Controls

The control stack and trigger scheme. Design-phase, with the dodal-derived handles recorded.

I22 runs the Diamond EPICS control stack. The crucial difference from the other design-phase scaffolds is that the control handles are known: Diamond's open dodal library records the real EPICS PV prefix for each device, so this scaffold carries pv on every device rather than leaving it empty.

Device handles

CORA models each device's control handle as an opaque string set at the edge. For I22 the EPICS PV prefixes are recorded from dodal (src/dodal/beamlines/i22.py and its device classes), carried confirm because a controls-library snapshot is not a guarantee against the live system. The PV naming follows the Diamond convention BL<sector><branch>-<DOMAIN>-<TYPE>-<NN>: (for example BL22I-MO-DCM-01: is beamline 22I, motion domain, double-crystal monochromator 01); the undulator and machine devices use the SR22I storage-ring root. The full handle list is in the Inventory.

What dodal does not give, and so is not invented: which access-gated hutch each device sits in (the PV encodes a functional zone, not a hutch or its PSS meaning, ENC-1), and the calibrated values behind the handles (limits, energy range, beam-center, camera lengths).

Timing and triggering

Timing is handled by PandABox FPGA hardware, the same family Diamond uses across its bluesky beamlines:

• Two PandABox units (BL22I-EA-PANDA-01:, BL22I-EA-PANDA-02:) generate the triggers and gates and capture to HDF. dodal carries two more (Panda3 / Panda4) that are skip-flagged, so they are not modelled.

The scheme is modelled as TimingController devices, the same Family the 2-BM Timing device (the softGlueZynq box) uses, confirming that "timing-generation is a first-class device" generalizes from the APS pilot to a Diamond beamline. How the PandABoxes bind to the detectors and flux monitors (trigger fan-out, the master clock) is a Method concern carried as TRIG-1.

The floor: GDA and bluesky

A seam observation, recorded for the eventual Conductor work: I22's acquisition floor is Diamond's GDA (Generic Data Acquisition) plus the bluesky/blueapi layer that dodal feeds, listed in the descriptor's software_iocs_not_modeled. These are control-system software, not CORA Assets. They are recorded because they are what a future CORA Conductor would orchestrate over or replace, the Diamond analogue of the APS tomoScan seam: I22 tests whether "replace the technique orchestrator" reads the same against a GDA/bluesky floor as against the APS EPICS-scan floor.

See Open questions for the control items still to confirm.