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Flight Software Architecture. Jim Beatty Ohio State. Computing Environment. SBS CR-7 Pentium-III at 700 MHz ‘Stripped’ Linux installation based on RH 9.0 512 MB RAM 256MB configured as RAMdisk. 1 GB Flash disk for system 40 GB solid-state disk for data archive No swap!.

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flight software architecture

Flight Software Architecture

Jim Beatty

Ohio State

computing environment
Computing Environment
  • SBS CR-7 Pentium-III at 700 MHz
  • ‘Stripped’ Linux installation based on RH 9.0
  • 512 MB RAM
    • 256MB configured as RAMdisk.
  • 1 GB Flash disk for system
  • 40 GB solid-state disk for data archive
  • No swap!
issues
Issues
  • The system must never page or swap.
    • Fixed suite of processes
    • Avoid memory leaks
  • Repetitive writing to solid state disk must be limited to well below the device specs.
    • This is subtle, because filesystem data structures are involved and we do not directly control physical writes.
    • Minimize file accesses by appropriate blocking.
  • RAMdisk is our scratch and temporary space and is limited.
  • System must gracefully resume operation on restart.
what goes on solid state disk
What goes on solid-state disk?
  • Events are archived to solid-state disk only after passing the prioritizer.
    • /run/priority/subrun directory tree
  • Command and housekeeping logs are blocked and placed on the solid state disk.
  • Configuration snapshots are periodically archived to the solid-state disk.
    • These include event queue pointer snapshots.
    • We can choose to define a master configuration to be assumed on the next restart.
what goes on ramdisk
What goes on RAMdisk?
  • Packets and file pointers.
  • Current configuration (since modifications via commands may cause multiple writes per change).
  • Log data not yet archived to solid state disk.
  • Logs used for debugging
    • Periodically truncated.
    • Logged to external storage during testing.
how event queueing works
How event queueing works
  • Pointers into the event queues are used to track the next event:
    • for each priority queue
    • for header and for transient packet generation.
  • Checkpoint pointers to archive periodically.
  • On restart, transmission begins from the last checkpoint, but can be commanded to skip to the most recent data.
  • Data ‘in transit’ at the time of reset is permanently lost.
    • Need to understand the impact of this on deadtime determination
  • Playback can be used to fill in gaps