Two different usb devices used at the same time, the rate be affected?

NTDEV
1

hi,my dear friend,now i have problem as follows:

now i have two usb device, a usb camera device,and a usb to serial GPS,when only use one of them,it run well.
but when use GPS,my camera device rate be affected,such as before the GPS device plug in,i can receive enough data (2M) per frame,but after plug in the usb to serial GPS ,the camera only receive about 1.6M data, but at this time ,the GPS only plug in ,and not tranfer data.
the problem also happen when the GPS tranfer data, at this time ,my camera also receive not enough data,and receive about 1.6M data.
who can help me ,Any help to be appreciated. thank you ,my friends.

2

Do you have a USB analyser? It will tell you why your GPS is reducing the bandwidth available to your camera.
A random guess is the GPS is using or reserving more bandwidth than you would expect for a simple stream of geo-location data.

Good luck,
Tim.

From: xxxxx@lists.osr.com [xxxxx@lists.osr.com] On Behalf Of zhonghong200@163.com [zhonghong200@163.com]
Sent: 11 November 2010 02:24
To: Windows System Software Devs Interest List
Subject: [ntdev] Two different usb devices used at the same time, the rate be affected?

hi,my dear friend,now i have problem as follows:

now i have two usb device, a usb camera device,and a usb to serial GPS,when only use one of them,it run well.
but when use GPS,my camera device rate be affected,such as before the GPS device plug in,i can receive enough data (2M) per frame,but after plug in the usb to serial GPS ,the camera only receive about 1.6M data, but at this time ,the GPS only plug in ,and not tranfer data.
the problem also happen when the GPS tranfer data, at this time ,my camera also receive not enough data,and receive about 1.6M data.
who can help me ,Any help to be appreciated. thank you ,my friends.

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3

thank you ,Tim Green

i don’t have a usb analyser,is there any other method to test the usb bandwidth ?such as through tools or software ,thank you.

another question, when use the two usb device in the PC of high Configuration ,it run well.
but when use int the PC of lower Configuration?the usb camera can not run well ?it can not receive enough data.

thank you, everyone.

4

zhonghong200@163.com wrote:

hi,my dear friend,now i have problem as follows:

now i have two usb device, a usb camera device,and a usb to serial GPS,when only use one of them,it run well.
but when use GPS,my camera device rate be affected,such as before the GPS device plug in,i can receive enough data (2M) per frame,but after plug in the usb to serial GPS ,the camera only receive about 1.6M data, but at this time ,the GPS only plug in ,and not tranfer data.
the problem also happen when the GPS tranfer data, at this time ,my camera also receive not enough data,and receive about 1.6M data.
who can help me ,Any help to be appreciated. thank you ,my friends.

As I recall, your camera uses a bulk pipe. That means you get whatever
bandwidth is left over, after all the other devices have made their
reservations. If your GPS device uses an interrupt pipe or an
isochronous pipe, it has a chunk of bandwidth reserved entirely for its
use, and that will limit the amount left over for you.

That’s why cameras use isochronous pipes. If there’s not enough
bandwidth, you know it as soon as the device is plugged in.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.

5

thank you Tim Roberts,

but when use the two usb device in the PC of high Configuration ,it run well,why? is the high configuration computer have more bandwidth than the lower configuration computer.thank you .

6

Do you mean Low Speed USB and High Speed USB? The first is 1.5Mb/s and the later is 480Mb/s, which would explain why it runs well in the latter and not so well in the former. Are you sure you don’t want to get a USB analyser? It would show you this and any other problems you might have on the line.

Tim.

From: xxxxx@lists.osr.com [xxxxx@lists.osr.com] On Behalf Of zhonghong200@163.com [zhonghong200@163.com]
Sent: 12 November 2010 01:12
To: Windows System Software Devs Interest List
Subject: RE:[ntdev] Two different usb devices used at the same time, the rate be affected?

thank you Tim Roberts,

but when use the two usb device in the PC of high Configuration ,it run well,why? is the high configuration computer have more bandwidth than the lower configuration computer.thank you .

NTDEV is sponsored by OSR

For our schedule of WDF, WDM, debugging and other seminars visit:
http://www.osr.com/seminars

To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer

7

thank you Tim Green,I mean my computer configuration ,and the same High Speed USB.

8

is there have a method to limit the usb Bandwidth?

9

zhonghong200@163.com wrote:

is there have a method to limit the usb Bandwidth?

If the devices use bulk pipes, they will compete for the bandwidth. The
host controller tries to be fair about it. If the devices use
isochronous pipes, then each device gets its reservation. Commonly,
isochronous devices will have a number of alternate settings with
various maximum packet sizes. If the driver fails when selecting the
maximum setting, it tries smaller and smaller settings until it succeeds.

–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.