Bit Error Counters... did they / will they ever exist? - AVS Forum
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post #1 of 12 Old 02-06-2013, 02:49 PM - Thread Starter
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I continue to wonder after reading thread after thread after thread, will "simple" bit error counters that are displayable exist or will they ever be created to be output. With the amount of computing power that now exists in most devices, surely, a simple counter that can be displayed on a device or on screen can't be that hard and would go a long way to help consumers and service centers identify where an issue might be as opposed to "try another cable", "try a different input", "try a different source", etc.... Is there anything in the works in any devices. I like my denon 4308 receiver as it at least displays what type of hdmi video and audio capabilities it has received from the sinks so one can at least figure out whether there is a display capability mismatch.... such a simple status screen. Oh well, just a dream for a better hdmi world. I wonder where the frustration level has to get to before something is done.
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post #2 of 12 Old 02-06-2013, 09:21 PM
 
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It's a good question. The first thing you would need before implementing a counter is a way of detecting the error.

The problem with that is that the current HDMI implementation has no video or audio error correction or error detection bits. In the simplest of schemes, a parity bit is used to determine if an error has occurred. The parity bit basically sums the other bits in the byte and then sets or resets itself accordingly. In order to implement that type of detection, you have to add an extra bit per byte. In the case of error detection and correction more than one byte is needed (usually at least three extra bits).

If you remember back to the beginning of HDMI, the speed of the bit transmissions was pretty much the maximum available in order to send uncompressed video (and audio) along with bits needed for encryption. I believe that an additional parity bit would have made it impossible to implement HDMI at the time. I remember thinking at the time that HDMI was imposed on people too soon, but the content providers demanded it (or something similar) before they would let HD be sent digitally.

Anyway, that's the biggest problem with a counter - no way to detect the errors. If the errors could be detected than it would be possible to prevent things like sparkles or at least make them all black. Unfortunately, the spec just doesn't support it and there is no way to change that without rendering a lot of equipment incompatible.

The second answer is what we often ask our engineers - if you have this information, what are you going to do with it? In our cases, a counter to say bit errors are occurring might help if the cable is bad. Or could it be that the transmitter is bad? Or could there be a firmware error causing the counter to increment? From a manufacturer standpoint, the added complexity for an engineering parameter and the potential for someone who doesn't know what the counter really means could also be a problem.

We used to have something called a "soft error" counter on the Space Shuttle's computers. Sounds bad, right? Actually it indicated the number of times the Shuttle's computers (GPCs) had detected an memory bit error (likely due to radiation) and corrected it. So, as long as the soft error counter kept incrementing once every few hours, it was a good thing. It meant everything was working correctly. But people would get alarmed because some engineer used the word "error" in naming the parameter and people didn't understand what it really meant. There is a danger with any error counter that it could be misinterpretted by those with just enough knowledge to be dangerous.

Now that doesn't mean if I was trying to implement HDMI today and was asked (OK, not very likely) I wouldn't push for some way to either detect errors or (better yet) some way to prevent or correct the errors.

Certainly an interesting question, though.
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post #3 of 12 Old 02-06-2013, 10:47 PM
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Originally Posted by alk3997 View Post

Now that doesn't mean if I was trying to implement HDMI today...I wouldn't push for some way to either detect errors or...some way to prevent or correct the errors.
I would hope you wouldn't even try to implement HDMI, which is nothing more than a monitor connection scheme (DVI) with audio and content protection added, but just a method to allow sending the original compressed signal (all our media is compressed) from the source to the display over a network If someone needs to send an uncompressed signal from a computer to a monitor, they can still use DVI or something similar.
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post #4 of 12 Old 02-06-2013, 10:54 PM
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Originally Posted by budwich View Post

I wonder where the frustration level has to get to before something is done.
Don't hold your breadth. There is no incentive for the CE manufacturers to do anything. HDMI works just fine for most of their customers most of the time. If your total run is less than 25 and you use a single high speed cable, your chance of problems is pretty small. The folks that have problems seem to be the ones that try to push the limits of the technology without paying the necessary price for reliable gear.
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post #5 of 12 Old 02-07-2013, 09:13 AM - Thread Starter
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I think some form of error detection is implemented in the HDMI stream, iirc. what isn't implemented is any error correction, which is fine. In a significant number of home implementations, the signal path isn't a simple source to sink (ie. direct) as originally "planned". As discussed, a simple counter indicating a "pegging" at a avr (input) would indicate an issue on that leg... rapidly changing represent a significant issue, slowly not so much, etc. Similar at a sink. In unison with the receiver, would indicate a problem near the AVR (before) maybe, out of step, not in unison, possibly a further skin on the onion. Off course, the "I should not be getting any errors" comment (demand) will be a possible complaint, but its got to be better than the current "hair pulling" scenarios that are out there now for consumers with little or no information (not even cheap test "sniffers") and I suspect a lot of "NO FAULT FOUND" tickets and returns. I guess, today, every one needs a job even a "call center" type one providing a "try a different input, try another cable" script answer... :-) Oh well, I lament.... the comment that its not that bad for most users is probably accurate otherwise they (manufacturers) would be doing something.
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post #6 of 12 Old 02-07-2013, 09:34 AM
 
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I'm curious - which part of the HDMI stream has error detection? There are some error prevention coding used but that was purely for providing coding that is less susceptible to errors. Other than some keys, I thought everything else did not have any error detection bits?
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post #7 of 12 Old 02-07-2013, 10:55 AM
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Data island packets have ECC. Audio and video have nothing, however because of the 8-10 encoding, if a bit flips, there is something like a 50% chance it will generate an invalid code which is detectable. So, it would be possible to generate some kind of error metric. But, in essence, you already have an analog meter on on the screen: sparkles, messed up lines or parts of lines, complete loss of signal, etc.
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post #8 of 12 Old 02-07-2013, 06:25 PM
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SDI and HDSDI don't have error correction either. They do support error DETECTION but that's all. As the transmission is streamed just like analog and not packet based, you can't request a resend of a damaged packet. There is no time. Now of course you can send packetized video but it's typically compressed. To run realtime HD video or 2K/4K in a packetized format with the ability to resend bad packets before they are needed would take an impractical amount of bandwidth - today.

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post #9 of 12 Old 02-08-2013, 06:23 AM
 
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Quote:
Originally Posted by Colm View Post

Data island packets have ECC. Audio and video have nothing, however because of the 8-10 encoding, if a bit flips, there is something like a 50% chance it will generate an invalid code which is detectable. So, it would be possible to generate some kind of error metric. But, in essence, you already have an analog meter on on the screen: sparkles, messed up lines or parts of lines, complete loss of signal, etc.

Cool - Thanks Colm. I had wondered about that. Yes, and it provides a method for control characters outside of the normal data characters. Really the advantage is to "spread out" any noise so you have less chance of it causing an error, in theory.

It was another IBM idea that didn't become popular until the patent expired. I'd say kind of like microchannel but that never became popular...
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post #10 of 12 Old 02-08-2013, 09:07 AM - Thread Starter
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Good info.... I was thinking further on this.... it doesn't even need to be a display counter. They could make use of all those pretty lights (leds).... :-) TVs have them, receivers too... basically not much different (I think) than providing a "pulse" (blink) related to some "degree" of error rate detected... much like clipping indicators (leds) used on some amps. At least then people will have something to watch instead of "noisy"/flashing/no picture on their TV... :-)
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post #11 of 12 Old 02-08-2013, 12:40 PM
 
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Originally Posted by budwich View Post

Good info.... I was thinking further on this.... it doesn't even need to be a display counter. They could make use of all those pretty lights (leds).... :-) TVs have them, receivers too... basically not much different (I think) than providing a "pulse" (blink) related to some "degree" of error rate detected... much like clipping indicators (leds) used on some amps. At least then people will have something to watch instead of "noisy"/flashing/no picture on their TV... :-)

Are you sure you want to use that method? I can just imagine the quesitons out here -

"My TV's light is blinking. What does it mean?"

"How do I stop the &^#@& light from blinking?"

"The light has been blinking for the last month. Now I'm sure it's blinking faster. How do I stop it from blinking? It's driving my cat crazy. LOL"

"I used to have a red LED blinking on the front of my TV. Now I'm sure the shade of red has changed to more of a pink. How do I get the original red back?"

"My TV is sending me morse code messages through a secret light in the front. It is telling me to write strange questions on the AVSForum. I'm here, what do I do?"

or

"I changed HDMI cables to a more expensive cable. Now the shade of red is purer from the LED and much sharper. Do more expensive cables cause the color to change on the LED?"

I could go on biggrin.gif
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post #12 of 12 Old 02-08-2013, 01:54 PM - Thread Starter
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Actually I like the "morse code" idea... Of course, putting clocks on vcrs that no one was able to set was a great idea... :-) but I think that the current situation of little or no information about the "state" of a hdmi connection will be equally disturbing to a vast number of people, right up there with the clock, flashing blue screen and a few others. Worse, is the industry (technology) is heading more in the direction of complexity without any "aids" to help... but I guess that's the "new job front", service support with a smile and a script.... :-) I personally would like anything that would give some idea of the state of things....AND doesn't cost an arm and leg to implement/deliver.... so if they have a blue led that just "sits" there on my receiver/tv/switch, I would like to see it do something useful. That doesn't mean they can't provide a nice "option" to turn the "display" off if you aren't chasing a comms problem... :-)

I wonder IF some manufacturer actually provided a feature like "displays status of hdmi link to help with any setup / operation issues", how many people would take note... even if they never used the feature other than to see what actually happens..... I guess the cable guys might not be too happy initially... :-(
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