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RDM Interpretation Questions Discussion and questions relating to interpreting and understanding the E1.20 RDM Standard. |
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May 1st, 2012 | #1 |
Junior Member
Join Date: Apr 2012
Posts: 7
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PID vs. PDL
Hey all,
while writing the Wireshark dissector I ran into a RDM packet that I don't know how to handle. It has a PID of 0x0401 (LAMP_HOURS) and a PDL of 2. But the spec (just bought the new one to verify) says that LAMP_HOURS should be a 32bit value. So, or the PID is wrong, or the PDL is wrong. How should one deal with situations where PID and PDL disagree ? - Erwin |
May 1st, 2012 | #2 |
Junior Member
Join Date: Apr 2012
Posts: 7
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Hmm the image was resize to unreadable size, but it just shows how Wireshark dissected the wrong packet.
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May 1st, 2012 | #3 |
Task Group Member
Join Date: Jun 2006
Posts: 181
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Erwin
not sure which version you have, but in ANSI E1.20 - 2010 Entertainment Technology RDM Remote Device Management Over DMX512 Networks Copyright 2011 PLASA NA. All rights reserved. CP/2009-1017r2 Approved as an American National Standard by the ANSI Board of Standards Review on 4 January 2011. section 10.8.2 Lamp Hours PID is described with a PDL of 0x04 as you would expect. It is also correct in a final draft which I, as a task group member, have. What page are you referring to ? Peter Willis |
May 1st, 2012 | #4 |
Junior Member
Join Date: Apr 2012
Posts: 7
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Hey Peter,
Yes the spec says LAMP_HOURS is 32bit, and that's the way I implemented it in Wireshark. But I have a capture file from someone that has a LAMP_HOURS PID with a PDL of 2. The question should probably more be like; when PID and PDL disagree, should I assume spec is always right and mark the packet as broken? |
May 1st, 2012 | #5 |
Task Group Member
Join Date: Jun 2006
Posts: 181
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In essence YES - even if the spec is "broken". It is the spec, warts and all, and is the only common reference we have!
In the example you cite, the capture file is evidence of a non-compliant device. Peter |
May 1st, 2012 | #6 | |
Task Group Member
Join Date: Aug 2008
Posts: 375
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Quote:
This is a common problem, I've seen many devices that send incorrect PDLs, especially on ACK SET_RESPONSE packets. Such behavior can cause interoperability problems. |
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