the analysis gets complicated. If you want need to do video or Ethernet based communication there might be a board that fits your specific
needs for a particular project. The general rule is that buying hardware that isn't designed to accomplish a particular purpose is rarely a good investment. 10G
Ethernet is a different animal than Gigabit Ethernet. 12G SDI video is a different animal than HDMI video. You need to verify that either the board can do what you want
to do or provides the IO in a form that let's you add a mezzanine card to it to do the job. Neither of these investigations is necessarily straightforward or easy.
So by now you probably realize that each of the cases that I posit involve building an ever increasing level of competence and body of expertise. So everything that applies to the previous cases applies here except that you now have to select all of the boards that will allow you to complete your project. If you need to have a temporoary or time-restricted license to complete your project then what good will that be next year?
Clearly I haven't addressed all of the possible scenarios for the three questions put forth in the beginning but hopefully I've presented the basic ideas for a wide range of people willing to take the time to read it. One case that I didn't address is where you want to do something using one of the many PMODs available for purchase and want to create an HDL solution to accomplish something. Again, the cheapest board available with the most standard PMODs will likely be what you
want. Make sure that you understand what will be provided for you and what you needs to do for yourself. This is a small universe but one in which a lot of people will happily spend there lives.
A lot of what's been presented is 'common sense', whatever that is. If you've never ridden a bike but saw the Tour de France and want to dip your toe into competitive racing the first thing to do is not spend 100's of dollars on shoes, helmets, clothes and $10K on a road bike that's just over your wildest budget ( you know because you're going to grow into it...). If, once you know what you're doing, you decide that you want to do mountain trail racing none of that gear will be useful. Also learning
how to ride in the company of a local bike club will be much more productive and fun than spending weeks on the couch reading books on technical riding concepts.
I hope that this provides some things to consider for the many of you not having the experience with a lot of FPGA development boards and projects. I apologize for the rough formatting....
Link to comment
Share on other sites
3 answers to this question
Recommended Posts
Archived
This topic is now archived and is closed to further replies.