Northrop M E M O R A N D U M
Precision Products Division

This specification requires knowledge of RCATIER framed Task Queue design and NAHRS embedded flight RTOS

From: Ronald C. Alexander

To: K. H. Lawrence


re: Draft AINS Data Feed Mechanization


     Kinematic data are provided to the Navigation Data
Processor to demonstrate that all subfuntions are accessed
and associated algorithms are executed.  In the absence of a
hardare IMU Interrupt, the System Clock is incremented at
the Loop Rate of a free running Task Queue.  The Instrument
Data is always provided at the System Clock rate.  The
source of Instrument Data is changed on a predetermined
timeline.  New External Data is updated to the MC Data
Buffer and DVA Data Buffer on a predetermined timeline.
Tables of Instrument Data Templates and tables of External
Data Templates are defined for each specific Demonstration

      An embedded Scenario Demonstration Procedure (SDP) is
invoked from background processing after completion of each
Task Queue.  In the absence of a hardware IMU Interrupt, the
IMU Interupt Handler is invoked following Scenario
management.  A change of External Data is emulated only at
Timeline Triggers as defined in an embedded Timeline
Definition Table.  When the System Clock is equal to the
current Timeline Trigger, the SDP will select the next
External Data Template.  The repetition rate for updating
the External Data Buffer from Template is controlled by a
Repetition Code (RC) contained in each External Data
Template.  Regardless of whether External Data is updated,
the SDP will invoke a Scenario IMU Handler (SIH) to update
the Instrument Data.  The SIH will fetch Instrument Data
from the Instrument Data Template selected by the latest
change conditions.  The decision for a change of Instrument
Data Template will occur only at unsolicited change
conditions as they occur based on the External Data and NDP
System Clock.

Data Feed Layout

I SDP Layout

1.   Invoked each pass through the Task Queue from the background.

2.   Inputs:
     1.   System Clock.
     2.   Offset into Timeline Definition Table (TDT).

3.   Outputs:
     1.   Offset into Timeline Definition Table.
     2.   Repetition Code.
     3.   Pointer to current External Data Template.
     4.   External Data Buffer.

4.   Actions:
     1.   Update Timeline Definition Table (TDT) Offset based
          on System Clock.
     2.   Update Point to current External Data Template
          based on TDT Offset.
     3.   Update Repetition Code from Template.
     4.   Update External Data Buffer from Template based on
          Repetition Code.
     5.   Signal Read Tasks based on Repetition Code.
     6.   Invoke SIH.
     7.   Simulate IMU Interrupt.

II SIH Layout

1.   Invoked by SDP.

2.   Inputs:
     1.   System Clock.
     2.   Pointer to current Instrument Data Template from
          External Data.

3.   Outputs:
     1.   Pointer to current Instrument Data Template.
     2.   Instrument Data.

4.   Actions:
     1.   Update Pointer to current Instrument Data Template
          based on External Data.
     2.   Update Instrument Data Buffer from Template.

III Repetition Codes Definition:

1.   Single Shot.
2.   1 Hz.
3.   10 Hz.

IV Timeline Definition Table:

1.   Accessed by:
     1.   SDP.
2.   Variable Length specific to scenario.
3.   Element Structure:
     1.   Element list of Triples of:
     2.   Structure:
          1.   Timeline Key Times for scenario Transitions.
          2.   External Data Template.
          3.   Instrument Data Template.

V External Data Template Table:

1.   Accessed by:
     1.   SDP.
2.   Element Structure:
3.   Variable Length of MC or DVa word records of:
     1.   Variable number of variable Length word records of:
     2.   Structure:
          1.   Variable number of variable number of MC Message Bytes.
               1.   Variable number of Element Lists of:
               2.   Defined by SRS as one of 4 lists of MC data.
          2.   Variable number of DVa Message Bytes.
               1.   Element List of:
               2.   Defined by DVRP Embedded Computer Software Document.
          3.   Repetition Code.

VI Instrument Data Template Table:

1.   Accessed by:
     1.   SIH.
2.   Element Structure:
3.   Variable Length of Instrument Data Template records of:

VII Instrument Data Template:

     1.   Fixed Length word records, TBS Words, of:
     2.   Structure:
          1.   IMU FIFO, TBS Words.
          2.   IMU Distretes Word.

VIII Integration Test Timeline Definition Table:


IX External Data Template Table:


X Instrument Data Template Table:


XI Program Listings: