[linux-audio-user] Re: Linux Lighting

Dirk Jagdmann doj at cubic.org
Tue Nov 29 12:35:21 EST 2005

> Say I plan lighting for a specific club : is it like each lamp, effect, motor
> will be assigned a to given channel ? I'd then ask the club's technician : "what
> channel is this lamp assigned to ?" (or he'd give me specification)

Yes, for simple lamps it's one channel (thus one byte). However modern 
moving lights and scanners have multiple function and thus use multiple 
channels. Normally each channel controls one function, but for example 
position is sometimes a 16bit value, thus using 2 channels. The big 
disadvantage is, that there is no standard for these modern equipment 
and every manufacturer has it's own function->channel mapping. So you 
have to write a custom "devicedriver" for each moving light type you'd 
like to support. As long as you don't want to spent hundereds of hours 
coding (which will be difficult unless you've got each of those moving 
light for testing available) you have little chance to get anywhere (the 
reason why there's no decent moving light support in any free lighting 
software regardless which OS it runs on.)

However moving lights are generelly better controlled live from a 
dedicated console. So if you are playing in a well equipped club you 
could drive normals lamps with your own software and special effects 
with the local lighting console. Then it's just a matter of merging the 
two DMX streams if the club has all equipment on the same DMX universes.
This merging could either be accomplished with a small external box, an 
DMX input interface for your laptop or perhaps via the lighting console.

> dmx_t buffer[4] = {0x80, 0xFF, 0x80, 0xFF};
> fd = open (DMXdev(&argc, argv), O_WRONLY);
> lseek (fd, 0, SEEK_SET);
> write (fd, &buffer[0], 2 * sizeof (dmx_t));
> lseek (fd, 10 SEEK_SET);
> write (fd, &buffer[2], 2 * sizeof (dmx_t));

This way it would work

> All of this sounds great. But how stable is dmx4linux ? Already used it on real
> live shows ? (I'm not talking about big/huge shows)

Yes we've used it here: (horrible german website)
And others have used it for their events. As far as I can tell there has 
been no report of users having problems due to crashed drivers.

> For a second universe, is it simply a matter of plugging a second Enttec device
> and accessing channels 513-1024 ?

yes. The first interface found is mapped to the first interface. A 
second interface to the second universe etc. If you have two interfaces 
connected when powering on they should be mapped equal with every 
poweron, however that may be buggy. But you can always force a specific 
mapping by hotplugging in the order you'd like.

---> Dirk Jagdmann ^ doj / cubic
----> http://cubic.org/~doj
-----> http://llg.cubic.org

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