TUSB8044A: What's the relationship between upstream port and downstream port.

Jason Ciou

Part Number: TUSB8044A

Hi team,

My customer would like to know.

What's the relationship between upstream port and downstream port.

the downstream port signal "is totally copied" from upstream port. Or will there be a little bit of retooling for downstream?

They want TI to confirm this one. could you please check that, thanks.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 317370 points

Yes, packets to/from downstream devices are not changed by the hub. (Except for the transaction translator that allows to speak a high-speed host with low-speed devices.)

For low/high speed, packets from the upstream port are broadcast to all downstream ports. (Devices ignore packets with the wrong address.) Packets from downstream ports are simply transmitted upstream; the host manages when devices are allowed to send packets.

For super speed, hubs work as switches and route packets only to the actually addressed downstream device.

In all cases, the host is connected to the upstream port, and controls the hub.

0 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Clemens,

Thanks for your explanation.

So the downstream port signal "is totally copied" from upstream port"?

Jason

0 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Clemens,

Because Hub's down stream port packets is from hub's upstream stream port.

they would like to know, are the packets of Hub's down stream port same as hub's upstream stream port?

or they are not totally same?

Jason

0 Clemens Ladisch over 3 years ago in reply to Jason Ciou

Guru 317370 points

Yes, retransmitted packets are identical.

(Why is this important?)

0 Jason Ciou over 3 years ago in reply to Clemens Ladisch

TI__Expert 3600 points

Hi Clemens,

Because my customer run into some issue, they want TI confirm the packets are identical, there is no any different.

Jason

0 JMMN over 3 years ago in reply to Jason Ciou

TI__Guru 60870 points

Hi Jason,

The information in the packets is the same, but the upstream and downstream packets are not identical. A USB 2.0 packet will have changes in the SYNC field and the EOP width when passed through a hub. In USB 3.0, the upstream port and downstream port of the hub can be in different power states. What is the customer issue?

Regards,

JMMN

0 Jason Ciou over 3 years ago in reply to JMMN

TI__Expert 3600 points

HI JMMN,

I am not very sure why they are asking that.

A USB 2.0 packet will have changes in the SYNC field and the EOP width when passed through a hub. => how to make sure the information is the same, when A USB 2.0 packet will have changes in the SYNC field and the EOP width. This behavior is normal? or this is come from USB spec.

In USB 3.0, the upstream port and downstream port of the hub can be in different power states. => what does this mean.

Jason

+1 JMMN over 3 years ago in reply to Jason Ciou

TI__Guru 60870 points

Hi Jason,

This is all expected behavior for hubs as defined in the USB specifications.

Regards,

JMMN

0 Jason Ciou over 3 years ago in reply to JMMN

TI__Expert 3600 points

Hi JMMN,

Thanks,

Jason

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TUSB8044A: What's the relationship between upstream port and downstream port.