CHECKSUM for NULL START CODE? - E1.20 RDM (Remote Device Management) Protocol Forums

-dalc- · May 4th, 2009

Actually SIP packet could be the only way to provide a NULL START CODE packet validation.
Is it possible, in the neare future, to partially modify NSC packet assigning a special use to some slot in order to provide packet validation (eg: slot 1 & 2 = packet lenght, slot N & N+1 = packet checksum) ? It could make DMX more reliable at a price of few slots (eg: 4 slot loss) and mantains full compatibily with the past.

I know that slots are precious for Lighting Designers, but on the other side RDM make possible to free some tipical device control slots like "Device Reset" or "Lamp Control" or some other. (... and I think this should be tell to LDs)

sblair · May 12th, 2009

There are no plans to modify the Null Start code packets. This was proposed many years ago and never really got any traction. There's a couple reasons for this, everything on the link would have to support it to be useful. If a fixture implements it but the controller doesn't, then the fixture would never see "valid" data because there is no checksum.

With the high refresh rate and redundancy of data with DMX512 any corrupted packets are quickly flushed through. If we were going to design DMX512 from scratch today, yes it would most likely be included...but the huge install base doesn't really lend itself to modifying functions of the NSC packet.

If you are having problems with data getting corrupted with NSC packets, then it is likely you have a bigger problem (ie. bad cable) that will be trashing the SIP and RDM packets as well.

ericthegeek · May 13th, 2009

If you need a checksum for Null Start Code (NSC) packets, SIPs are the proper way to do it.

Yes, the checksum *could* be added to the NSC data itself, but either solution will require a firmware update for both the sender and the receiver. Since you have to modify the firmware anyway, doing it with SIPs allows you to have the checksum functionality without breaking the conventions that determine how NSC data is used.

I think SIPs are one of the best features added in the E1.11 revision of DMX. I wish they were more widely used. Sadly, I'm only aware of 3 devices that support SIPs.

-dalc- · May 13th, 2009

OK,
I've just implemented SIP packet handling in my responder.
but now.... I need a conroller that sends SIP!!!
Could you tell me some products that can send SIP?
Thank you very much!

R_Goddard · May 13th, 2009

Goddard Design Co. Lil'DMXter 2 software version 2.40 and up or our DMXter4 RDM both supports Sips.
www.goddarddesign.com
cheer
Bob Goddard

shawn · November 16th, 2018

That's a good idea. I'm going to add them here: TeensyDMX
(Huh, on my browser, that link doesn't show up as a different colour. In any case, it's a link.)

shawn · November 19th, 2018

I just added SIP support (see the two SIP examples) to release 2.5.0 of my TeensyDMX library (https://github.com/ssilverman/TeensyDMX).

May 4th, 2009	#1
-dalc- Junior Member Join Date: Feb 2009 Posts: 7	CHECKSUM for NULL START CODE? Actually SIP packet could be the only way to provide a NULL START CODE packet validation. Is it possible, in the neare future, to partially modify NSC packet assigning a special use to some slot in order to provide packet validation (eg: slot 1 & 2 = packet lenght, slot N & N+1 = packet checksum) ? It could make DMX more reliable at a price of few slots (eg: 4 slot loss) and mantains full compatibily with the past. I know that slots are precious for Lighting Designers, but on the other side RDM make possible to free some tipical device control slots like "Device Reset" or "Lamp Control" or some other. (... and I think this should be tell to LDs)

May 12th, 2009	#2
sblair Administrator Join Date: Feb 2006 Posts: 437	There are no plans to modify the Null Start code packets. This was proposed many years ago and never really got any traction. There's a couple reasons for this, everything on the link would have to support it to be useful. If a fixture implements it but the controller doesn't, then the fixture would never see "valid" data because there is no checksum. With the high refresh rate and redundancy of data with DMX512 any corrupted packets are quickly flushed through. If we were going to design DMX512 from scratch today, yes it would most likely be included...but the huge install base doesn't really lend itself to modifying functions of the NSC packet. If you are having problems with data getting corrupted with NSC packets, then it is likely you have a bigger problem (ie. bad cable) that will be trashing the SIP and RDM packets as well. __________________ Scott M. Blair RDM Protocol Forums Admin

May 13th, 2009	#5
R_Goddard Task Group Member Join Date: Jul 2006 Posts: 10	Goddard Design Co. Lil'DMXter 2 software version 2.40 and up or our DMXter4 RDM both supports Sips. www.goddarddesign.com cheer Bob Goddard __________________ ************************************* Bob Goddard Goddard Design Co. www.goddarddesign.com sales@goddarddesign.com *************************************

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May 13th, 2009	#3
ericthegeek Task Group Member Join Date: Aug 2008 Posts: 378	If you need a checksum for Null Start Code (NSC) packets, SIPs are the proper way to do it. Yes, the checksum could be added to the NSC data itself, but either solution will require a firmware update for both the sender and the receiver. Since you have to modify the firmware anyway, doing it with SIPs allows you to have the checksum functionality without breaking the conventions that determine how NSC data is used. I think SIPs are one of the best features added in the E1.11 revision of DMX. I wish they were more widely used. Sadly, I'm only aware of 3 devices that support SIPs.

November 16th, 2018	#6
shawn Junior Member Join Date: Nov 2018 Location: Oakland, CA, USA Posts: 19	That's a good idea. I'm going to add them here: TeensyDMX (Huh, on my browser, that link doesn't show up as a different colour. In any case, it's a link.)

November 19th, 2018	#7
shawn Junior Member Join Date: Nov 2018 Location: Oakland, CA, USA Posts: 19	I just added SIP support (see the two SIP examples) to release 2.5.0 of my TeensyDMX library (https://github.com/ssilverman/TeensyDMX).