| Author |
Message |
bo
Guest
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 Posted:
Wed Dec 08, 2004 8:44 pm Post subject:
Re: "Emulate" USB Host |
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A little of the topic of this thread---but since it's getting a lot of
attention...
I need to implement a USB host controller for an embedded system
running VxWorks on a Xilinx Virtex II pro FPGA. Can anyone here
recommend a good choice for the external host USB chip? (IP cores were
too $$$) and software drivers that will run it? (I'll be connected
various devices--HIDs, mass storage, video, etc on the bus).
I've been told to avoid Intel parts. Anyone have any experience or
recommendations would be more than appreciated! Currently am thinking
Cypress or Transmedia.....
Regards,
Bo |
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Dave Hansen
Guest
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| Posted:
Wed Dec 08, 2004 10:04 pm Post subject:
Re: "Emulate" USB Host |
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I hesitate to post this, because I don't want to seem to be carrying
USB's water. As I've said before, I don't have any particular
interest in USB...
On 7 Dec 2004 16:32:48 GMT, Hans-Bernhard Broeker
<broeker@physik.rwth-aachen.de> wrote:
| Quote: | Dave Hansen <iddw@hotmail.com> wrote:
On 7 Dec 2004 15:22:25 GMT, Hans-Bernhard Broeker
broeker@physik.rwth-aachen.de> wrote:
I've said this before, but I'll say this again: the only assumption
about motives that can really explain why USB was designed the way it
was designed, given existing technology at the time (particularly IEEE
1394, a.k.a. Firewire), is that it was predominantly a marketing
scheme to be able to keep selling powerful personal computers. It was
1394 and USB came along at pretty much the same time (though Apple had
FireWire earlier). If you're going to fault USB with overkill, how
much worse is 1394?
Not worse; but better, actually. 1394 is a well-done protocol,
fulfilling a real need (high-rate data streaming, esp. video), and it
does its job well.
I'm faulting USB for overkill for some of its applications only:
low-bandwidth, low-latency stuff like mouse and keyboard data has no
business occupying the same wire as a 11 Mb/s data stream. It's
|
So if I understand your position, you're not suggesting 1394 for
keyboards. And I'm not sure why you brought up 1394 at all.
Different bus for different applications. The only thing it really
has incommon with USB (AFAIK) is that they're both serial and both
self-configuring.
| Quote: | essentially impossible to avoid one type of communication getting into
the other's way. USB 1.1 is a complete hodgepodge. It's overkill for
|
Keyboard and mouse traffic doesn't really seem to get in anyone's way.
The only real problems I've heard of is when you try to listen to
music while burning a CD. USB 1.x can't keep up with it. Which is
one of the reasons there's USB 2.0 (which I haven't tried yet -- the
only USB peripheral on the new workstation the company bought for me
is the mouse).
| Quote: | some of its planned applications, and severely underpowered for most
of the others.
You'ld have thought that the guys at Intel & friends would know that
"one size fits all" doesn't ever really work. But they did it
nevertheless. Which begs the question: why?
|
I think it's less a matter of "one size fits all" than it is of
"adequate for projected uses." Capacity. Is it big enough?
Apparently the answer was no (isn't it usually?): Thus USB 2.0.
As to why, I think they've stated it pretty clearly. They wanted to
reduce hardware cost, and they wanted to simplify the end-user's job
of installing and removing peripherals. A USB controller is much
cheaper than the standard complement of 2 PS/2 ports, 1 or 2 serial
ports, a parallel port, and an ISA bus, software has essentially zero
manufacturing cost, and most users' CPU is idle 99.99% of the time.
And USB hot PnP actually _works_ (at least in my experience). So they
appear to have succeeded.
| Quote: |
a strategic move against the replacement of PCs by pervasive
computing.
I don't understand. Could you expand on this?
For a long time now, Microsoft and Intel have worked by the "single PC
as a center of your digital world" dogma. That's what led to crazy
stuff like the current typical supermarket PC: 3+ GHz CPU, a GiB of
memory, thermal design problems that make working in outer space
appear like a minor issue in comparison, PCs louder than your average
car, and all that.
|
I think Intel and Microsoft build what they think will sell. Their
game is to make money, not (necessarily) to innovate. If consumers
demand something other than the "single PC yada yada yada," then
they'll start building that.
| Quote: |
What we're looking at here is utter, total centralism. The same kind
of centralism is designed into almost every aspect of the USB
protocol. USB is highly asymmetric, offloading all the hard work to
the central hub: by silent assumption, that's a PC (of some kind,
i.e. Apple gets to play, too).
|
Agreed. But the idea is to reduce the cost of the peripheral. How
much do you want to pay for a basic keyboard? How successfull would
USB have been if the cost adder for the interface was, say, $10
instead of <$1? That would be seen as a conspiracy -- Intel foisting
expensive interface hardware on PC users, and attempting to extract a
huge slice of the money pie in the peripherals market.
Consider the situation of one of the projects I'm working on. Very
simple module, uses less than 2K program memory on a 14-bit PIC
microcontroller. A potential customer is looking at putting this
device on their vehicle network (CAN) to allow the body control
computer to enable or disable the device and to allow us to transmit
some diagnostic information. Suddenly we're looking at a 64K part
just to get the manufacturer-approved networking libraries loaded.
The customer is looking at simpler, more cost-effective solutions
now...
| Quote: |
Now it's commonly accepted that dogmatic centralism is wasteful.
Distributed systems are often more efficient, and it's a lot easier to
specialize from a distributed general design to a one-node case than
to generalize from a centralistic design to a situation where a single
center simply can't cut it.
|
I don't know where you get this. Distributed computing is _hard_.
Microsoft can't even get multithreading to work well, and the myriad
application vendors are worse.
You're upset because Intel and Microsoft didn't try to bootstrap an
entirely new personal computing paradigm?
| Quote: |
IMHO it's at least plausible to assume that in a purely open market,
without the Wintel monopoly, other players would have grabbed a
significant share of the market in the move from the single PC to a
world of computing power delivered at the exact point it's needed.
|
Oh, I see. You're upset because the new paradigm couldn't compete.
| Quote: |
To put it bluntly: there was *nothing* wrong with the PC keyboard
interface that it would have taken something like USB to fix. There
This is mostly true, but incomplete. USB is designed to replace the
keyboard, mouse, serial, and parallel ports as well as the ISA bus.
Wait a minute: a 11 Mbit/s star (it's not actually a bus), disturbed
|
Actually, I'd describe it as point-to-point. Hubs act as repeaters.
| Quote: | by high-priority 1.5Mbit/s packets and several layers of protocol
overhead is supposed to replace an 64 Mbit/s bus that was already
being stretched to its limis by hardware of that day? You gotta be
kidding.
If there's a single I/O interface of the legacy PC USB 1.1 was in no
way fit to replace, it's the ISA bus.
|
In practice, it's not that bad. In fact, keyfob flash drives are
kinda slick. To replicate that functionality with ISA, you need to
install a flash card adapter ($ and compatibility issues), and 1394
would probably not be as cost-effective.
When bandwidth requirements exceeded ISA'a capability, we got PCI. By
the time USB came around, ISA bandwidth wasn't really an issue. USB
is perfectly capable of handling any single peripheral that would
normally be attached to the ISA. It's only when you start running a
couple (or more) high-bandwidth processes at the same time that you
run into trouble.
When a USB device is enumerated, it allocates bandwidth. In theory,
you should not be able to attach a device to the USB if its required
bandwidth would exceed that available (remaining) on the bus. Except
isochronous devices, which say "I'll take whatever is left over at any
given time. Obviously, it's the isochronous services that suffer when
bandwidth usage gets high -- usually sound devices.
| Quote: |
ISA PnP never worked very well.
That's what rightly got us PCI. Not an entirely sweet pill, either,
but in a totally different league than USB.
|
PCI is another technology that has been decried as a conspiracy to
prevent embedded systems designers from doing their job. In this case
the complexity resides more heavily in the hardware rather thn the
software side. How much harder is it to design a PCI card than an
ISA? How many PCI slots does your system have? Software is not that
much more difficult on PCI than ISA...
Regards,
-=Dave
--
Change is inevitable, progress is not. |
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Hans-Bernhard Broeker
Guest
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| Posted:
Wed Dec 08, 2004 11:21 pm Post subject:
Re: "Emulate" USB Host |
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|
Dave Hansen <iddw@hotmail.com> wrote:
[...]
| Quote: | I'm faulting USB for overkill for some of its applications only:
low-bandwidth, low-latency stuff like mouse and keyboard data has no
business occupying the same wire as a 11 Mb/s data stream. It's
So if I understand your position, you're not suggesting 1394 for
keyboards.
|
I'm not. That would make even less sense than a keyboard attached to
the same wire as a 320 GB external USB 2.0 hard disk.
| Quote: | And I'm not sure why you brought up 1394 at all.
|
Because USB devices fall into several large categories:
1) replacement of former "legacy" ports (keyboard, mouse, printer, modem, ...)
2) high-bandwidth devices (nowadays usually USB-2.0 hi-speed), like
external harddisks and video stuff.
3) stupid stuff, including USB-to-USB "network cables".
My point, is that 1) and 2) don't have any business travelling over
the same pair of wires, and for 2), defining a new protocol was
completely superfluous already when USB was originally designed ---
1394 filled that niche nicely, at higher bandwidth, with less hassle.
If they had designed a new bus for category 1), and 1) alone, that'd
have been perfectly fine with me. But by forcing category 2) into the
same channel, without compelling need of doing so, they crossed the
line.
| Quote: | Different bus for different applications. The only thing it really
has incommon with USB (AFAIK) is that they're both serial and both
self-configuring.
|
One difference that makes me criticize USB is that its
self-configuration mechanism is *way* over-complicated. It's this
mechanism, mainly, that causes the need for a PC at the root of the
tree. 1394 auto-configuration is so simple that a digical camcorder's
firmware can usually get it right without breaking a sweat.
| Quote: | essentially impossible to avoid one type of communication getting into
the other's way.
Keyboard and mouse traffic doesn't really seem to get in anyone's way.
|
Well, at the heart of it, HID data are sent a USB transfer mode that
has them get priority over all high-rate user data on the same bus.
Add that HID devices are typically low-speed, and you have each byte
of mouse data bulldozing 10 or more bytes of other data out of the
way. With USB-2.0, make that ~300 bytes.
This design is a bit like building a single-lane highway to be used
jointly by cars and trucks, and then later declaring it good for
simultaneous use by Formula-1, too.
| Quote: | The only real problems I've heard of is when you try to listen to
music while burning a CD. USB 1.x can't keep up with it.
|
USB 1.x can no longer keep up with CD burning anyway, these days. Not
since the last 16x burners stopped being produced.
| Quote: | A USB controller is much cheaper than the standard complement of 2
PS/2 ports, 1 or 2 serial ports, a parallel port, and an ISA bus,
|
Except that one USB controller was apparently insufficient -- current
motherboard trend appears to be to move up from 6 to 8 onboard USB
ports --- yes, that's more than the overall number of ports on a
typical legacy PC, which USB set out to repeat by a single plug.
Doesn't seem to have worked out all that well, does it?
| Quote: | software has essentially zero manufacturing cost, and most users'
CPU is idle 99.99% of the time. And USB hot PnP actually _works_
(at least in my experience).
|
Let's say: it *can* work --- ISA PnP never stood a chance. Arguably
they shouldn't even have tried that. The major difference now is that
instead of hardware that doesn't have enough flexibility to work in
somewhat strange PCs, you now get software that doesn't work in
somewhat strange PCs.
Hot PnP? You tell that to the software of my USB scanner, which a)
complains loudly each time I boot without the scanner attached, b)
doesn't work at all if I plug in the scanner later, and c) reliably
brings down my Linux system if I so much as plug it in.
| Quote: | Agreed. But the idea is to reduce the cost of the peripheral. How
much do you want to pay for a basic keyboard?
|
Why should I have to pay *anything* extra for a basic keyboard, just
so it can coexist on a shared cable with my video camera, printer and
external harddisk? I think I shouldn't, because it shouldn't have to
do that. That's where the fundamental misconception is.
Reducing the number of different port types and plugs of a typical PC
was a good first idea. It started to gown-hill when somebody decided
that it must be reduced all the way to _one_ type of port.
| Quote: | Now it's commonly accepted that dogmatic centralism is wasteful.
Distributed systems are often more efficient, and it's a lot easier to
specialize from a distributed general design to a one-node case than
to generalize from a centralistic design to a situation where a single
center simply can't cut it.
I don't know where you get this. Distributed computing is _hard_.
|
I said it was *efficient*, not that it's easy. The telltale figure is
those '99.99% of the time idle' you quoted yourself: that's an
overgrown centralistic system, scaled to be powerful enough to do
everything and then some all by itself, which doesn't actually get any
work to do.
| Quote: | You're upset because Intel and Microsoft didn't try to bootstrap an
entirely new personal computing paradigm?
|
No. Because they (ab)used their effective control over the market to
keep the general public from recognizing that less centralistic
alternatives were even possible.
| Quote: | Oh, I see. You're upset because the new paradigm couldn't compete.
|
No. Because it wasn't given a fair chance to compete. Microsoft
decreed that a PC without USB was, effectively, unsellable. So
peripherals that aren't USB became effectively unsellable some time
after that.
| Quote: | If there's a single I/O interface of the legacy PC USB 1.1 was in no
way fit to replace, it's the ISA bus.
In practice, it's not that bad. In fact, keyfob flash drives are
kinda slick.
|
Yeah, but even they are bottlenecked by USB 1.1, so the good ones
are 2.0 these days.
But "replacing ISA bus" would have meant to take over the interface to
the main ISA bus device of a legacy PC, though: the internal harddisk.
And that's been faster than USB1.1's 11 Mbit/s for years before the
first USB mainboard was sold.
ISA bus has never really been much of an external interface anyway, so
I highly doubt replacing it was ever, actually, part of the design
goals of USB. If it had been, USB 1.1 would have been rated a
complete failure even by its authors.
USB keyfobs are slick mainly by comparison to what was lacking for
such a long time: a random-access, exchangeable storage medium with
significantly more capacity than a floppy disk, found in essentially
every PC. People got used to waiting for their CD burners to finish
working, instead.
| Quote: | When bandwidth requirements exceeded ISA'a capability, we got PCI. By
the time USB came around, ISA bandwidth wasn't really an issue.
|
Oh, ISA _bandwidth_ was very much an issue --- such a huge issue, in
fact, that it the only viable solution to it was to get rid of ISA bus
completely. ISA bus as such stopped to be an issue at that point, but
its bandwidth didn't.
| Quote: | USB is perfectly capable of handling any single peripheral that
would normally be attached to the ISA.
|
USB-2.0: yes. USB-1.1 was too slow by almost a factor of 10. Hard
disks have been faster than 1.5 MB/s continuous transfer rate for a
*long* time now.
--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain. |
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René
Guest
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| Posted:
Thu Dec 09, 2004 3:18 am Post subject:
Re: "Emulate" USB Host |
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|
"Hans-Bernhard Broeker" <broeker@physik.rwth-aachen.de> schreef in bericht
news:31ov16F3du2iuU1@news.dfncis.de...
| Quote: | Dave Hansen <iddw@hotmail.com> wrote:
On 7 Dec 2004 16:32:48 GMT, Hans-Bernhard Broeker
broeker@physik.rwth-aachen.de> wrote:
[...]
I'm faulting USB for overkill for some of its applications only:
low-bandwidth, low-latency stuff like mouse and keyboard data has no
business occupying the same wire as a 11 Mb/s data stream. It's
So if I understand your position, you're not suggesting 1394 for
keyboards.
I'm not. That would make even less sense than a keyboard attached to
the same wire as a 320 GB external USB 2.0 hard disk.
And I'm not sure why you brought up 1394 at all.
Because USB devices fall into several large categories:
1) replacement of former "legacy" ports (keyboard, mouse, printer, modem,
....)
2) high-bandwidth devices (nowadays usually USB-2.0 hi-speed), like
external harddisks and video stuff.
3) stupid stuff, including USB-to-USB "network cables".
My point, is that 1) and 2) don't have any business travelling over
the same pair of wires, and for 2), defining a new protocol was
completely superfluous already when USB was originally designed ---
1394 filled that niche nicely, at higher bandwidth, with less hassle.
|
Yes, but the big problem there was, if I recall correctly, that a license
fee (English is not my mother tongue, so I may be using the wrong word, I
mean that someone has patented something and other people who wish to use it
have to pay money to the patent holder) had to be payed of about 15$ for
every fw port on any device. I have always thought that this was the initial
reason why USB was developed by the people who didn't feel like paying that
money but who unfortunately turned out to be far less handy than the people
who invented fw (it was Apple, wasn't it).
For everybody who thinks that USB is a problem-solving thing and will make
PnP work all the time, just look at www.usbman.org . I have had so many
problems with external harddrives and many other people have. Even many
chipsets, like the ones from Ali, just don't work OK. I will always choose
firewire if I have the possibility.
Greetings,
Rene |
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CBFalconer
Guest
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| Posted:
Thu Dec 09, 2004 6:44 am Post subject:
Re: "Emulate" USB Host |
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Dave Hansen wrote:
| Quote: |
.... snip ...
If there's a single I/O interface of the legacy PC USB 1.1 was
in no way fit to replace, it's the ISA bus.
In practice, it's not that bad. In fact, keyfob flash drives are
kinda slick. To replicate that functionality with ISA, you need
to install a flash card adapter ($ and compatibility issues), and
1394 would probably not be as cost-effective.
|
Some years ago I built an extremely cheap peripheral. It's only
duty was to read a memory dump from a (nuclear) pulse height
analyzer, which in turn was in a peculiar ad-hoc format which
sufficed to dump and reload the PHA. The physical interface
consisted of the same miniature tape deck as was mounted in the
PHA, and a single CMOS buffer chip, all hung off the parallel port.
x86 timed loops did the clock/data separation, detected end of
record gaps, etc., and allowed the memory dumps to be transferred
to the PC and displayed and/or analyzed. It was profitable because
it cost almost NIL to manufacture, and the design effort was in the
software.
I am sure I was not alone in doing these things. None of this
would be possible with a USB interface.
--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address! |
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Meindert Sprang
Guest
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| Posted:
Thu Dec 09, 2004 11:09 am Post subject:
Re: "Emulate" USB Host |
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|
"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:41B77778.9AB9A875@yahoo.com...
| Quote: | Some years ago I built an extremely cheap peripheral. It's only
duty was to read a memory dump from a (nuclear) pulse height
analyzer, which in turn was in a peculiar ad-hoc format which
sufficed to dump and reload the PHA. The physical interface
consisted of the same miniature tape deck as was mounted in the
PHA, and a single CMOS buffer chip, all hung off the parallel port.
x86 timed loops did the clock/data separation, detected end of
record gaps, etc., and allowed the memory dumps to be transferred
to the PC and displayed and/or analyzed. It was profitable because
it cost almost NIL to manufacture, and the design effort was in the
software.
I am sure I was not alone in doing these things. None of this
would be possible with a USB interface.
|
Funny enough, the FTDI FT2232C chip is exactly designed to do this. Besides
the standard asynchronous protocol, it can also do synchronous protocols,
specially targeted to ISP and JTAG stuff.
Meindert |
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Ulf Samuelsson
Guest
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| Posted:
Thu Dec 09, 2004 2:22 pm Post subject:
Re: "Emulate" USB Host |
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| Quote: | I need to implement a USB host controller for an embedded system
running VxWorks on a Xilinx Virtex II pro FPGA. Can anyone here
recommend a good choice for the external host USB chip? (IP cores were
too $$$) and software drivers that will run it? (I'll be connected
various devices--HIDs, mass storage, video, etc on the bus).
Regards,
Bo
|
Does the Virtex contains a PowerPC?
Then the AT43USB380 might be what you want.
Will support Mass Storage and HID at least.
Don't know about Video.
The advantage of the AT43USB380 is that the Host S/W is simplified a lot.
The Host Stack is running on the chip, and the Virtex runs the Profiles.
Atmel delivers precompiled libraries for certain cores.
If it is not a Power PC, then further discussion is needed.
--
Best Regards
Ulf at atmel dot com
These comments are intended to be my own opinion and they
may, or may not be shared by my employer, Atmel Sweden. |
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Ulf Samuelsson
Guest
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| Posted:
Thu Dec 09, 2004 2:34 pm Post subject:
Re: "Emulate" USB Host |
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| Quote: | I'm not. That would make even less sense than a keyboard attached to
the same wire as a 320 GB external USB 2.0 hard disk.
And I'm not sure why you brought up 1394 at all.
Because USB devices fall into several large categories:
1) replacement of former "legacy" ports (keyboard, mouse, printer, modem,
....)
2) high-bandwidth devices (nowadays usually USB-2.0 hi-speed), like
external harddisks and video stuff.
3) stupid stuff, including USB-to-USB "network cables".
My point, is that 1) and 2) don't have any business travelling over
the same pair of wires, and for 2), defining a new protocol was
completely superfluous already when USB was originally designed ---
1394 filled that niche nicely, at higher bandwidth, with less hassle.
|
There are "political" issues here. P.1394 contains IP owned by Apple.
Intel was not exactly interested in promoting that, so they defined USB.
You may or may not like this, but I think Intel won.
I dont recall ever using my P.1394 mainly because no home electronics seems
to use it.
If my DVD Video provided P.1394 output from the TV Tuner, I would use it.
Don't own a DV camera which seems to be the only reason to use it at this
time.
I rather have multiple ports of of the same kind, than one or two of each,
since this gives me more flexibility.
Since I need USB ports for the Mouse, that means USB for everything.
I could get a P.1394 hard disk, but that would limit my options, and I don't
really
care too much about the speed on that one. With USB I can connect to more of
*my* home
equipment
--
Best Regards
Ulf at atmel dot com
These comments are intended to be my own opinion and they
may, or may not be shared by my employer, Atmel Sweden. |
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Antonio Pasini
Guest
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| Posted:
Fri Dec 10, 2004 2:56 am Post subject:
Re: "Emulate" USB Host |
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| Quote: | I need to implement a USB host controller for an embedded system
running VxWorks on a Xilinx Virtex II pro FPGA. Can anyone here
recommend a good choice for the external host USB chip? (IP cores were
too $$$) and software drivers that will run it? (I'll be connected
various devices--HIDs, mass storage, video, etc on the bus).
|
If you need HS operation, and don't have a PCI local bus, check Philips
parts:
onTheGo:
http://www.semiconductors.com/markets/connectivity/wired/usb/products/otg/isp1761/
host only:
http://www.semiconductors.com/markets/connectivity/wired/usb/products/host/isp1760/
Unfortunately, FlexStack source costs about $50K.
There's a PCI board with 1761, with a evaluation software for Linux. I do
not know if it comes with source for Linux, also.
Availability could be an issue for both, also (I suppose)...
They have also many full speed hosts. |
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Tom
Guest
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| Posted:
Wed Jan 05, 2005 4:38 am Post subject:
Re: "Emulate" USB Host |
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|
"Hans-Bernhard Broeker" <broeker@physik.rwth-aachen.de> wrote in message news:31ov16F3du2iuU1@news.dfncis.de...
| Quote: | 1) replacement of former "legacy" ports (keyboard, mouse, printer, modem, ...)
2) high-bandwidth devices (nowadays usually USB-2.0 hi-speed), like
external harddisks and video stuff.
3) stupid stuff, including USB-to-USB "network cables".
My point, is that 1) and 2) don't have any business travelling over
the same pair of wires, and for 2), defining a new protocol was
completely superfluous already when USB was originally designed ---
1394 filled that niche nicely, at higher bandwidth, with less hassle.
|
I get the impression that USB was originally designed to work like ADB
on Macs - i.e. for 1). The HID stuff is pretty neat, you can use a tool to
generate the HID class descriptor, and burn it into the Rom of a low cost
microcontroller with a low speed USB transceiver. Sure the driver on the
PC is probably a nightmare internally, but that only needs to be done once
per OS.
| Quote: |
If they had designed a new bus for category 1), and 1) alone, that'd
have been perfectly fine with me. But by forcing category 2) into the
same channel, without compelling need of doing so, they crossed the
line.
One difference that makes me criticize USB is that its
self-configuration mechanism is *way* over-complicated. It's this
mechanism, mainly, that causes the need for a PC at the root of the
tree. 1394 auto-configuration is so simple that a digical camcorder's
firmware can usually get it right without breaking a sweat.
|
Yeah, but the complication is on the host side, not on the device. The
device needs to be able to handle IIRC
Get Device Descriptor - fetch n bytes from Rom
Set Address - write a byte to a USB control reg
Set Configuration - the device probably only has one config, so it's a NOP.
You could light a led or something though, since it means that you are recognised
by the host.
plus read/write from/to whatever endpoints it needs for it's internal stuff.
Handling string descriptors would be nice, but you don't need it.
If you have a microcontroller with built in USB, all this is fairly painless -it's
easy to get it into a small rom.
| Quote: |
USB-2.0: yes. USB-1.1 was too slow by almost a factor of 10. Hard
disks have been faster than 1.5 MB/s continuous transfer rate for a
*long* time now.
|
USB key fobs are useful even with USB 1.0 actually, you can just leave stuff
copying while you do something else. But you're right that USB 1.0 isn't
exactly ideal for this sort of thing.
| Quote: |
--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain. |
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