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USB superspeed peripherals Forum Discussions

rossi
Level 3
Level 3
25 sign-ins First solution authored 10 replies posted

Hi, 

My UVC video reference is running at 640x480 30fps. In this case, within my understanding the bitrate is calculated as below.

640 x 480 x 16(2bytes per pixel) x 30(fps) = 147,456,000 bps = 147.456Mbps

Then, what is the maximum bitrate of isochronous endpoint running on usb2.0/3.0? It would be great if I can have a simple formula like the above.

 

Regards,

Rossi

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1 Solution
Bakal
Moderator
Moderator
Moderator
50 sign-ins 10 solutions authored 25 replies posted

Hello Rossi,

A SuperSpeed isochronous transfer type can move up to 1024 x 16 x 3 bytes per service interval. Taking the minimum service interval as 125 µs, the maximum theoretical bandwidth for SuperSpeed isochronous transfer can be calculated as (maximum packet size * burst size * number of iso-packets / service interval). That works out to 1024 x 16 x 3 / 125µ bytes/s or 375 Mbps (3 Gb/s). 

Please refer to AN86947 Application note to know more about Isochronous Transfers.

Thanks,
Sakshi Bakal.

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Bakal
Moderator
Moderator
Moderator
50 sign-ins 10 solutions authored 25 replies posted

Hello Rossi,

A SuperSpeed isochronous transfer type can move up to 1024 x 16 x 3 bytes per service interval. Taking the minimum service interval as 125 µs, the maximum theoretical bandwidth for SuperSpeed isochronous transfer can be calculated as (maximum packet size * burst size * number of iso-packets / service interval). That works out to 1024 x 16 x 3 / 125µ bytes/s or 375 Mbps (3 Gb/s). 

Please refer to AN86947 Application note to know more about Isochronous Transfers.

Thanks,
Sakshi Bakal.

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rossi
Level 3
Level 3
25 sign-ins First solution authored 10 replies posted

Thank you Bakal

By the way, I'm more interested in USB2.0 because my environment doesn't allow me to use USB3.0.

So, I'm still curious about the maximum bitrate in USB2.0 on isochronous endpoint.

 

Regards,

Rossi

 

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Bakal
Moderator
Moderator
Moderator
50 sign-ins 10 solutions authored 25 replies posted

Hello,

Will you please let us know what speed you will be using in USB 2.0  high speed or low speed?  As both have different maximum bitrates on the isochronous endpoint.

Regards,
Sakshi Bakal

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rossi
Level 3
Level 3
25 sign-ins First solution authored 10 replies posted

Hello, 

USB 2.0 high speed, what I'm interested in.

Regards,

Rossi

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Bakal
Moderator
Moderator
Moderator
50 sign-ins 10 solutions authored 25 replies posted

Hello,

In high-speed mode, up to three isochronous packets can be transferred per endpoint, per micro-frame. In full-speed mode, only one isochronous packet can be transferred per endpoint, per frame. Other things are similar to superspeed.

Regards,
Sakshi Bakal

 

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