The "Flight Software Architecture" page is based on Tony Waite's diagram of the same name. On this page, it has been turned into an "image map"; some areas are clickable and capable of providing "tooltips" (banners that appear when you hold the mouse over an item). Move your mouse over the diagram; when you're on a sensitized area, the cursor will change its shape.

Prefatory Notes

Any of the FSW "tasks" may, in practice, be performed by a set of VxWorks tasks.

For expository purposes, the diagram splits the GASU into two sections. The upper section details the GASU's output activities (sending data to the EPUs, SIU, and Solid State Recorder). The lower section details the GASU's input activities (receiving data from the EPUs, SIU, and LAT Instrument).

Mainline Data Flow

Event data is sent from the LAT Instrument to the Event Builder portion of the GASU. Once a complete event is available, the GASU sends it to a CPU's LCB (LAT Communication Board), which DMAs it into the CPU's RAM.

When the DMA is complete, an interrupt is generated. The LCB Receive Service fields this interrupt, placing the incoming data in the low-priority input queue of an Instrument Physics slave task. Events that survive the filtering process are turned into CCSDS packets and passed on to the LCB Transmit service, which forwards them (again, via the LCB and the GASU) to the Solid State Recorder.

Ancillary Data Flow

The 1553 (and its associated service tasks) pass CCSDS packets to and from the FSW. Incoming packets tend to be telecommands, forwarded from the Mission Operations Center; outgoing packets tend to be telemetry: reports, repoint requests, etc.