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Guest
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 Posted: Fri Oct 17, 2008 2:04 pm Post subject: USB BUS capable of Bus Mastering |
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Hello folks ,
Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86
systems .
thanks
subra |
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Joe Pfeiffer
Guest
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| Posted: Fri Oct 17, 2008 9:17 pm Post subject: Re: USB BUS capable of Bus Mastering |
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avsrk67@yahoo.com writes:
| Quote: |
Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86
systems .
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No. |
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Rob Warnock
Guest
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| Posted: Sat Oct 18, 2008 4:52 pm Post subject: Re: USB BUS capable of Bus Mastering |
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Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
+---------------
| avsrk67@yahoo.com writes:
| > Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86 systems.
|
| No.
+---------------
Well, that's *almost* true. It certainly was true for USB 1.x devices.
But there's this new supplement to the USB 2.0 Spec called the
"On-The-Go" protocol (USB OTG) that lets slaves sometimes act
as masters:
http://en.wikipedia.org/wiki/USB_On-The-Go
It's intended for devices that are normally slaves to a host computer
to be able to talk directly to each other, e.g., a camera dumping a
picture directly to a printer with no computer available, etc.
But even with USB OTG [which *only* supports two-device point-to-point],
one of the devices is a master and the other a slave, although in
certain restricted cases the devices can swap roles dynamically.
[The Wikipedia article gives more detail about this aspect.]
-Rob
-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607 |
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Joe Pfeiffer
Guest
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| Posted: Sat Oct 18, 2008 9:19 pm Post subject: Re: USB BUS capable of Bus Mastering |
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rpw3@rpw3.org (Rob Warnock) writes:
| Quote: | Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
+---------------
| avsrk67@yahoo.com writes:
| > Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86 systems.
|
| No.
+---------------
Well, that's *almost* true. It certainly was true for USB 1.x devices.
But there's this new supplement to the USB 2.0 Spec called the
"On-The-Go" protocol (USB OTG) that lets slaves sometimes act
as masters:
|
Yes, I'm familiar with OTG. It isn't doing bus mastering like on a
PCI bus, as originally asked. |
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Guest
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| Posted: Sun Oct 19, 2008 12:52 pm Post subject: Re: USB BUS capable of Bus Mastering |
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Thank you Folks for the answer i had only a USB 1.1 capable device ,
in a hard way i learn't that it cannot do bus mastering .
That is by actually trying to use one in our app.
PCI devices work good .
Thanks
subra
On Oct 19, 6:32 am, r...@rpw3.org (Rob Warnock) wrote:
| Quote: | Joe Pfeiffer <pfeif...@cs.nmsu.edu> wrote:
+---------------
| r...@rpw3.org (Rob Warnock) writes:
| > Joe Pfeiffer <pfeif...@cs.nmsu.edu> wrote:
| > +---------------
| > | avsr...@yahoo.com writes:
| > | > Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86 systems.
| > |
| > | No.
| > +---------------
|
| > Well, that's *almost* true. It certainly was true for USB 1.x devices..
| > But there's this new supplement to the USB 2.0 Spec called the
| > "On-The-Go" protocol (USB OTG) that lets slaves sometimes act
| > as masters:
|
| Yes, I'm familiar with OTG. It isn't doing bus mastering like on a
| PCI bus, as originally asked.
+---------------
True. I was just trying to provide the closest approximate solution
to a very liberal interpretation of the original question.
Maybe I should have phrased it differently: "It won't do what you
actually asked for, <avsr...@yahoo.com>, but it'll do this other
thing that might be close enough for whatever you really want to do"
(which he didn't bother to tell us).
-Rob
-----
Rob Warnock <r...@rpw3.org
627 26th Avenue <URL:http://rpw3.org/
San Mateo, CA 94403 (650)572-2607 |
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Rob Warnock
Guest
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| Posted: Sun Oct 19, 2008 3:32 pm Post subject: Re: USB BUS capable of Bus Mastering |
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Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
+---------------
| rpw3@rpw3.org (Rob Warnock) writes:
| > Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
| > +---------------
| > | avsrk67@yahoo.com writes:
| > | > Is USB Bus capable of Bus Mastering (DMA ) like PCI Bus on x86 systems.
| > |
| > | No.
| > +---------------
| >
| > Well, that's *almost* true. It certainly was true for USB 1.x devices.
| > But there's this new supplement to the USB 2.0 Spec called the
| > "On-The-Go" protocol (USB OTG) that lets slaves sometimes act
| > as masters:
|
| Yes, I'm familiar with OTG. It isn't doing bus mastering like on a
| PCI bus, as originally asked.
+---------------
True. I was just trying to provide the closest approximate solution
to a very liberal interpretation of the original question.
Maybe I should have phrased it differently: "It won't do what you
actually asked for, <avsrk67@yahoo.com>, but it'll do this other
thing that might be close enough for whatever you really want to do"
(which he didn't bother to tell us).
-Rob
-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607 |
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