Author Topic: Questions on USB protocol  (Read 4634 times)

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Offline promach

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Re: Questions on USB protocol
« Reply #50 on: November 02, 2021, 03:44:42 am »
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When a port determines that the locally-inserted plug is flipped (i.e. CC1 is open, CC2 is terminated), the USB4 Specification (reference Sideband Channel Lane Reversal) dictates that the port flip the SBTX and SBRX mappings to SBU1 and SBU2 in order to assure proper sideband transmit-to-receive end-to-end operation.

For USB type-C specification, how is CC1 being opened, and CC2 being terminated considered as flipped plug ?
and why do we need Sideband Use (SBU1 and SBU2) ?

 

Online ataradov

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Re: Questions on USB protocol
« Reply #51 on: November 02, 2021, 04:31:22 am »
I don't understand the question. Device always terminates (pulls down) CC1 and CC2 pins. The cable will only carry one of them to the host and terminate the other one to the ground. This way both sides can determine the orientation of the cable and switch the data lines accordingly.

This is only necessary for SuperSpeed stuff. Legacy LS/FS/HS lines are switched automatically because they are shorted on the PCB. But this means you need two times more pins. For SS they decided to have 4 independent links (2 TX, 2 RX), which requires cable orientation detection and corresponding multiplexing of the TX/RX lines.

SBUx are just low speed channels that are not even necessarily used for data. They may be used to carry audio or some UART stuff. They are just additional pins that are defined by the higher level protocols. By default they don't do anything.

Why do you need all of this? What is your goal?
Alex
 
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Offline Trader

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Re: Questions on USB protocol
« Reply #52 on: November 02, 2021, 04:55:57 am »
 

Offline promach

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Re: Questions on USB protocol
« Reply #53 on: November 02, 2021, 06:04:41 am »
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Device always terminates (pulls down) CC1 and CC2 pins.

It seems to be using pull-up in the case of USB Type-C


Quote
For SS they decided to have 4 independent links (2 TX, 2 RX), which requires cable orientation detection and corresponding multiplexing of the TX/RX lines.

On which exact page of USB specification document does this comes from ?
 

Online ataradov

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Re: Questions on USB protocol
« Reply #54 on: November 02, 2021, 06:18:25 am »
It seems to be using pull-up in the case of USB Type-C
What is using pull-up?

Here is a picture of how CCx pins are used https://microchipdeveloper.com/local--files/usb-i:cable-connection/orientation.png

UFP is the device, DFP is the host. As you can see device pulls down those pins.

On which exact page of USB specification document does this comes from ?
No idea, I have not read the USB3 spec. I just read the summaries and that was enough for my use. It also makes sense from the way USB3 connectors are typically routed.
Alex
 
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Offline promach

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Re: Questions on USB protocol
« Reply #55 on: November 02, 2021, 10:07:09 am »
What is the difference between the two following state diagrams for SINK ?




 

Offline voltsandjolts

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Re: Questions on USB protocol
« Reply #56 on: November 02, 2021, 10:40:51 am »
You should probably ignore the Debug and Test System stuff until you have a functional USB-C device.
And then perhaps continue to ignore it.
 

Offline voltsandjolts

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Re: Questions on USB protocol
« Reply #57 on: November 02, 2021, 10:41:26 am »
@promach

What are you trying to achieve?
 

Offline promach

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Re: Questions on USB protocol
« Reply #58 on: November 02, 2021, 11:50:56 am »
In Figure 4-13, what is DebugAccessory.SNK state for ?
 

Offline promach

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Re: Questions on USB protocol
« Reply #59 on: November 03, 2021, 08:14:32 am »
How do all the following USB PD protocol messages being analyzed/decrypted ?



 

Online ataradov

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Re: Questions on USB protocol
« Reply #60 on: November 03, 2021, 04:50:44 pm »
This is a strange question. They are decoded according to the USB PD specification.
Alex
 

Offline asmi

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Re: Questions on USB protocol
« Reply #61 on: November 03, 2021, 05:23:28 pm »
This is a strange question.
This whole thread is full of strange questions. I'm still at a loss what TS is trying to achieve asking all those questions which can be answered by just reading the spec.

Offline promach

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Re: Questions on USB protocol
« Reply #62 on: November 04, 2021, 06:37:07 am »
USB PD spec alone is not enough, USB Type-C spec is also needed.

See also the actual decoder coding for sigrok


By the way, may I know where I could locate all the USB DevDays presentation slides across the years ?

I only found https://usbpd.wordpress.com/2019/02/07/usb-type-c-pd-presentation-from-usb-developer-days/ and https://www.scribd.com/document/350194505/Usb-Devdays-Hong-Kong-2016-Usb-Pd
« Last Edit: November 04, 2021, 06:59:13 am by promach »
 

Offline voltsandjolts

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Re: Questions on USB protocol
« Reply #63 on: November 06, 2021, 09:54:53 am »
@promach
I see you also post a lot of questions in a similar style (non-interactive, limited feedback, spoon-feeding requests) here, including repeats of some of these usb questions. It's all a bit weird. I'm out.
 


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