The USB FPGA?

[Theo Markettos]

I've been pondering...

When it comes to attaching an FPGA to a PC, there are lots of options.
First there's JTAG, then there's RS232, then there's ethernet, and PCIe.
But there's an elephant in this room: why is USB on FPGA so hard?

Sure, every FPGA can be connected to a PC with USB, but it's usually through
a dumb bridge chip that does RS232, or maybe uses USB to bitbang JTAG. USB2
is in 'easy' territory for FPGAs at 480Mbps, while USB3 5Gbps is the same
bitrate as PCIe Gen 2. Every PC made in the last 15 years has USB.
Meanwhile, being stuck behind a bridge chip we manage single-figures Mbps.

Now there are dev boards out there with USB PHY or USB MAC chips on them,
which is all very nice, but all very painful to program. Plus they're never
there when you need them. But why should this be necessary? Any $2 junk
gadget comes with a USB2 device interface these days - I don't know what fab
process they use, but it can't be too fancy. Likewise USB microcontrollers
are a few dollars.

I realise the USB stack isn't the most friendly to implementation on FPGA -
it doesn't play nicely with FPGA SERDES for example. But if a $2 gadget can
have all the functions of a USB device on an antique process node, why don't
modern FPGAs have at least native USB2 device mode?

Theo

 

[Brane2]

Dne nedelja, 04. maj 2014 15:02:44 UTC je oseba Theo Markettos napisala:

<SNIP>

> But there's an elephant in this room: why is USB on FPGA so hard?

First, USB is crap.

Second, you need license from USB consortium in order to get you manufacturer ID code spans etc. And IIRC it was on the order of EURO 4-5K

If your inteface was a hard macro or built into a microcontroller, you might be able to get an ID or two free of charge from the producer of the chip, but without it you have to plunge the dough by yourself if you want to sell the thing as USB compatible.

Ethernet MAC span is both cheaper and less neccessary.

 

[mnentwig]

licensing, maybe?

---------------------------------------
Posted through http://www.FPGARelated.com

 

[Allan Herriman]

On Sun, 04 May 2014 12:50:28 -0700, Brane2 wrote:

Dne nedelja, 04. maj 2014 15:02:44 UTC je oseba Theo Markettos napisala:

SNIP

But there's an elephant in this room: why is USB on FPGA so hard?

First, USB is crap.

Second, you need license from USB consortium in order to get you
manufacturer ID code spans etc. And IIRC it was on the order of EURO
4-5K

If your inteface was a hard macro or built into a microcontroller, you
might be able to get an ID or two free of charge from the producer of
the chip, but without it you have to plunge the dough by yourself if you
want to sell the thing as USB compatible.

Ethernet MAC span is both cheaper and less neccessary.

I'll second the "USB is crap" comment.

If you must use USB2, I recommend using external PHY parts.

I know of three "standards" for interfacing controller chips to PHYs:
- UTMI+ (60MHz parallel)
- ULPI (60MHz parallel)
- HSIC (240MHz DDR)
You can buy PHY chips from Microchip (nee SMSC), TI, etc. I've only used
ULPI ones from SMSC.

BTW, there's a USB3.1 standard on the way, giving around 10Mb/s, with
5V / 2A power. It uses similar connections to USB3.0, but with different
signalling.

Regards,
Allan

 

[Brane2]

Dne ponedeljek, 05. maj 2014 16:57:24 UTC je oseba John Speth napisala:

I'll second the "USB is crap" comment.



What a strange comment. It is what it is, not perfect, but nothing is

perfect.

Crap is also not perfect, so no collision there.

You could say everything we do or use is crap if you don't

state why.

It would be far to tedious.

But in short - collective intelligence of its implementing body ranges from braindead to level of average moron.

Its standard haven't so much evolved as it caught tumor which has during the course of its growth simply eaten original intentions and implementation.

It's like one of those news we keep reading about "Doctors removed 100lb tumor".

Except that this patient haven't had the courage to go lie under scalpel yet.
When tumor overgrows you, "benign" means just that it prefers having you around as a carrier instead as food...

 

[John Speth]

> I'll second the "USB is crap" comment.

What a strange comment. It is what it is, not perfect, but nothing is
perfect. You could say everything we do or use is crap if you don't
state why.

USB is usually a requirement for implementers. For users it's a cheap
interface for connecting their gadgets. Think of all the revenue
generated for companies through the application of USB.

JJS

 

[Theo Markettos]

Allan Herriman <allanherriman@hotmail.com> wrote:
> I'll second the "USB is crap" comment.

It may be. But look at your FPGA. How do you connect it to your PC?
It might have ethernet or PCIe, but almost invariably what comes first is
USB.

> If you must use USB2, I recommend using external PHY parts.

This is the wrong solution because those chips are never there when you need
them. If you're doing your own board you can put on one, but many dev
boards don't have them. Then you need to program the PHY chip, and then you
need a softcore MAC on the FPGA. The FPGA vendors don't provide this for
free, so it's $30K to thirdparty vendors before you're started. And it'll
take you a very long time to get started because you need to understand it
first.

Meanwhile a USB2 microcontroller with flexible endpoint support is $6.
Why can't this functionality fit on an FPGA?

Why does every dev board have a dumb FTDI chip on it as a bridge to RS232 or
JTAG? Why isn't USB2 an FPGA programming option (in addition to JTAG)?
After all, plenty of consumer kit these days has USB2
reprogram/recovery/firmware update modes.

BTW, there's a USB3.1 standard on the way, giving around 10Mb/s, with
5V / 2A power. It uses similar connections to USB3.0, but with different
signalling.

Do you know if the signalling is more amenable to FPGA transceivers than
current USB2? I admit I haven't looked at the USB3.0 signalling standard
either. (It's at least not trying to drive wires bidirectionally).

Theo

 

[rickman]

On 5/5/2014 1:35 PM, Brane2 wrote:

Dne ponedeljek, 05. maj 2014 16:57:24 UTC je oseba John Speth napisala:
I'll second the "USB is crap" comment.



What a strange comment. It is what it is, not perfect, but nothing is

perfect.

Crap is also not perfect, so no collision there.


You could say everything we do or use is crap if you don't

state why.


It would be far to tedious.

But in short - collective intelligence of its implementing body ranges from braindead to level of average moron.

Its standard haven't so much evolved as it caught tumor which has during the course of its growth simply eaten original intentions and implementation.

It's like one of those news we keep reading about "Doctors removed 100lb tumor".

Except that this patient haven't had the courage to go lie under scalpel yet.
When tumor overgrows you, "benign" means just that it prefers having you around as a carrier instead as food...

Yes, that is much better. I understand perfectly what you don't like
about USB now. Thanks for the huge clarity in explanation...

Meanwhile the rest of us get on with our work using USB...

--

Rick

 

[Rob Doyle]

On 5/5/2014 1:40 PM, rickman wrote:

Yes, that is much better. I understand perfectly what you don't like
about USB now. Thanks for the huge clarity in explanation...

Meanwhile the rest of us get on with our work using USB...

Yup. It's the worst interface there is - except for the alternatives...

Rob.

 

[Adam GĂłrski]

W dniu 2014-05-04 17:02, Theo Markettos pisze:

I've been pondering...

When it comes to attaching an FPGA to a PC, there are lots of options.
First there's JTAG, then there's RS232, then there's ethernet, and PCIe.
But there's an elephant in this room: why is USB on FPGA so hard?

Sure, every FPGA can be connected to a PC with USB, but it's usually through
a dumb bridge chip that does RS232, or maybe uses USB to bitbang JTAG. USB2
is in 'easy' territory for FPGAs at 480Mbps, while USB3 5Gbps is the same
bitrate as PCIe Gen 2. Every PC made in the last 15 years has USB.
Meanwhile, being stuck behind a bridge chip we manage single-figures Mbps.

Now there are dev boards out there with USB PHY or USB MAC chips on them,
which is all very nice, but all very painful to program. Plus they're never
there when you need them. But why should this be necessary? Any $2 junk
gadget comes with a USB2 device interface these days - I don't know what fab
process they use, but it can't be too fancy. Likewise USB microcontrollers
are a few dollars.

I realise the USB stack isn't the most friendly to implementation on FPGA -
it doesn't play nicely with FPGA SERDES for example. But if a $2 gadget can
have all the functions of a USB device on an antique process node, why don't
modern FPGAs have at least native USB2 device mode?

Theo

Use first from the row FPGA SoC kit with linux on board.
Then you have not only FPGA but also almost standard ARM subsystem with
all ethernet, usb, rs232 and so on.
Typically you can start ready to use linux image from sd card.
This way you have solved problem with interfacing PC to fpga cause ARM
system has pretty wide access to FPGA resources.

Take a look here:
http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=167&No=816&PartNo=2


Adam

 

[KJ]

On Tuesday, May 6, 2014 9:17:25 AM UTC-4, Allan Herriman wrote:

USB isn't alone there - for example my current employer owns an Ethernet
OUI (a big block of MAC addresses) as well as an Ethertype (protocol
specifier). Both of those cost money, but it's a modest once-off cost
unlike the annual charge from USB-IF.

The annual charge is not mandatory, it is only to allow you to license use of their logos on new products. You can simply pay the first year (which gets you your VID) and never pay again. If having the USB logo is important to your product marketing, then you do have to pay for that privilege. Bottom line is that the first year $$ gets you the VID (and the use of logos if you choose); subsequent year's $$ allows you to continue to use logos.

Another thing to consider is that for (e.g.) Ethernet, there are MAC
addresses and Ethertypes that you can use for your hobby projects and
experimental protocols that won't get you into trouble. The USB-IF don't
provide VID / PID values intended for a similar purpose. (I understand
that if you buy a VID with the purpose of making it "free" they will come

A hobby project can use any VID since they do not need to worry about interoperability with anything that the hobbyist doesn't already know about. Providing something for 'free' takes it a bit outside of the realm of a strict 'hobby' which may open you up to folks coming after you as you say.

Kevin Jennings

 

[Allan Herriman]

On Tue, 06 May 2014 01:12:34 +0100, Theo Markettos wrote:

Allan Herriman <allanherriman@hotmail.com> wrote:
I'll second the "USB is crap" comment.

It may be.

I should clarify. I've made many boards over the years, using a variety
of interface standards. USB has never struck me as being elegant or
efficient. Its ubiquity, low cost (in volume), a robust connector and
power on the same cable as the signals seem to be its biggest plusses.

The USB physical layer isn't too bad, IMO. Most of the issues
encountered during development are to do with the (software) drivers.
That and the reuse of VID / PID values by cheap knock-off clone gizmos
that don't quite match the functionality of the original, yet are still
expected to work. (That isn't the fault of the USB standard though.)


Other posters mentioned the need to purchase an official VID / PID. The
process is too expensive for low volume or hobby projects.

USB isn't alone there - for example my current employer owns an Ethernet
OUI (a big block of MAC addresses) as well as an Ethertype (protocol
specifier). Both of those cost money, but it's a modest once-off cost
unlike the annual charge from USB-IF.
Another thing to consider is that for (e.g.) Ethernet, there are MAC
addresses and Ethertypes that you can use for your hobby projects and
experimental protocols that won't get you into trouble. The USB-IF don't
provide VID / PID values intended for a similar purpose. (I understand
that if you buy a VID with the purpose of making it "free" they will come
after you.)

But look at your FPGA. How do you connect it to your PC?
It might have ethernet or PCIe, but almost invariably what comes first
is USB.

It's the opposite for me. If one of my boards with an FPGA on it is
connecting to a PC, it'll be via Ethernet.

During debugging, I might rarely use USB to connect a JTAG pod to my PC
though.

If you must use USB2, I recommend using external PHY parts.

This is the wrong solution

I respectfully disagree. One thing that you might like to consider is
the I/O required for USB2. It matches well to the sort of process that
you would use for a $2 microcontroller, but not so well to the low
voltage I/O that you'd find on a 28nm FPGA.
There are also analog functions that are needed that you will not find on
an FPGA. FPGA vendors don't like including anything that doesn't have
wide applicability.

OTOH USB3 uses serial signalling that might be a good match for FPGA
transceivers. I haven't looked closely enough at the standard to know
for sure, but I suspect there will be problems with idle or sleep (or
something like that). OTOH, FPGA transceivers now have support for the
analog signalling for SATA, so if there's enough demand in the
marketplace, anything can happen.
I only put a USB3 controller into a product once - a (then new) NEC /
Renesas part that connected to my system using PCIe, so I can't claim to
be a USB3 expert.

I'm also aware that low speed (1.5Mb/s) USB can be bit-bashed in software
on a cheap microcontroller. I don't think it would be compliant with the
spec but it does seem to work and is extremely cheap.
That really sounds like it could easily fit into an FPGA, possibly with
the addition of some external level translators.

chips are never there when you
need them.

I know you're talking about boards, but if you were talking about part
availability, that would be a good point. USB is used in consumer
products, and this means that the parts sometimes have short production
lives.
Some years ago I designed a USB2 hub from ST-Ericcson into a product.
They had been made obsolete before our second production run. Now
there's an SMSC one in its place. Since then, SMSC has been bought by
Microchip and who knows what's going to happen.

Those issues can apply to any part on your board though, and aren't
unique to USB. (Has anyone tried to get DDR3 RAM chips when some company
in China is manufacturing a large batch of tablets?)

If you're doing your own board you can put on one, but many
dev boards don't have them.

I don't use dev boards, so I really shouldn't comment.

> Why isn't USB2 an FPGA programming option (in addition to JTAG)?

Substitute the string "PCIe" for "USB2" and you have a question I asked
of the local Altera and Xilinx reps about five years ago.

I'm still waiting for a good solution to that problem that doesn't
involve putting a "bootloader" NVM on the board to configure the FPGA
just so it can talk PCIe to get the rest of the configuration.

My guess: USB2 - never. USB3 - a very remote possibility.

Regards,
Allan

 

[Theo Markettos]

Allan Herriman <allanherriman@hotmail.com> wrote:

I should clarify. I've made many boards over the years, using a variety
of interface standards. USB has never struck me as being elegant or
efficient. Its ubiquity, low cost (in volume), a robust connector and
power on the same cable as the signals seem to be its biggest plusses.

I agree. It's the ubiquity that makes it really hard to ignore. (looks at
laptop: available ports are Thunderbolt - an obfuscated version of PCI
Express that's impossible for normal mortals to use[1] - and USB3.)

Other posters mentioned the need to purchase an official VID / PID. The
process is too expensive for low volume or hobby projects.

Presumably an FPGA could come with a default manufacturer VID/PID, which is
device class FF and has a higher level protocol for arbitrating
functionality. If you then want to sell it as a product that implements a
standard device class then you need apply for a VID/PID. But you have
flexibility to do other things (eg ship the first version of your product as
an FPGA, then switch to ASIC using the same driver and VID/PID code. Or
impersonate another device for interoperability).

It's the opposite for me. If one of my boards with an FPGA on it is
connecting to a PC, it'll be via Ethernet.

How do you program it? Do you have an onboard Ethernet to JTAG converter?

I respectfully disagree. One thing that you might like to consider is
the I/O required for USB2. It matches well to the sort of process that
you would use for a $2 microcontroller, but not so well to the low
voltage I/O that you'd find on a 28nm FPGA.

That sounds plausible. Except every phone SoC has a USB OTG port - and some
of those are 28nm and not exactly low performance.

There are also analog functions that are needed that you will not find on
an FPGA. FPGA vendors don't like including anything that doesn't have
wide applicability.

Looking at die shots, USB on the Tegra 2 takes up about 1% of die area on a
40nm process (couldn't find any labelled 28nm photos) - that's roughly
0.5mm2. I suppose that could be too high a price to pay, though I wonder
how hard PCIe compares? OTOH a USB hard core wouldn't necessarily have all
the features of Tegra's, because you'd want the backend of it to be in
configurable soft logic.

OTOH USB3 uses serial signalling that might be a good match for FPGA
transceivers. I haven't looked closely enough at the standard to know
for sure, but I suspect there will be problems with idle or sleep (or
something like that). OTOH, FPGA transceivers now have support for the
analog signalling for SATA, so if there's enough demand in the
marketplace, anything can happen.

That would be interesting.

Is USB3 generally more sane in your opinion?

I'm also aware that low speed (1.5Mb/s) USB can be bit-bashed in software
on a cheap microcontroller. I don't think it would be compliant with the
spec but it does seem to work and is extremely cheap.
That really sounds like it could easily fit into an FPGA, possibly with
the addition of some external level translators.

I've been wondering about that - is there a reference for the minimal spec
that needs to be implemented? It might be a nice way of stripping down USB
to something easier to understand. At least the FPGA shouldn't have the
timing awkwardness of microcontrollers.

I know you're talking about boards, but if you were talking about part
availability, that would be a good point. USB is used in consumer
products, and this means that the parts sometimes have short production
lives.
Those issues can apply to any part on your board though, and aren't
unique to USB. (Has anyone tried to get DDR3 RAM chips when some company
in China is manufacturing a large batch of tablets?)

BTDT, for very similar 'fun'...

Why isn't USB2 an FPGA programming option (in addition to JTAG)?

Substitute the string "PCIe" for "USB2" and you have a question I asked
of the local Altera and Xilinx reps about five years ago.

I'm still waiting for a good solution to that problem that doesn't
involve putting a "bootloader" NVM on the board to configure the FPGA
just so it can talk PCIe to get the rest of the configuration.

Likewise, I have similar bringup tedium.

Do any motherboards wire up the PCIe JTAG lines in a sensible manner?

> My guess: USB2 - never. USB3 - a very remote possibility.

I'm all in favour of shooting USB2 and moving on...

Theo

[1] I have evil plans in the Thunderbolt department...

 

[David Brown]

On 06/05/14 15:17, Allan Herriman wrote:

On Tue, 06 May 2014 01:12:34 +0100, Theo Markettos wrote:

Allan Herriman <allanherriman@hotmail.com> wrote:
I'll second the "USB is crap" comment.

It may be.

I should clarify. I've made many boards over the years, using a variety
of interface standards. USB has never struck me as being elegant or
efficient. Its ubiquity, low cost (in volume), a robust connector and
power on the same cable as the signals seem to be its biggest plusses.

The USB physical layer isn't too bad, IMO. Most of the issues
encountered during development are to do with the (software) drivers.
That and the reuse of VID / PID values by cheap knock-off clone gizmos
that don't quite match the functionality of the original, yet are still
expected to work. (That isn't the fault of the USB standard though.)

Drivers /can/ be a problem with USB, but they don't have to be.

If you need your device to integrate with the operating system (such as
happens for mice, printers, USB speakers, mass storage devices, etc.),
then it is easy if you can re-use existing standardised drivers (such as
the OS's own HID or MSD drivers). If you need to make your own
specialised drivers, then it is a tough job on Linux - you need to learn
the details of how USB works on the OS as well as the details for the
USB class you are implementing, and distributing the drivers can be a
challenge. On Windows, even if you understand everything and can do all
the windows driver development, it is still a nightmare of signing,
certification, etc.

But if your device only needs to talk to programs /you/ write, or
libraries/dlls/so's that /you/ write, then it is a lot easier. On
Linux, libusb lets your application have direct access to the endpoints
on your USB device - you have full control without any drivers in the
middle. Until a few years ago, it was still hard on Windows - but
someone helpfully ported libusb from Linux to Windows as WinUSB, and
with the simple installer "zadig" you can avoid almost all issues with
drivers on Windows too.

Other posters mentioned the need to purchase an official VID / PID. The
process is too expensive for low volume or hobby projects.

USB isn't alone there - for example my current employer owns an Ethernet
OUI (a big block of MAC addresses) as well as an Ethertype (protocol
specifier). Both of those cost money, but it's a modest once-off cost
unlike the annual charge from USB-IF.

The charge for a USB VID is one-off. The charge to use the USB logo,
trademarks, etc., is annual.

For a hobby project, there is no problem - pick a VID of a company you
would never use, or an unassigned VID, and use that. For any
professional product, the $2000 (IIRC) charge to buy a VID is annoying
but if you budget it as though it were a piece of development equipment,
it is not going to be an issue.

Another thing to consider is that for (e.g.) Ethernet, there are MAC
addresses and Ethertypes that you can use for your hobby projects and
experimental protocols that won't get you into trouble. The USB-IF don't
provide VID / PID values intended for a similar purpose. (I understand
that if you buy a VID with the purpose of making it "free" they will come
after you.)

But look at your FPGA. How do you connect it to your PC?
It might have ethernet or PCIe, but almost invariably what comes first
is USB.

It's the opposite for me. If one of my boards with an FPGA on it is
connecting to a PC, it'll be via Ethernet.

During debugging, I might rarely use USB to connect a JTAG pod to my PC
though.

If you must use USB2, I recommend using external PHY parts.

This is the wrong solution

I respectfully disagree. One thing that you might like to consider is
the I/O required for USB2. It matches well to the sort of process that
you would use for a $2 microcontroller, but not so well to the low
voltage I/O that you'd find on a 28nm FPGA.
There are also analog functions that are needed that you will not find on
an FPGA. FPGA vendors don't like including anything that doesn't have
wide applicability.

OTOH USB3 uses serial signalling that might be a good match for FPGA
transceivers. I haven't looked closely enough at the standard to know
for sure, but I suspect there will be problems with idle or sleep (or
something like that). OTOH, FPGA transceivers now have support for the
analog signalling for SATA, so if there's enough demand in the
marketplace, anything can happen.
I only put a USB3 controller into a product once - a (then new) NEC /
Renesas part that connected to my system using PCIe, so I can't claim to
be a USB3 expert.

I'm also aware that low speed (1.5Mb/s) USB can be bit-bashed in software
on a cheap microcontroller. I don't think it would be compliant with the
spec but it does seem to work and is extremely cheap.

Bit-banging low speed USB should be perfectly compliant with the specs
(if it is done right, of course). On an FPGA there should be no problem
implementing 12 Mb/s USB directly, or 480 Mb/s using an external PHY
(the XMOS devices do that, with the 480 Mb/s USB device running in
software). The USB protocol is not /that/ complicated.

That really sounds like it could easily fit into an FPGA, possibly with
the addition of some external level translators.

because those [PHY] chips are never there when you
need them.

I know you're talking about boards, but if you were talking about part
availability, that would be a good point. USB is used in consumer
products, and this means that the parts sometimes have short production
lives.
Some years ago I designed a USB2 hub from ST-Ericcson into a product.
They had been made obsolete before our second production run. Now
there's an SMSC one in its place. Since then, SMSC has been bought by
Microchip and who knows what's going to happen.

Those issues can apply to any part on your board though, and aren't
unique to USB. (Has anyone tried to get DDR3 RAM chips when some company
in China is manufacturing a large batch of tablets?)

If you're doing your own board you can put on one, but many
dev boards don't have them.

I don't use dev boards, so I really shouldn't comment.

Why isn't USB2 an FPGA programming option (in addition to JTAG)?

Substitute the string "PCIe" for "USB2" and you have a question I asked
of the local Altera and Xilinx reps about five years ago.

I'm still waiting for a good solution to that problem that doesn't
involve putting a "bootloader" NVM on the board to configure the FPGA
just so it can talk PCIe to get the rest of the configuration.

My guess: USB2 - never. USB3 - a very remote possibility.

Regards,
Allan

 

On Wednesday, May 7, 2014 2:38:26 AM UTC+3, Theo Markettos wrote:

Allan Herriman <allanherriman@hotmail.com> wrote:




I respectfully disagree. One thing that you might like to consider is
the I/O required for USB2. It matches well to the sort of process that
you would use for a $2 microcontroller, but not so well to the low
voltage I/O that you'd find on a 28nm FPGA.

That sounds plausible. Except every phone SoC has a USB OTG port - and some
of those are 28nm and not exactly low performance.

I'd guess that at least some of 28nm SOCs require external level-shifter. Actually I'd expect it to be true starting from 65nm.

Unfortunately, it's damn hard to get detailed datasheets for SOCs from Quallcomm, Mediatek, Apple or Samsung.

But we can take a look at USB controllers of Xilinx Zync, Altera Cyclon-V SE/SX/ST, Freescale i.MX 6 series and QorIQ and TI OMAP4 and OMAP5. They use virtually the same technology, but not as secretive as high-volume folks.
Both Altera and Xilinx export UTMI+ ULPI interface and need external PHY.
Both Freescale families implement PHY on chip.
TI OMAP4 needs external PHY.
TI OMAP5 implements both interface to external phy and on-chip USB 2/3 PHY. On chip PPY has few limitations, but they are probably irrelevant in your use case.

 

[John Miles]

On Tuesday, May 6, 2014 8:24:45 AM UTC-7, KJ wrote:

On Tuesday, May 6, 2014 9:17:25 AM UTC-4, Allan Herriman wrote:

USB isn't alone there - for example my current employer owns an Ethernet

OUI (a big block of MAC addresses) as well as an Ethertype (protocol

specifier). Both of those cost money, but it's a modest once-off cost

unlike the annual charge from USB-IF.





The annual charge is not mandatory, it is only to allow you to license use of their logos on new products. You can simply pay the first year (which gets you your VID) and never pay again. If having the USB logo is important to your product marketing, then you do have to pay for that privilege. Bottom line is that the first year $$ gets you the VID (and the use of logos if you choose); subsequent year's $$ allows you to continue to use logos.

If you don't care about logos, you can always license a subset of
VID 16D0 from MCS Electronics for around 10 Euros each. They bought their VID before the USB-IF cracked down on resellers.

http://www.mcselec.com/index.php?page=shop.product_details&flypage=shop..flypage&product_id=92&option=com_phpshop&Itemid=1

I'm not sure if this would keep you from getting WHQL certified or not, and I'd assume it would rule out your ability to use the official USB logo. But for many/most products, nobody gives much of a hoot about either of these.

-- john, KE5FX (no relationship with MCS other than as a satisfied customer)

 

Den tirsdag den 6. maj 2014 15.17.25 UTC+2 skrev Allan Herriman:

On Tue, 06 May 2014 01:12:34 +0100, Theo Markettos wrote:



Allan Herriman <allanherriman@hotmail.com> wrote:

I'll second the "USB is crap" comment.



It may be.



I should clarify. I've made many boards over the years, using a variety

of interface standards. USB has never struck me as being elegant or

efficient. Its ubiquity, low cost (in volume), a robust connector and

power on the same cable as the signals seem to be its biggest plusses.



The USB physical layer isn't too bad, IMO. Most of the issues

encountered during development are to do with the (software) drivers.

That and the reuse of VID / PID values by cheap knock-off clone gizmos

that don't quite match the functionality of the original, yet are still

expected to work. (That isn't the fault of the USB standard though.)





Other posters mentioned the need to purchase an official VID / PID. The

process is too expensive for low volume or hobby projects.



USB isn't alone there - for example my current employer owns an Ethernet

OUI (a big block of MAC addresses) as well as an Ethertype (protocol

specifier). Both of those cost money, but it's a modest once-off cost

unlike the annual charge from USB-IF.

Another thing to consider is that for (e.g.) Ethernet, there are MAC

addresses and Ethertypes that you can use for your hobby projects and

experimental protocols that won't get you into trouble. The USB-IF don't

provide VID / PID values intended for a similar purpose. (I understand

that if you buy a VID with the purpose of making it "free" they will come

after you.)



But look at your FPGA. How do you connect it to your PC?

It might have ethernet or PCIe, but almost invariably what comes first

is USB.



It's the opposite for me. If one of my boards with an FPGA on it is

connecting to a PC, it'll be via Ethernet.



During debugging, I might rarely use USB to connect a JTAG pod to my PC

though.



If you must use USB2, I recommend using external PHY parts.



This is the wrong solution



I respectfully disagree. One thing that you might like to consider is

the I/O required for USB2. It matches well to the sort of process that

you would use for a $2 microcontroller, but not so well to the low

voltage I/O that you'd find on a 28nm FPGA.

There are also analog functions that are needed that you will not find on

an FPGA. FPGA vendors don't like including anything that doesn't have

wide applicability.



OTOH USB3 uses serial signalling that might be a good match for FPGA

transceivers. I haven't looked closely enough at the standard to know

for sure, but I suspect there will be problems with idle or sleep (or

something like that). OTOH, FPGA transceivers now have support for the

analog signalling for SATA, so if there's enough demand in the

marketplace, anything can happen.

I only put a USB3 controller into a product once - a (then new) NEC /

Renesas part that connected to my system using PCIe, so I can't claim to

be a USB3 expert.



I'm also aware that low speed (1.5Mb/s) USB can be bit-bashed in software

on a cheap microcontroller. I don't think it would be compliant with the

spec but it does seem to work and is extremely cheap.

That really sounds like it could easily fit into an FPGA, possibly with

the addition of some external level translators.

I tried the opencores 12Mbit USB years ago, it was easy enough to get running

The design was intended to use a phy but I just used a bit of logic an a
differential input in parallel with two tristate outputs, it is all 3.3V


Doesn't even the latest and greatest FPGAs have some IOs capable of 3.3V?


480Mbit would be harder, doubt you just do 4x sampling to recover clock
like you can with 12Mbit

because those [PHY] chips are never there when you

need them.



I know you're talking about boards, but if you were talking about part

availability, that would be a good point. USB is used in consumer

products, and this means that the parts sometimes have short production

lives.

Some years ago I designed a USB2 hub from ST-Ericcson into a product.

They had been made obsolete before our second production run. Now

there's an SMSC one in its place. Since then, SMSC has been bought by

Microchip and who knows what's going to happen.



Those issues can apply to any part on your board though, and aren't

unique to USB. (Has anyone tried to get DDR3 RAM chips when some company

in China is manufacturing a large batch of tablets?)



If you're doing your own board you can put on one, but many

dev boards don't have them.



I don't use dev boards, so I really shouldn't comment.



Why isn't USB2 an FPGA programming option (in addition to JTAG)?



Substitute the string "PCIe" for "USB2" and you have a question I asked

of the local Altera and Xilinx reps about five years ago.



I'm still waiting for a good solution to that problem that doesn't

involve putting a "bootloader" NVM on the board to configure the FPGA

just so it can talk PCIe to get the rest of the configuration.



My guess: USB2 - never. USB3 - a very remote possibility.



Regards,

Allan

-Lasse

 

[Tim Wescott]

On Sun, 04 May 2014 12:50:28 -0700, Brane2 wrote:

Dne nedelja, 04. maj 2014 15:02:44 UTC je oseba Theo Markettos napisala:

SNIP

But there's an elephant in this room: why is USB on FPGA so hard?

First, USB is crap.

Second, you need license from USB consortium in order to get you
manufacturer ID code spans etc. And IIRC it was on the order of EURO
4-5K

If your inteface was a hard macro or built into a microcontroller, you
might be able to get an ID or two free of charge from the producer of
the chip, but without it you have to plunge the dough by yourself if you
want to sell the thing as USB compatible.

Ethernet MAC span is both cheaper and less neccessary.

If the customer wants USB, then USB is the right way to go.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com