FPS Sequencer (`milk-seq`)¶

The milk framework provides a powerful standalone sequencer, milk-seq, which runs complex, timing-sensitive command scripts across multiple FPS compute units. By decoupling the sequencer from the milk-fpsCTRL TUI, milk-seq allows for robust, headless script execution and cross-process orchestration via shared memory.

1. Architecture¶

milk-seq operates as an independent backend daemon. It creates a MILKSEQ_STATE structure in /dev/shm/milkseq.<name>.shm and listens for commands on a designated FIFO pipe.

The Component Stack¶

milk-seq Daemon: Headless orchestrator that executes .seq scripts and milk-cli commands.
milk-fpsCTRL TUI: Provides a real-time visual dashboard of the running sequencer. It now acts as a read-only viewer, reading the MILKSEQ_STATE from shared memory.
milk-cli Commands (seq.*): A suite of CLI commands for submitting inputs, checking status, and managing sequencer instances dynamically.

2. CLI Integration¶

You can manage sequencers directly from milk-cli or bash using the seq.* command suite:

Command	Description
`seq.list`	List all running sequencer instances on the system.
`seq.start <name> [-f script.seq]`	Launch a new `milk-seq` daemon headless. Optionally start a script.
`seq.stop <name>`	Safely terminate a sequencer daemon.
`seq.status <name>`	Display the current status, task counts, and errors for a specific sequencer.
`seq.submit <name> <command>`	Push an arbitrary command into a sequencer's FIFO pipe for immediate execution.

Example Workflow:

milk-exec "seq.start calibloop -f calibration.seq"
milk-exec "seq.status calibloop"
milk-exec "seq.submit calibloop load next_step.seq"

3. Scripting Capabilities¶

The sequencer supports a subset of bash-like scripting constructs tailored for high-performance, real-time AO scheduling. These commands are written in .seq files.

3.1 Loop Constructs¶

You can loop blocks of commands using repeat N / endrepeat:

repeat 5
    # Do something 5 times
    sleep 1.0
endrepeat

3.2 Conditional Blocks¶

Evaluate FPS configuration flags before executing commands:

if_fps_status dm_control ON
    echo "DM is running!"
endif

3.3 FPS Synchronization¶

The wait_fps and wait_seq commands pause execution until a condition is met in another process or sequencer, ensuring lock-step synchronization.

# Block until FPS variable changes
wait_fps wfs_camera.frame_ready 1

# Wait for another sequencer to finish
wait_seq other_loop IDLE

3.4 Error Handling¶

You can define an error policy using on_error:

# Options: abort, skip, retry
on_error abort

3.5 Cross-Sequencer Injection¶

Use seq_send to inject a command into another running sequencer's FIFO securely:

seq_send other_loop "load failover.seq"

3.6 Modularity¶

You can compose scripts using the include directive:

# Insert contents of setup.seq inline
include setup.seq

4. The `milk-fpsCTRL` TUI¶

To visually monitor a running sequencer, launch milk-fpsCTRL and press s to toggle the Sequencer panel.

The TUI will automatically locate the sequencer associated with the active module group. If multiple sequencers exist, rely on the unified MILKSEQ_STATE tracking to view real-time process rates, running tasks, and any reported errors.

The TUI handles the sequencer purely as a viewer. Pressing keys to start/stop the sequencer within the TUI will inject commands into the sequencer's native FIFO path, ensuring thread-safe state management.

FPS Sequencer (milk-seq)¶