This article describes how EDID communication works between a video source device and sink devices.
EDID stands for Extended Display Identification Data. It is a way for a video source to discover the capabilities of the sink (display device) it is connected to. EDID information resides in the sink and is made available through the connection to a source device via HDMI, DP, DVI etc. When a sink is connected to a source it receives power for its EDID circuit from the source.
(This article refers to certain devices as a "sink", which is a generic term for a device that consumes data or information from a "source". In most cases, the "sink" will be a video display like a TV or monitor, but it could also potentially be a video recording device or another device that accepts video signals as inputs.)
The video source will request EDID (extended display identification data) from the sink it is connected to. The sink will then respond with its manufacturer ID and its capability information. This capability information from the sink will define what the display is capable of (preferred resolution, frame rate, other supported frame rates, as well as speaker configuration). The source can now make a choice, to pass its signal if it matches the capabilities of the display, attempt to scale so it matches the display or sends an agreed-upon alternative format or to send something that is not supported.
Initially, EDID was meant to create an easy plug and play solution to connect video sources and sinks from different manufacturers. This can, however, get a little tricky when using multiple sinks receiving video from the same source. What sink does the video source listen to? How does the source handle the differences in EDID between the sinks? Without setting up the system correctly you could have issues when connecting one video source to multiple sinks. Typically this will result in sinks going dark or poor quality images.
EDID in TesiraLUX
With the Tesira LUX OH-1, you can easily manage the EDID conversation with a sink. You can choose to use the format preferred by the EDID negotiation with the sink, or force the OH-1 to ignore the EDID information and output a specific resolution instead.
By choosing a resolution and frame rate from the list the OH-1 will ignore any requests from the sink and only present the format we have selected send to the sink. However, if we choose to use "EDID preferred" the OH-1 will attempt to use the preferred settings that it finds in the sink's EDID data.
If the OH-1 is directly connected to a sink, then there is no chance that the EDID data will conflict with that of another sink. So in a system where each sink is connected to its own OH-1, you can eliminate the possibility of EDID compatibility issues.
Please see the below diagram of this concept. Note the lines that detail where EDID communications are taking place.
When a source is connected to the IDH-1, EDID will flow to the source device from the IDH-1. Inside this EDID traffic, the source will see everything the IDH-1 is capable of. It will then choose how to format and send its signal to the IDH-1. Since Tesira has a scaler on both the input and output with the IDH-1 and the OH-1 there is no need for a specific format to be sent across the network. This means EDID only goes between the source device and the IDH-1.
Troubleshooting possible EDID issues can be isolated to the connection from the input source to the IDH-1 or at the connection from the OH-1 to the sink. This is because TesiraLUX can scale at both the IDH-1 and the OH-1, eliminating the need to send EDID over the network.
EDID problems will often result in no image showing up on the display, or a distorted image showing up on the display. The following steps can help troubleshoot where the EDID problem is happening.
EDID troubleshooting at the IDH-1
- We will first want to make a direct connection between the input source and the IDH-1, taking out any device in between the input source and IDH-1. This will ensure that there are no intermediate devices that are causing the EDID issues.
- Make sure the cables that are being used are in good working order. As a point of reference, HDMI premium cables do not exceed 25 feet in length so you may look at your cables lengths and see if any exceed this. HDMI cables that exceed 25 feet will often still work, however we will want to test with short cables to rule it out as a possible issue.
- We can check that there is a clear path from the IDH-1 across the network by generating a test pattern in the IDH-1 and sending it to an output. If the test pattern displays correctly on the sink then it's likely that something is not working between the input source and the IDH-1. Otherwise, if the test pattern doesn't display correctly, then the problem could be between the OH-1 and the display.
- If you continue to have an issue that you believe are related to EDID you may want to try a different input source to connect to the IDH-1. You may also try connecting the original input source directly to a sink if possible.
- An EDID analyzer can also be used to make sure to check the EDID traffic that comes from the IDH-1. With an analyzer, we should be able to connect it to the IDH-1 and capture the EDID coming from them. This will allow us to make sure that the IDH-1 is correctly sending EDID traffic.
- If you can see the EDID with an analyzer you will want to make sure your input device can send a signal the IDH-1 accepts.
EDID troubleshooting at the OH-1
- We will first want to make a direct connection, taking out any device that may be between the OH-1 and sink. This will ensure that there are no intermediate devices that are causing the EDID issues.
- Next, try sending a test pattern directly from the OH-1 to the sink. You can do this from the AV output block in your Tesira file. Double click on the block and select the output tab and select a pattern that you would like to send. The test pattern will be sent using the output format options also set in the output tab.
- Check what the OH-1 is set to for its output type. You can do this by double clicking on the AV output block for the OH-1 you are working with. From there simply select the output tab and you will see what resolution the OH-1 is outputting. If you have it set to a specific output format you may try changing it to EDID preferred. When EDID preferred is selected and the EDID communication is successful you will see that the OH-1 shows the output format it is using to the right.
- With the OH-1 set to "EDID preferred", if you do not see an output format to the right or the sink is still not displaying your content you may want to check to see that Tesira is receiving EDID traffic from the sink. We can see the received EDID from the connected sink in Tesira's event logs. To access the event logs go to System>Network>Event Log. Then select the system that you want to pull logs from and then press "Retrieve Logs". Within the event log, we can read the EDID captured from the sink device.
- Try connecting the OH-1 to an analyzer to see if the signal passes. For this, you will need an analyzer that can receive an input signal.
- If you are still having an issue try connecting the OH-1 to a different sink. This will help to determine where the issue may lie.
Digital video tools
Other tools helpful when working with video systems are generators and analyzers.
Generators allow you to test and diagnose specific resolution, video timing, EDID and color space issue. Generators will often support a wide variety of display resolutions, frame rates, and chroma subsampling formats which will enable you to test with a wide variety of systems and sinks.
Here are some common feature for generators (not all generators will have the same capabilities):
- Preloaded test patterns
- EDID emulation
- Support/ability to emulate various resolutions
- Support/ability to emulate multiple chroma subsampling rates
- Support/ability to emulate multiple frame rates
- Ability to send audio
Analyzers allow us to read and decipher information from a sink or source device. This allows us to read or see information that is otherwise not viewable to us.
Here are some common feature for Analyzers (not all analyzers will have the same capabilities):
- Analyze input source info-frame and output sink EDID
- Read EDID traffic
- Analyze HDCP compliance of connected devices
- Video timing information
The combination of generators and analyzers can help us to fully test, troubleshoot and understand a video system. Often we see that generators and analyzers come with some of each others functionality and one tool can provide a wide range of abilities. This is a great tool to have when working with digital video systems.
Tesira LUX EDID
List of supported resolutions
Extension Detailed Timing1:2560x1600@60Hz
Short Video Descripter
Audio information within the EDID
EDID hex data
00 FF FF FF FF FF FF 00 09 21 01 00 70 AB 2E 00 0C 1A 01 03 80 00 00 78 0A EE 91 A3 54 4C 99 26 0F 50 54 21 08 00 D1 40 61 40 90 40 A9 40 D1 00 81 80 81 40 81 00 08 E8 00 30 F2 70 5A 80 B0 58 8A 00 00 00 00 00 00 1E AE 29 A0 D0 51 84 22 30 50 98 36 00 00 00 00 00 00 1E 00 00 00 FD 00 0F 3C 0F 87 3C 00 0A 20 20 20 20 20 20 00 00 00 FC 00 42 69 61 6D 70 20 49 44 48 2D 31 0A 20 01 8D 02 03 5A 71 5F 61 60 5F 5E 5D 62 63 64 65 66 67 68 69 6A 6B 4A 4B 4C 52 53 59 5A 01 02 03 04 10 11 12 13 1F 4B 20 21 44 45 48 49 05 06 14 15 22 23 0F 07 07 83 FF 07 00 6E 03 0C 00 10 00 38 3C 2F 00 80 01 02 03 04 67 D8 5D C4 01 78 80 03 E3 05 E7 01 E2 00 EA E3 0F FF 7F 14 69 00 A0 A0 40 2E 60 30 20 36 00 00 00 00 00 00 1E 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 37