Controls

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

i24 runs the Diamond EPICS control stack, the same floor as the other Diamond beamlines. As at I03, 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.

Device handles

CORA models each device's control handle as an opaque string set at the edge. For i24 the EPICS PV prefixes are recorded from dodal (src/dodal/beamlines/i24.py and its device classes), carried confirm because a controls-library snapshot is not a guarantee against the live system (CTRL-1). The PV naming follows the Diamond convention BL<sector><branch>-<DOMAIN>-<TYPE>-<NN>: (for example BL24I-MO-VGON-01: is beamline 24I, motion domain, vertical goniometer 01, and BL24I-MO-CHIP-01: is the fixed-target chip stage). 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), the PSS permit leaves behind the interlocked hutch shutter (PSS-1), and the calibrated values behind the handles.

Timing and triggering

Timing is handled by one FPGA box, a Zebra (BL24I-EA-ZEBRA-01:), modelled as a TimingController device, the same Family the 2-BM Timing device and I22's and I03's FPGA boxes use. The Zebra fans out the TTL triggers and gates: it gates the per-window detector exposure (the Eiger, or the commissioning Jungfrau) and drives the fast sample shutter (BL24I-EA-SHTR-01:, dodal's MXZebraShutter).

What the Zebra hardware-sequences is the serial collection itself. Unlike I03 rotation MX, i24 takes no goniometer sweep: the chip stage (BL24I-MO-CHIP-01:, dodal's PMAC) rasters an addressable chip of thousands of static crystals across the beam, one diffraction snapshot per window, with the detector and fast shutter TTL-gated per window. The detailed trigger graph, the per-window dwell, and the PMAC laser triggers are the serial-collection seam CORA's edge drives, modelled as a Method over the chip stage plus detector rather than as Assets, and deferred pending the team (SSX-1, LASER-1).

The floor: GDA, dodal, and the serial-collection seam

A seam observation, recorded for the eventual Conductor work: i24's acquisition floor is Diamond's GDA, with the device handles above bound from dodal. The serial collection runs as a hardware-sequenced motion program on the PMAC controller: the chip-raster trajectory, the encoder position-compare that fires each window, the laser triggers, and the Zebra TTL gating of the detector and fast shutter. That orchestration is what a future CORA edge replaces, driving through ophyd / EPICS, rather than the EPICS floor itself, which stays the floor.

Two surfaces stay plumbing CORA observes, not data it owns: the OAV zoom and beam-centre configuration, which lives in GDA files (dodal's OAVBeamCentreFile, the on-axis viewer BL24I-DI-OAV-01:, CTRL-1), and the detector file-writing to the Diamond filestore. These are control-system configuration and output, not CORA Assets, recorded because they are what the serial-collection seam reads and writes around.

See Open questions for the control and timing items still to confirm, and Model for the serial-crystallography Capability and the fixed-target chip Fixture carried as deferred CORA decisions.