Level 3
Level 3

# FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

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

1 Solution
Moderator
Moderator

# Re: FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

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.

5 Replies
Moderator
Moderator

# Re: FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

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.

Level 3
Level 3

# Re: FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

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

Moderator
Moderator

# Re: FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

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

Level 3
Level 3

# Re: FX3 maximum bitrate of isochronous endpoint in USB2.0, 3.0

Hello,

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

Regards,

Rossi

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Moderator