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Questions on EDID table

Gomathi Chan
Intellectual 535 points


I have a few doubts on EDID table.

1) In Video Data Block in Block 1, short video descriptors (SVD) are mentioned, which includes a native bit. Can only one of the resolutions can have native bit set? From sysfs entry, I came to know that timing for the display we use is 1920x1080. So, only for that resolution I can set native bit in SVD. Am I right?

2) What kind of resolutions require detailed timing descriptors? Why can't we just mention all the supported versions as SVD? Why do we mention few of it (only) in Detailed Timing Descriptors?

  • 0
    TI__Guru**** 161600 points

    Hello,

    Regarding 1) I think your understanding is correct.

    Regarding 2)
     

    Gomathi Chan said:
    What kind of resolutions require detailed timing descriptors? Why can't we just mention all the supported versions as SVD?

    A Vendor Specific Data Block (if any) contains as its first three bytes the vendor's IEEE  24-bit registration number, LSB first. The remainder of the Vendor Specific Data Block is the "data payload", which can be anything the vendor considers worthy of inclusion in this EDID extension block.

    Gomathi Chan said:
    Why do we mention few of it (only) in Detailed Timing Descriptors?

    Same thing, as above, applies for the Detailed Timing Descriptors.

    Some graphics drivers have historically coped poorly with the EDID, using only its standard timing descriptors rather than its Detailed Timing Descriptors (DTDs). It is details that are vendor specific, which are included in the Detailed Timing Descriptors. 

    Hope this helps.

    Best Regards,
    Yordan

  • 0 in reply to Yordan Kovachev
    Intellectual 535 points

    As per the CEA document, I understood that the Video Identification Codes 2 to 5, 17 to 20 and those that have dual aspect ratio requires detailed timing descriptors to be mentioned in the EDID. Is my understanding correct?

  • 0 in reply to Gomathi Chan
    TI__Guru**** 161600 points

    Hi,

    I don't have the CEA document in hand, I'll need some time to acquire it, before I can confirm your understanding. 

    Best Regards,
    Yordan

  • 0 in reply to Yordan Kovachev
    Intellectual 535 points

    Ok, Thanks.  I'm referring to CEA-861-E. 

    But, the following link is for CEA-861-D only. I couldn't find CEA-861-E online.

    http://blogimg.chinaunix.net/blog/upfile2/090903185737.pdf

  • 0 in reply to Gomathi Chan
    TI__Guru**** 161600 points

    Hi,

    IMO, after reading Section 7.2.1 Use of EDID Detailed Timing Descriptors, I think your understanding of video identification codes 2-5 & 17-20  is correct.

    On the other hand Section 7.2.2 Order of Dual-Aspect Ratio Detailed Timing Descriptors states:
    "Monitors that support any dual-aspect ratio timing shall list the preferred aspect ratio before the other and
    shall assume that any signal matching that timing should be displayed at the preferred aspect ratio unless
    receiving an alternate indication in an AVI InfoFrame."

    This means that two timing descriptors are required, one of which is the preferred, hence, I understand, that the use of detailed timing descriptor for dual-aspect ratio timing formats is valid.

    Best Regards,
    Yordan