3 Replies Latest reply on Jan 15, 2020 4:58 PM by HirotakaT_91

    About  ALT mode log for SVIDs




      Before evaluating the CCG3PA, a customer asked us to deepen their understanding of ALT Mode.

      Attach log when HDMI adapter is connected to macbook.

      Line 32 responds to the Discover Identity command with Modal Operations set to 1.
      Q1) This is the recognition that this line describes the exchange of both HDMI adapter and Macbook. Is it correct?
      Q2) Also, if Modal Operation is Yes, I understand that the target device supports DP. What is the general case where Modal Operation is Yes and No.

      The supported SVID is returned in response to the Discover SVID command on line 34.
      Q3) In the log, SVID 0 returns 0xFF01 (DisplayPort) and SVID 1 returns 0x5AC. Why did it return two SVID codes? Is it ok there are SVIDs? Because In the PD3.0 standard document (Table 6-25 Structured VDM Header),  B0 to B15 have meanings other than SVID.

      Q4) In response to Discover Modes on line 38, there is a response to Discover Modes on line 40. But which part is true response/explanation  for Discover Modes?


      Best Regards


        • 1. Re: About  ALT mode log for SVIDs

          A1 A2) Modal Operation states where there are one or more Active Modes.  Modal Operation ends when there are no longer any Active Modes. It shall be set to one if the product supports Modal Operation. It shall be set to zero otherwise.


          A3) "Discover SVID Responder VDO" is not VDM Header. Please read the chapter of "  Discover SVIDs" in the PD Spec.


          A4) Discover Mode of Discover Modes Responder ACK contains Mode information.

          I am not clear what the question is. Please go through the chapter of "  Discover Modes" in the PD Spec.


          Best regards,

          Hirotaka Takayama

          • 2. Re: About  ALT mode log for SVIDs

            Hello Takayama san


            Line 36 responds to the Discover Identity command, and there are two SVIDs below.

            SVID0: FF01:   Discover Modes for Display Port

            SVID1: 0x5AC: Discover Modes for Apple SVID

            So, I am understanding that the SVID field Shall contain either a 16-bit USB Standard ID value (SID) or the 16-bit assigned to the vendor by the USB-IF (VID). No other value Shall be present in this field.


            Q) I want to know the reason why there are two SVIDs mentioned above for Line 36


            Best Regards


            • 3. Re: About  ALT mode log for SVIDs

              The client board reports an SVID of 0xFF01, which is an ID assigned to a DisplayPort connection.

              0x05AC is VID for Apple and we do not know the detailed apple specific alt mode standard. Ask Apple if required.