Author Topic: FPGA beginner  (Read 8439 times)

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Offline gonnafail

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FPGA beginner
« on: November 25, 2010, 04:40:12 PM »
I have an upcoming project where I will need to receive, decode, then retransmit HDMI video signals. I plan on using the Texas Instruments HDMI transmitter receivers and have come to the decision that this will need to be done with an FPGA. The problem is I have very little experience with FPGAs. I have done some code modifications on boards at work and I took a couple of courses at school on VHDL. I was wondering if anyone had any good resources for learning FPGA development. Either Alterra or Xilinx is fine. Ideally I would like a reasonably priced Development board with a series of lessons meant to be used with it to get me started. The main requirement being that the FPGA on the dev board be capable of HDMI input/output.

I have found a lot of various development boards out there but most seem to be quite expensive with very little resources for a beginner. I am hoping to find something less than $800 CDN with a decent level of support behind it.



Offline allanw

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Re: FPGA beginner
« Reply #1 on: November 25, 2010, 07:10:38 PM »
I started an FPGA project recently and found this board to be very cheap, at least at academic pricing.

http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,836&Prod=ATLYS

It has HDMI.

Offline joelby

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Re: FPGA beginner
« Reply #2 on: November 25, 2010, 11:11:15 PM »
There's a nice book called FPGA Prototyping Using Verilog Examples (also available in VHDL), which was written for Digilent's Nexys2 board, but some of the examples might apply. The ATLYS looks great for your application, gonnafail, and also mine - thanks allanw, I might actually redesign the thing I'm in the midst of making for the Nexys2 to use it, because it has a nice impedance controlled, matched differential pair connector. The Nexys2's expansion port has arbitrary length traces and differential pairs are scattered every which way!

Offline joelby

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Re: FPGA beginner
« Reply #3 on: November 26, 2010, 01:07:50 AM »
Just thought I'd mention (because I just discovered it myself) that Xilinx has some interesting free resources online:

http://www.xilinx.com/training/free-video-courses.htm
http://www.xilinx.com/university/students/index.htm (click Resources)

Offline gonnafail

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Re: FPGA beginner
« Reply #4 on: November 26, 2010, 02:48:48 AM »
I am going to have to take a closer look at that Atlys development board but that looks to be perfect for my needs. Quite reasonably priced too. I looked at a lot of development boards and was having a hard time finding one with two HDMI ports, this one has four! I had also stumbled across the Xilinx training, Altera has similar here: http://www.altera.com/education/training/curriculum/fpga/trn-fpga.html Does anyone know of a good support forum? Book recommendations? any other information on FPGA design? Advice for beginner?

Thanks for the information already given, that has been very helpful already.

Offline joelby

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Re: FPGA beginner
« Reply #5 on: November 26, 2010, 03:19:35 AM »
Xilinx hosts its own forum, which seems to be heavily used and has some very helpful contributors.

fpga4fun.com has some interesting projects for getting started with, though I found that reasons for using particular coding styles weren't always explained in enough detail (but other resources filled in the gaps).

The comp.arch.FPGA news group is also surprisingly busy: http://groups.google.com/group/comp.arch.fpga/topics


Offline allanw

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Re: FPGA beginner
« Reply #6 on: November 26, 2010, 04:00:22 AM »
There's a nice book called FPGA Prototyping Using Verilog Examples (also available in VHDL), which was written for Digilent's Nexys2 board, but some of the examples might apply. The ATLYS looks great for your application, gonnafail, and also mine - thanks allanw, I might actually redesign the thing I'm in the midst of making for the Nexys2 to use it, because it has a nice impedance controlled, matched differential pair connector. The Nexys2's expansion port has arbitrary length traces and differential pairs are scattered every which way!



This will be long but I spent a while researching connectors...

Unfortunately, to buy the VHDCI mating plug they used on the Atlys board, you have to get it shipped from Taiwan with a $100 shipping charge...

There are alternatives, but they are a bit strange:


Samtec sells an edge-mount plug: http://samtec.com/ProductInformation/TechnicalSpecifications/Overview.aspx?series=VHDCP

For this plug, I believe the differential pairs are set up so that one signal of the pair is on the bottom layer and the other is on the top layer. So this means you'll have one via change imbalance. The connector is about $10, but you can get a few free samples which is nice.


Molex also has one: http://www.molex.com/molex/products/datasheet.jsp?part=active/0714253001_IO_CONNECTORS.xml&channel=Products&Lang=en-US

But the mounting method is a bit weird. I think it's through-hole but you need to get rectangular slots cut into your PCB.


I just found out about this board: http://www.xilinx.com/products/devkits/EK-S6-SP601-G.htm

It has the industry standard FMC connector on it, but you have to pay $100 to buy the specification just to see the pinout. Shoot, if I'd known this board existed I would have bought it instead of the Atlys.

Offline joelby

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Re: FPGA beginner
« Reply #7 on: November 26, 2010, 12:30:30 PM »
Unfortunately, to buy the VHDCI mating plug they used on the Atlys board, you have to get it shipped from Taiwan with a $100 shipping charge...


It's odd that Digilent don't stock this connector - they sell the Nexys2's Hirose FX2 connector. I recommend buying the VHDCI expansion boards and unsoldering the connectors! If you get the breadboard one, you end up with a nice big breadboard for only a few dollars more than the connector would have cost anyway.

Quote
Molex also has one:
But the mounting method is a bit weird. I think it's through-hole but you need to get rectangular slots cut into your PCB.


Hmm, that looks like an IDC connector to me. How about this Molex part? Unfortunately it looks like element14 only sell the receptacle connector - I assume that the expansion board uses the plug. Would you mind confirming this by looking at the edge of your board, before I buy something I don't need?

Samtec also do a through-hole version, but it's more expensive and less in-stock than the Molex one, and also a receptacle.

Offline gonnafail

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Re: FPGA beginner
« Reply #8 on: November 26, 2010, 12:46:26 PM »
Quote
Unfortunately, to buy the VHDCI mating plug they used on the Atlys board, you have to get it shipped from Taiwan with a $100 shipping charge...


Correct me if I am wrong but isn't this the connector available at digikey for about $15?
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=WM7320-ND

Worst case you could always buy one of their expansion boards for $30-$40 and steal the connector off of that. I would hate to be the one doing all the desoldering on that but I would if it saved me spending more than $100 on a connector.

Offline joelby

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Re: FPGA beginner
« Reply #9 on: November 26, 2010, 12:54:21 PM »
That looks like the receptacle rather than the plug. It doesn't look like anyone makes a board-mounted plug, other than Digilent's not-stocked-by-anyone supplier, so it might be necessary to just use two receptacles and a VHDCI cable assembly.

Offline allanw

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Re: FPGA beginner
« Reply #10 on: November 26, 2010, 01:24:39 PM »
VHDCI male-male cables are insanely expensive since they're intended for the enterprise-y SCSI market. The cheapest ones you can buy from regular stores are like $80+.

I sure as hell am not going to pay $30 for their prototype boards just to desolder the connector.

I've decided to just design for the Samtec edge-mount connector since they're only $10 and live with the extra via change. It shouldn't make a huge difference. One extra disadvantage is that the product datasheet recommends using a thickness of 0.039" instead of the regular 0.063". But I'm sure a little bending of the pins will make it work OK...

edit: Emailed Digilent with:

"It's rather unfortunate that you do not sell these connectors. How can you expect people to develop their own boards for the Atlys for prototyping use if the only option is to get the VHDCI plugs direct from Taiwan? I was quoted a shipping charge of $100."
« Last Edit: November 26, 2010, 01:32:38 PM by allanw »

Offline joelby

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Re: FPGA beginner
« Reply #11 on: November 26, 2010, 01:31:21 PM »
VHDC cables are insanely expensive since they're for SCSI. The cheapest ones you can buy from regular stores are like $80+.

I sure as hell am I not going to pay $30 for their prototype boards just to desolder the connector.

I've decided to just design for the Samtec edge-mount connector since they're only $10 and live with the extra via change. It shouldn't make a huge difference.


I just had a quick look on eBay and inexpensive (well, <$50) VHDCI connectors abound. There are even some that come in ridiculous lengths.

Making up a short cable with two IDC connectors should be straightforward if you have a vice, and only cost you a bit more than 2 * $10, plus a $10 receptacle, but unless Digilent start stocking the connector I think I'll have to use the Samtec part too :(

gonnafail, sorry to get off topic here - hopefully with all the HDMI ports on board you won't need to worry external expansion!

Offline gonnafail

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Re: FPGA beginner
« Reply #12 on: November 26, 2010, 02:23:36 PM »
gonnafail, sorry to get off topic here - hopefully with all the HDMI ports on board you won't need to worry external expansion!

No problem, I always welcome a healthy discussion. While heading off topic at least this thread has remained "troll free". In adding to the connector issue from the Atlys reference manual which you can download from the previously linked site at the top of the tread. It shows the board as having the "male" type plug in which case the $15 receptacles are what you need. If anyone has this board it would be great to hear confirmation from them on this though.

It is true that with all the HDMI ports I myself will not need the expansion, at least not for this project but it is something worth noting before purchasing as who knows what you will be doing in the future. The way I look at it if they are able to sell expansion boards for $30 with the header then there must be a reasonably priced source out there somewhere. It would be much more convenient and make sense if you could buy these connectors from digilent seeing as they are supplying the connectors to other boards. That being said if I were designing an expansion board and the connector is one that I could get from digikey, I would order it from them with all the rest of my parts and not bother with a second supplier. This could be why they have decided not to carry this specific connector if it is easily available from other distributers.

Offline allanw

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Re: FPGA beginner
« Reply #13 on: November 26, 2010, 02:27:26 PM »
Perhaps they get the boards manufactured and assembled directly in Asia without having to stock all the parts themselves. That would explain why they do not sell the connectors. Hopefully if they get some customer demand for them then they'd at least consider it.

I will be receiving the board on Monday and I will confirm. However, from the small pictures on their site, it appears like it is indeed the receptacle on the main board and plugs on the prototyping boards.

Offline joelby

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Re: FPGA beginner
« Reply #14 on: November 26, 2010, 02:33:07 PM »
In adding to the connector issue from the Atlys reference manual which you can download from the previously linked site at the top of the tread. It shows the board as having the "male" type plug in which case the $15 receptacles are what you need. If anyone has this board it would be great to hear confirmation from them on this though.

Do you mean the diagram on page 17? You're right, and it would make sense for them to do it this way. Hopefully I'll have mine on Monday or Tuesday and will report back if allanw hasn't already.

Quote
That being said if I were designing an expansion board and the connector is one that I could get from digikey, I would order it from them with all the rest of my parts and not bother with a second supplier. This could be why they have decided not to carry this specific connector if it is easily available from other distributers.

True. While the Hirose FX2 connector is available from element14, there are a bunch of different companies making VHDCI connectors. I don't see why Digilent wouldn't just sell one with their own mark-up, though. Chances are they just haven't got around to it yet, because it's such a new product.


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