DMX Plugin Question

[RJ]

KC,

In the plugin for the ENTEC OPEN DMX does the api give you the ability to do short frames? I notice that no matter how many channels I am using on my dimmer vixen sends all 512. I know this is considered normal for dmx but most setups allow you to do partials and this increases the frame rates. I was looking to be be able to handle 25ms event timing on my personal LYNX dimmers but with the cheap open dmx unit It's just a little too slow to handle it. On a side note I guess with 512 channels thats not bad speed but being able to limit it to say 256 channels could double the refresh rate and this would get me under 25ms. Just a though to think about when your sitting around nothing to do wishing you had something to work on. :lol:

[DynamoBen]

The refresh rate has nothing to do with the number of channels. The USB interface can't handle anything faster without data integrity being sacrificed. As far as fewer channels, in the end you would just have fewer channels at the same speed.

[RJ]

I would still like to know if you can do it or not KC.

Ben not sure if you misunderstood me but I am not speaking of data rates. I am speaking of number of frames. Since DMX frames are all at a set data rate and since this requires them to take 44us each and not taking in to consideration the time it takes for the start break 256 channels would require 44us * 256 not 44us * 512. This allows you to start agian with the next seqence of frames twice as fast. This is not changing the data rate or requiring the usb to operate any faster. This is allowed in DMX you are not required to send all 512 frames. most DMX console do this and I am asking if the unit will allow KC to send the number of channels we are using instead of all 512 always. As far as data rates go the DMX standard is locked at 250k and with this the standard if met to the letter would provide 44hz refresh rate which would be a 22.72 ms event timing at 512 channels. So not sure where your usb limit comes in. The Chipset they are using I assume is limiting it but I can do 10 mbs on usb without breaking a sweat so the usb port is far faster than the dmx can handle. In reality most consoles only make 35 - 40 hz refresh so that is around 30 ms event timing. I do not expect these cheap usb dmx units to match that but at 256 channels we could still easily handle 25ms events in vixen. This is good enough how many people are running more than 256 channels? If so they can run more at 50ms. If not I will settle for the 50ms on 512 channels I'm getting now and be happy but I always have to push the limit for it to be better. :twisted:

P.S KC the full 256 levels on the new dimmer is awesome. Thanks

[DynamoBen]

...you are not required to send all 512 frames. Most DMX console do this and I am asking if the unit will allow KC to send the number of channels we are using instead of all 512 always.

OK I have to disagree here. Most consoles do not do this! I have been in the professional lighting industry (both concert and theatrical) for almost 2 decades. I also worked for a major theatrical dimming and controls manufacturer for a portion of this time. Only inexpensive bottom of the line consoles transmit truncated dmx streams (below 512). Yes the standard allows this sort of truncation but its a bad practice.


As far as data rates go the DMX standard is locked at 250k and with this the standard if met to the letter would provide 44hz refresh rate which would be a 22.72 ms event timing at 512 channels. So not sure where your usb limit comes in. The Chipset they are using I assume is limiting it but I can do 10 mbs on usb without breaking a sweat so the usb port is far faster than the dmx can handle.

The limit has to do with the FTDI driver and chipset. That being said the speed its running is plenty fast for any dmx application.


In reality most consoles only make 35 - 40 hz refresh so that is around 30 ms event timing. I do not expect these cheap usb dmx units to match that but at 256 channels we could still easily handle 25ms events in vixen. This is good enough how many people are running more than 256 channels? If so they can run more at 50ms. If not I will settle for the 50ms on 512 channels I'm getting now and be happy but I always have to push the limit for it to be better.

I guess in the end I'm not sure where the requirement for a high refresh rate is coming from. According to the DMX spec devices need to function at very low refresh rates. We aren't even close to "very low" with this DMX converter. In the end if you are looking for a faster refresh rate you may want to invest in the DMX Pro. Hopefully KC will be able to release the plug-in for the Pro in the next few months. That will give you the high refresh you are requesting.

In short making this change to the current plug-in can cause a number of different problems. So its not an option at this point. :(

[RJ]

OK I have to disagree here. Most consoles do not do this! I have been in the professional lighting industry (both concert and theatrical) for almost 2 decades. I also worked for a major theatrical dimming and controls manufacturer for a portion of this time. Only inexpensive bottom of the line consoles transmit truncated dmx streams (below 512). Yes the standard allows this sort of truncation but its a bad practice.

Sorry the four I checked the specs on all did it I guess they were all cheap ones. (not to be read as sarcastic I really mean I might have looked at all cheaper. but they did it so it looked to me as most did it.)


The limit has to do with the FTDI driver and chipset. That being said the speed its running is plenty fast for any dmx application.

Glad you agree with my statement about usb

I guess in the end I'm not sure where the requirement for a high refresh rate is coming from. According to the DMX spec devices need to function at very low refresh rates. We aren't even close to "very low" with this DMX converter. In the end if you are looking for a faster refresh rate you may want to invest in the DMX Pro. Hopefully KC will be able to release the plug-in for the Pro in the next few months. That will give you the high refresh you are requesting.

The requirement is mine I would like my dimmers to work on the cheap dmx dongle at 25 ms event timing.

In short making this change to the current plug-in can cause a number of different problems. So its not an option at this point. :([/quote]

Sorry didn't understand that it was you who decided what KC does and does not do with his software. I'll take note of it.


To sum up this up so far:

I ask KC if he has the ability to do something.

you told me I didn't know what I wanted and it would not refresh rate.

I said I would still like to know and explained what I understood as a misunderstanding on your part of what I was wanting to do.

You explained you were a DMX expert (which I already knew from many other post.) That it is done sometimes, That I didn't need it, That you didn't like the idea and that it wasn't going to happen.

This is the way I see it.

So I ask again KC (not Ben) can you control in the open dmx driver the number of channels sent and if so could you give us the option in the current or a different plugin to have it output the number of channels vixen is controlling. Preferable in a copy of the plugin named something else so this bad idea will not effect anyone who does not want it? I don't feel this will impact anyone else so see no reason for objections to it from others.

If I use it and it blows up my house than it will be my problem. I will release you of all blame in ruining my life, making me bald, turning my friends against me or any other horrible thing that would arising from me upsetting the DMX gods KC
thanks :lol: RJ

Remember it's Blinky Blinky it's not this serious. :D

[fkostyun]

** post deleted by author

[wjohn]

i had nothing of value to add to the topic, but i thought that i would add a post, just so people know that I, too, am cleva.

John.

[DynamoBen]

First off I keep all my posts technical and non-personal, I'm not trying to tell you what you need. I was trying to provide some insight into the plug-in and its hardware. My post(s) were intended to describe what the plug-in can and can’t do, and why. I was also inquiring about the need for the change, and then offering a possible solution.

I had a big part in the plug-ins creation and I know first hand how difficult it was to implement and test it. Even small alterations to the code made it unusable (KC can vouch for that) which is why I said it wasn’t an option at this point. Making this change goes further than just having KC update the code; I need to verify it because KC doesn’t have the hardware and DMX testing tools that I have. So for this plug-in it’s a cooperative effort between him and me.

In the end you are right, I'm not KC and I can’t speak for him. I’m sorry I even posted, and I apologized if I offended you.

[RJ]

I am sorry to have engaged my fly of the handle mode. It is one(of many) of my faults. I was cool with everything you had said till the "So its not an option at this point" I'm afraid the way I read that was "I have deceided that will not be made avaliable to you" This pushed one of the buttons that some of us have. Up till then I really was just explaining in details what I was up to. I had an email from someone that I know fairly well on the board to tell me he felt a couple of things were smart #$$ of me to say in the second post and this tells me I came across wrong. The only thing that was wrote to be that way was the last post. and even alot of it was not inteneded that way. one he pointed out was my comment about you being an expert in dmx. I truely meant that I have read enough of your post to know you are very knowledged in it. You are correct in that I will buy a pro when vixen has a plugin for it but I was really looking to get more out of the cheap unit for others. I thought it would help one of your and I causes along (convincing people to go DMX on these system) If they could buy an inexpensive unit and get the rates they are going to want with channel counts that they will really have. It very well may not even be possible to do with the drivers provided. But if so it most likely would be a parameter passed to the dll which would be easy enough to do. It really was not worth me loosing my cool over and giving even more people a reason to dislike me on the forum. Your last post simply shows the class act that you are. As far as offending me this is the lest you should be concerned of and I hope you can brush off my ill comments. I should have walked away from the computer for a few minutes and wouldn't have typed them. I do this for the enjoyment and so far that has come from seeing people build things I had a hand in and using them. Every time I see a new Grinch or Ledtriks complete I smile a little more. So far this has been it for me I have never even had a show of my own.

[KC]

After a discussion like that, in the very least, I can look into it.

I am able to send fewer bytes, that part is definitely doable. The Write() function isn't too picky, just a generic device write.

But I am concerned about what a change would do. In looking at the code, I remember Ben and I spending a long night trying to get the timing just right so the output stream was stable, according to the device. A millisecond either way in the timing and the stream became unreliable. I think that's what Ben was talking about with small alterations.

So, technically, yes, it can be done. But the varying frame length may cause timing problems, giving you a flaky response from your device.

[P. Short]

More out of curiosity than anything else, what does that mean? It is surprising to me that there was any timing sensitivity at all, unless the Entecc controller is lacking in memory.

--

Phil

[DynamoBen]

The Enttec device doesn't have any memory. For that dongle to work all the DMX packet information and timing needs is handled by the host PC. The Open DMX device is just a FTDI USB-to-Serial adapter connected to a RS485 transceiver (75176). Altering the plug-ins timing did cause issues, hence my hesitation for changing it. It’s the whole "leave well enough alone" thing.

The DMX Pro on the other hand generates DMX from the onboard microcontroller. All the host PC has to do is send channel intensity updates as they happen.

[P. Short]

Leaving well enough alone sounds like a good idea to me in that case. Not that anyone asked me.

--

Phil

[RJ]

Then I agree I believe we need to look at recommening the pro or something else. Unless ( and this is a possible I guess ) that I'm having my own issue with running it on this computer (3.2 gh) its just not as quick as I had hoped. Hence the request. I dont mind spending the extra as I am going all dmx but I wish we could offer a good cheap alternative to the rest of the DIY'ers. On the other side of it would you guys be willing to let me hack on a copy of the plugin as I can test the dmx and if I was able to do it and if it did what I am hoping we could use this cheap unit for the masses and have refresh rates they will be happy with on less than 512 channels and I dont think I can hurt my copy of vixen with a bad copy of a plug in. If I make it work I will send KC and Ben the modified version to test and distribute if they feel its ok. If I can't nothing but a little lost time on my side.

[DynamoBen]

So the question that I still have is where does the need for a higher fresh rate come from? Are you seeing steppy dimming?

[RJ]

No, I am putting the dimmer though the toughest testing I can and seeings what kind of event timing it will handle. The toughest test I could come up on that was to setup vixen with a given event timing and and blink a channel at that. at 100ms perfect, at 50ms, best I can tell perfect, get much lower, missed events. of course it syncs back because vixen is still kicking out the right info at the write time. From what I can tell the full dmx string out of the dongle is taking just a little longer than that to complete so over say 10 cycles of the lite it reaches a point where the dmx string is behind and starts the last command just before vixen gives it the next levels. This makes it miss that packet. by the time dmx sends the next string with the update we are ready for the next state of the light and you have a partial event that looks as if we missed an event. Then all is good for maybe 9 more dmx passes. I know this is a muddy explaination but I hope you understand. the DMX refresh is just a little to slow for this kind of event timmings. I also see sometimes the dmx stream is not like clock work. I believe this is the nature of the beast with the open as it has no brains and if the computer gets an interrupt or is busy at the wrong time this could lead to this. I keep all but the needed processes going on the machine to help and I dont know that its noticable in the lights as a whole. But maybe this is part of the problem on the low event timings also. Most people will not need 25ms but everytime a controller has been design on here before it was asked for by some. KC I think the old joke was they wanted to Twinkle the lights. and the answer was (what ever that is). Funny thing is other than the money difference the Pro unit woud be better, and the plugin would be bone simple to write for looks like you simple use the virtial com and stream the values to it. But on a side note I have an idea that I am posting in the DMX section cause it belongs there as its hardware. Will both of you read and give me feedback on it? Thanks

[DynamoBen]

Well it sounds to me like a two part issue, its sounds like the level changes aren't making into/out of the plug-in fast enough and this may be due to DMX's refresh rate; some level changes are being skipped/dropped.

Values being skipped/dropped isn't really a surprise. During a fast fade several values may be skipped/dropped, even with skipped values when dimming or controlling moving lights visually you wouldn't notice. There is a small chance you may notice with LEDs, and you would defiantly see it on a DMX tester. In the end DMX isn't really designed to transmit every single level change, the limitation as you suggested is the refresh rate of the packet and the inter-byte spacing. Top of the line consoles have a direct "pipe" to the DMX interface and start a new packet immediately after the previous one. They also don't have any inter-byte spacing. If memory serves KC had to add inter-byte spacing to ensure data integrity to the Open DMX dongle, hence the slower refresh rate.

[RJ]

That would explian why the refresh rate is not as fast as I would expect. I do not notice anything in the fade its flashing the lights where I see it.