@@ -21,3 +21,65 @@ Under this environment, I created a branch in [tasking](https://code.ornl.gov/6o
## Prompt 1
You are working on the tasking project, bl4a-DANGLE-investigation. The code uses the Experimental Physics Industrial Control System (EPICS) as its basis. You had previously performed an investigation of a problem with the S3 motion, and I reference your work in tasking/S3-Gap-Failure-Analysis.md which you should read. The task is to analyze the reason for motion control failure on the DANGLE motor that earlier in the run cycle failed about 3% of the time. There were changes made between 2026-04-06 and 2026-04-08, that now cause scan failures to occur very often. The process variable is BL4A:Mot:DANGLE. You are not executing on the same computer that the system ran on. I have made as much of the environment available to you on this machine, please let me know if there is document that you require. The code that configures the motion is in /home/controls/bl4a/applications/bl4a-Galil1/. The code for the component software modules is in /home/controls/common/*. The log files are in /home/controls/var/log/*. The first failure of its kind occured 2026-04-08 13:36 the requested motion of BL4A:Mot:DANGLE to 8.213476 deg failed. I have made a plot of archive data in /SNS/users/6ov/BL4A/2026/04/09/bl4a-DANGLE-operation-fault-2026-04-08_1335.png; please review it. Since then, repeated failures of scans of BL4A:Mot:DANGLE have occurred. Your task is to do a deep and thorough investigation of the reported files, the documents, the code, the configuration files and try to determine the root cause of the problem. Please be diligent and resourceful. If you need a tool to analyze the data that you do not have, use venv, uv and/or pixi to install it ask me to help you.
```
● The investigation is complete. Here's a summary of what I found:
Findings
Written to: tasking/DANGLE-Motion-Failure-Analysis.md
Root cause (architectural)
profibus.template unconditionally sets URIP=Yes and points RDBL at the Profibus encoder (mDANGLE:EncPos) for every motor with a Profibus encoder — including mDANGLE, a heavy open-loop stepper. The motor record therefore uses the Profibus encoder
(not the Galil step counter) for DRBV. Every Profibus encoder transient is faithfully translated into a relative PR command the stepper physically executes.
The "−6330 step" smoking gun
In the Galil IOC log (/home/controls/var/log/bl4a-Galil1.log), every mDANGLE move since 2026-02-24 shows a characteristic retry pattern: the initial retries converge normally toward target, then a single PRD=-6330±30 steps (= −1.054°) retry
appears, followed by oscillating corrections. The 2026-04-08 13:35 failure is unusual only because two jumps occurred in the same retry sequence, consuming all retries before convergence — the motor ended up ~0.11° below target, just outside the
±0.1° scan tolerance.
Why it got worse between 04-06 and 04-08
Nothing in git changed for any relevant repo, and the IOC was running continuously from 2026-03-26 to 2026-04-09. The change must be operational: air pad / air supply degradation, a bumped detector arm, encoder cable disturbance, or a runtime caput
to RTRY/RDBD (runtime RTRY is observed to be ≥7 while substitutions file default is 5).
Why the 04-09 fix made it worse
Commit 1215877 tightened devices.py DANGLE tolerance from 0.1° → 0.05° on 2026-04-09 after the failure — this turns every single-jump move (most of which used to land between 0.05°–0.1°) into a scan failure.
Key recommendations (full list in the document)
1. Revert devices.py DANGLE tolerance to 0.1° immediately
2. Raise BL4A:Mot:mDANGLE.RTRY to 10
3. Capture runtime values via caput and compare against substitutions defaults
4. Wireshark capture of modbus traffic during a DANGLE move to pinpoint whether the jump originates in the encoder, gateway, or transport
5. Archive raw mDANGLE:Enc at ≥10 Hz to quantify glitch rate
6. Architecturally harden profibus.template with an RDBD sanity check before letting EncPos updates become DRBV
Data I need from the beamline
- /home/controls/var/bl4a-Galil1/bl4a-Galil1.sav* (autosave files — not present on this machine)
- EPICS archiver data for BL4A:Mot:mDANGLE:Enc, .DRBV, .MISS, BL4A:Mot:AirPadStatus covering 2026-04-08 13:35–13:37
- Scan server log from bl4a-dassrv1 for the 04-08 window
- Wireshark capture of 10.111.8.46:502 during a DANGLE move
The screenshots I couldn't fully read (bl4a-DANGLE-persistent-scan-fail.png) were too compressed to extract text — if there are higher-resolution versions or text excerpts from the scan server logs, they'd help confirm how many distinct scan
failures have occurred since 04-08.
```
And the document [DANGLE-Motion-Failure-Analysis.md](DANGLE-Motion-Failure-Analysis.md).
### Prompt 1.1
Ok! I have downloaded the files you requested:
-rw-rw-r-- 1 6ov users 172334 Mar 26 12:51 /home/controls/var/bl4a-Galil1/bl4a-Galil1.sav_260326-125116
I could not obtain 'Wireshark capture of 10.111.8.46:502 during a DANGLE move' because during this time, the wireshark capture system was not running. Regarding the 'bl4a-DANGLE-persistent-scan-fail.png', I hope that 'bl4a-DANGLE-operation-fault-2026-04-08_1335.csv' will suffice as a data export of the values. The bl4a-Galil1.sav* files are all available now at '/home/controls/var/bl4a-Galil1/*' with the two most likely ones being 'bl4a-Galil1.sav_260326-125116' (good?) and 'bl4a-Galil1.sav_260409-120044' (bad?). The EPICS archiver data for 'BL4A:Mot:mDANGLE:Enc, .DRBV, .MISS, BL4A:Mot:AirPadStatus covering 2026-04-08 13:35–13:37' should be in 'bl4a-DANGLE-operation-fault-2026-04-08_1335.csv'. The 'Scan server log from bl4a-dassrv1 for the 04-08 window' should be in '/home/controls/var/scan/console.log'. Thank you for asking! Good luck in your analysis.
