Poll

Which form factor do you want to see

Gum stick with dual USB-C ports
11 (47.8%)
Module with LGA land patterns
2 (8.7%)
Module with micro mezzanine connectors
10 (43.5%)

Total Members Voted: 23

Author Topic: [Poll] FPGA board form factor  (Read 5937 times)

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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #25 on: September 13, 2019, 06:34:52 pm »
1. Really seriously consider alternatives to the FT2232. It's a big cost adder and even if you need true usb-fifo-gpio functionality a cheaper micro can usually do the job for under $1.
2. Please avoid SiTime MEMS oscillators. They cost more than surface mount TCXOs and the performance is way inferior to cheap smd powered crystal oscillators, which are easy to find on LCSC.
3. The choice of connectors seem on the expensive side; I would suggest starting your search on LCSC rather than digikey/mouser because you will often find low cost good quality connectors from Japanese or Taiwanese manufacturers that you won't find on digikey.
4. Also maybe add a pdf schematic because I can't open those files. Better idea, switch to kicad/geda or at least easyeda  ;)
5. 47uF isn't a very large capacitance for standard MLCC at 1.0V. That tantalum has an ESR of 300mOhm which is kind of shitty (a 22uF MLCC will have < 100mOhm). I would recommend 2 x 22uF 0603 MLCC caps instead; you probably don't want to use just a single cap for the entire 1.0V rail (I would go for 4 caps, one for each "side" of the FPGA, but 2 most likely will work).

1. FT2232H is a must. Gowin's official programmer software uses FT2232H's MPSSE mode to implement JTAG. I can dumb it down to FT232H, but for $0.8 saving, neutering a second channel which can be used for UART, is not the best option.

2. FT2232H is stupid. Its PLL doesn't take in the standard 24MHz, but 12MHz. The lower the frequency, the larger the physical size the resonator has to be. For 12MHz, there's no resonators or oscillators available in the size I'm looking for (2016/1612).

3. Size. Molex 503480 is the only part I can find that can pack 32 pins at 0.5mm pitch into an 18mm overall width (0.4mm is too hard on customer's board, if someone can easily deal with 0.4mm FPC, they won't need a breakout for 0.4mm QFN88). I can only fit a 26 pin FPC than the current 32 pin one if I use Omron XF2/3, so I have to nerf the system 5V, IO 3.3V, I2C and push button pins. The Molex USB connector can be replaced with exact Chinese copy, but the shipping is not worth it (unless JLCPCB can ship parts with PCB without stuffing them).

I'm not stuffing the boards by JLC. Trump tax is too much for anything more than $400 (personal tax exemption limit), so is Xi tax for US parts without an import/export tax exemption license. The cheapest way for me would be PCB by JLC or JDB, and all active parts from Mouser/DK, then stuff the parts in the US.

4. In the next release (hopefully today) I will include a PDF schematic plot and in future, PCB plot. I'm just too used to Altium, though I'm learning KiCAD. Maybe I will eventually release it in KiCAD format if I plan to hit HaD.

5. Good idea. I changed it to 4*10uF 0402 6.3V X5R from Murata (8uF at 1V bias). Overall cost is around halved, and I have much better routing flexibility, while I no longer have to deal with the nasty moisture absorption issue with tantalum caps.
 

Offline SiliconWizard

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Re: [Poll] FPGA board form factor
« Reply #26 on: September 13, 2019, 08:02:55 pm »
1. FT2232H is a must. Gowin's official programmer software uses FT2232H's MPSSE mode to implement JTAG. I can dumb it down to FT232H, but for $0.8 saving, neutering a second channel which can be used for UART, is not the best option.

Yep. Funny how many people go bonkers as soon as they see the word "FTDI" somewhere. Yet FTDI parts are everywhere. And they just work.
And yes, for JTAG access, they are great. Many vendors' programmers use them, because their MPSSE engine works great for JTAG/SWD, and is trouble-free.

Just one suggestion. If it's "routable"... because your board's going to be pretty dense already.
It would be nice if you routed all required signals from the second channel of the FT2232H to access it as synchronous FIFO (I don't remember if you can use the second channel in synchronous mode, something to check). That's basically an 8-bit data bus, a clock out signal and a few control pins. The synchronous FIFO mode is the only one with which you can get the max data throughput (~30MBytes/s in practice).

Ignore that if 1/ channel two can't be used in this mode and 2/ you don't have enough room to route that, or enough spare IOs...
But just saying, I find it a shame that many dev boards using a FT2232H or FT232H don't allow you to use synchronous FIFO mode. UART only access gets you like 300KB/s max (for the highest baud rate of 3MB/s), asynchronous FIFO mode, only like 8MBytes/s max (which is already much better), but for only 1 additional pin (the clock), you can get the full throughput...
« Last Edit: September 13, 2019, 08:07:03 pm by SiliconWizard »
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #27 on: September 13, 2019, 08:54:37 pm »
Just one suggestion. If it's "routable"... because your board's going to be pretty dense already.

It's a bit challenging considering I don't even have enough pins, let alone routing space...

« Last Edit: September 13, 2019, 09:57:24 pm by blueskull »
 

Offline SiliconWizard

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Re: [Poll] FPGA board form factor
« Reply #28 on: September 13, 2019, 08:57:52 pm »
Ok nevermind... maybe you can think about that for a bigger dev board or something.
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #29 on: September 13, 2019, 08:59:59 pm »
Ok nevermind... maybe you can think about that for a bigger dev board or something.

Maybe I'll use that as an incentive to get my bit bang USB HS PHY to work.
 

Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #30 on: September 14, 2019, 01:56:23 am »
I think you are overestimating the tariffs. The cost difference between mouser/dk and shenzhen market more than makes up for the tariffs. I think a better option is to do everything from china and ship directly to end users while underdeclaring value. Most of the parts you are using don't really need to be imported.
 
I still think more effort needs to be put in BOM cost reduction because at $20 (and that doesn't include assembly) you will probably have to sell at $50 or so, which is a bit much for a module that people are going to incorporate into projects. de0-nano has existed for years at a lower price point so why wouldn't people just buy that?

If JTAG is for programming only, look into implementing the protocol on a micro and providing your own programming software. USB FS is fast enough to transfer the bitstream in 1-2 seconds.

$1.5 for a fpc connector is BS. I would move decoupling caps to the bottom of the board and use an ordinary FPC connector. Specialized parts should be avoided whenever possible.

With a bit of effort I think the BOM cost can be reduced to $10 or so, which means a sell price of $25 which is far more competitive.
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Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #31 on: September 14, 2019, 03:16:26 am »
A 1 minute search found this: https://item.szlcsc.com/305537.html which fits 30 pins into 17mm. Really look harder and look beyond the western brands next time ;) not to mention Molex is known for subpar quality given the price.
« Last Edit: September 14, 2019, 03:18:02 am by OwO »
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #32 on: September 14, 2019, 03:35:29 am »
1. I think you are overestimating the tariffs. The cost difference between mouser/dk and shenzhen market more than makes up for the tariffs. I think a better option is to do everything from china and ship directly to end users while underdeclaring value. Most of the parts you are using don't really need to be imported.
 
2. I still think more effort needs to be put in BOM cost reduction because at $20 (and that doesn't include assembly) you will probably have to sell at $50 or so, which is a bit much for a module that people are going to incorporate into projects. de0-nano has existed for years at a lower price point so why wouldn't people just buy that?

3. If JTAG is for programming only, look into implementing the protocol on a micro and providing your own programming software. USB FS is fast enough to transfer the bitstream in 1-2 seconds.

4. $1.5 for a fpc connector is BS. I would move decoupling caps to the bottom of the board and use an ordinary FPC connector. Specialized parts should be avoided whenever possible.

5. With a bit of effort I think the BOM cost can be reduced to $10 or so, which means a sell price of $25 which is far more competitive.

6. A 1 minute search found this: https://item.szlcsc.com/305537.html which fits 30 pins into 17mm. Really look harder and look beyond the western brands next time ;) not to mention Molex is known for subpar quality given the price.

1. Most of my parts are cheaper in Mouser than LCSC, rest of some connectors and RLCs. Since you later mentioned that HRS connector, I think that should justify the shipping, and I will move some RLCs and other possible parts to LCSC.

I don't have to under declare. If FOB price is below a certain value (~$100), personal import tax is exempted in most countries.

But since I'm in USA, if I stuff all boards in China, the large batch of 100 will certainly exceed the exemption and I don't want to mess with US customs.

As for distribution, I don't want to use ePacket as it's not available to common people, and China Post EMS is actually more expensive than USPS, so shipping from US at low quantity is actually cheaper.

2. Try to plug DE10-N into a DIP socket. Yes, I have that board, and I have even made an official tutorial series for TerASIC on DE10-STD based on Cyclone V SX.

3. JTAG can be used for logic analyzing, which is supported by Gowin chips. If downloading is all what I need, yes, I can use nothing but an USB MCU or even USB SPI bridge to talk to the GD25 while keeping FPGA in reset (high-Z).

4. I took your advice and replaced with that HRS part.

5. Without FTDI, $12 should be possible.

6. That's wonderful.
 

Online BravoV

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Re: [Poll] FPGA board form factor
« Reply #33 on: September 14, 2019, 03:45:04 am »
As enthusiast, just want to say I am grateful and conveying my appreciations reading the intense technical discussions of you two.  :-+

Back into observing, learning and lurking mode.

Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #34 on: September 14, 2019, 04:15:03 am »
1. ePacket is actually available to individuals; I ship like 5 packages a month and they still keep my account open. You have to first register on shipping.ems.com.cn (I just filled in "N/A" for 公司名称 and they didn't say anything about it), then contact EMS customer service to ask them to activate your account. (You need someone who can speak chinese for this part). The prices are posted here: http://shipping.ems.com.cn/product/findDetail?sid=400032

One thing to be careful about is China Post and EMS are separate divisions, and if you walk into a random China Post office they will know absolutely NOTHING about ePacket and quote you outrageous prices. You must go to a EMS logistics office which are more rare; one way to tell is that these look far more messy (big room, packages on the floor everywhere).

In shenzhen there are also proxy shipping services that will let you access far more shipping methods (e.g. postNL which is cheaper for EU destinations, and other methods that allow shipping lithium batteries). The prices are comparable to ePacket. You only need to take a short walk around HQB to find these. There are so many misconceptions about shipping from china on the internet that I don't know where to begin.

2. https://shop.trenz-electronic.de/en/TEI0003-02-CYC1000-with-Cyclone-10-FPGA-8-MByte-SDRAM?c=480
For a rough overview of market position:
$18 - Anlogic EG4, 20000 LE - https://www.seeedstudio.com/Sipeed-TANG-PriMER-FPGA-Development-Board-p-2881.html
$35 - Cyclone 10, 25000 LE, small form factor - CYC1000
$60 - Artix 7, 100k LE - "QMTECH core board"

3. OK that makes sense. In that case I would put the effort into looking for a clone or make a clone  ;)
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #35 on: September 14, 2019, 04:49:15 am »
1. ePacket is actually available to individuals; I ship like 5 packages a month and they still keep my account open.

3. OK that makes sense. In that case I would put the effort into looking for a clone or make a clone  ;)

1. Only if I have a manufacturing/shipping agent in China.

3. Do you want a few IOs reserved and connected to FPGA JTAG in case you want to have fun? Tentatively I'm choosing GD32F150 in QFN2832 package with external 24MHz crystal (also allows small size, low cost and clock sharing with FPGA, 3 birds one stone).

//Edit: I was going for CH549F, but considering the lack of English documentations, I think I'll settle on GD32 for now. Cypress PSoC4 is also an option for UDB-based JTAG, but the packaging size is less than favorable. The last thing I want is another 0.4mm pitch large QFN.

//Edit 2: QFN28 package can't be used. It doesn't have low jitter clock output pin (PA8), so it can't supply clock to FPGA without excessively loading the XTAL.
« Last Edit: September 14, 2019, 07:03:49 am by blueskull »
 

Offline ali_asadzadeh

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Re: [Poll] FPGA board form factor
« Reply #36 on: September 14, 2019, 05:26:19 am »
Please Stick to Alitum ^-^
I'm a Digital Expert from 8-bits to 64-bits
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #37 on: September 14, 2019, 07:39:57 am »
@OwO: if you have a time, can you check my BOM to see if anything needs to be further optimized? It's now 100% LCSC plus manufacturer webstore.
 

Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #38 on: September 14, 2019, 11:27:44 am »
Looks pretty good now  ^-^
Make sure to use pins from the same IO bank on the stm32 for JTAG interfacing; that way DMA can be used to transfer commands quickly.
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #39 on: September 15, 2019, 08:24:52 pm »
Many changes so far:

1. FTDI JTAG/UART bridge removed, in favor of a much cheaper GD32 MCU. The MCU can communicate with FPGA using SPI (multiplexed with FLASH) and UART (multiplexed with LS01 and LS02).

2. SiTime MEMS removed, in favor of plain crystal resonator. The MCU is capable of generating clock and output a clean clock on its own, plus the FPGA is capable of cleaning up jitter using its own PLL, thus a dedicated oscillator is no longer needed.

3. Majority of passives are replaced with 0201 for a larger layout space. Non-HDI seems to be very possible now.

4. LED quantity reduced to 5, power LED also serves as Rx/Tx LED, USB mux indicator LED and multifunction push button timer indicator LED. User LEDs remain. LEDs are moved to under USB connector to optimize routing for input ferrite beads and fuses.

5. Flash replaced with DFN 2*3 package, which opens a lot of options than the GigaDevice unicorn from nowhere other than DigiKey.

6. All parts are replaced with LCSC-obtainable parts for Chinese manufacturing (JLCPLC). I'll find a solution for global distribution. I do have a store front in HK, or maybe some forum members can help?

7. Component placement is practically frozen. Unless there is a really compelling reason to change, the Visio draft should be the final placement. It is made to scale, and closely resembles final placement.

« Last Edit: September 15, 2019, 08:26:35 pm by blueskull »
 
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Online coromonadalix

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Re: [Poll] FPGA board form factor
« Reply #40 on: September 16, 2019, 12:30:48 am »
maybe add an daughter board / breakout board project for your fpc 30 pins connector ???
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #41 on: September 18, 2019, 09:10:45 am »
Schematic posted in PDF.

maybe add an daughter board / breakout board project for your fpc 30 pins connector ???

Once the main board is done, I will make a breakout board for FPC30 in a similar DIP form factor.
 

Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #42 on: September 18, 2019, 09:58:07 am »
A suggestion, you might not want to expose your real name and details like that; I think it's a good idea to always operate under fictitious names and identities and never link them; see here: https://www.eevblog.com/forum/chat/richard-stallman-(gnu-dude)-resigned/
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #43 on: September 18, 2019, 04:22:24 pm »
A suggestion, you might not want to expose your real name and details like that; I think it's a good idea to always operate under fictitious names and identities and never link them; see here: https://www.eevblog.com/forum/chat/richard-stallman-(gnu-dude)-resigned/

I want to be known, and that includes my attitude of "no f*cks given".

It's not like you can hide -- Google always knows who you really are.

As for RMS, apparently he is going to retire regardless at his age.

If he doesn't, refer to Bob Widlar. Apparently not everyone cares about PC and the consequences.
 
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #44 on: September 19, 2019, 09:19:01 am »
Revised SCH, updated placement layout by a little bit, finished PCB library.

OneDrive link remain the same: https://1drv.ms/u/s!AkXnLOXZOgKpmCRACVRCCtURDY_A?e=dHZj0R.
 
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #45 on: September 21, 2019, 11:11:02 pm »
Update: PCB footprint and placement done, ready for layout. Actual size: 17.5mm*35.0mm.



Altium 3D doesn't work properly in Parallels VM, so I had to zoom many times and switch between 2D/3D many times to try my luck in order to get the correct 3D to show. Altium/Parallels/Apple, please fix.
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #46 on: September 23, 2019, 05:42:44 am »
Post-placement revised schematic is attached, along with draft datasheet of the product.
 

Offline OwO

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Re: [Poll] FPGA board form factor
« Reply #47 on: September 23, 2019, 06:11:28 am »
What are the board specs you used? I don't see much space for vias in that picture you posted. Is there a reason you aren't putting components on the bottom side?
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Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #48 on: September 23, 2019, 06:16:22 am »
What are the board specs you used? I don't see much space for vias in that picture you posted. Is there a reason you aren't putting components on the bottom side?

The picture is placement only, no routing or vias.

I used 0.2mm/0.45mm vias, 0.1mm traces and 0.125mm via-trace spacing. Aka, JLCPCB specs.
 

Offline blueskull

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Re: [Poll] FPGA board form factor
« Reply #49 on: September 26, 2019, 04:19:35 pm »
After almost a week of exhaustive attempts, I have to give up JLCPCB. Their 0.45mm minimum via size and 0.125mm minimum via to trace clearance makes routing very hard, impossible for me.

I have to bump up the service to WellPCB and their 0.1mm trace, 0.2mm drill, 0.1mm annular ring service. The price look the same, but that's only automatic quoting. Actual price is a YMMV thing.
 


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