The Attitude and Heading Reference System provides attitude, heading, linear accelerations, and angular rate data to the interfacing system, i.e., the ADIU.  In addition to these parameters, the system shall also provide built-in test information to the ADIU simultaneously.  The system takes external magnetometer data frames and air data frames from the ADIU and uses these data to aid the inertial data.  The system also supports maintenance mode, in which it performs the compass swing procedure for the calibration of the internal and external magnetometers. The system also performs an in-situ firmware upgrade in the maintenance mode, among other functions.  It has both an inertial measurement unit and a navigational unit. Both perform POST and CBIT independently as a part of their health monitoring. Both communicate through a UART interface for the transfer of data using a packet-based data protocol with error checking. A second UART interface is provided for redundancy.

1. AVIONICS CASE STUDY –
IV&V OF ATTITUDE AND HEADING REFERENCE
SYSTEM (AHRS)
Oak Systems Pvt. Ltd.

2. Salient features of the System
v AHRS is a subsystem of Jaguar Darin-III upgrade with focus on
indegenisation with following features
– Provide Attitude (Roll, Pitch) and magnetic heading data to the ADIU.
– Provide body accelerations and body angular rates data to ADIU.
– Provide BIT health status data to the ADIU.
– Accept external magnetometer input data from ADIU as an input to
AHRS.
– Accept True air speed and pressure-altitude data from ADIU for aiding
of AHRS data.
– Use internal algorithm for estimation of output parameters.
– Perform Magnetometer Calibration
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3. Architecture
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4. Major System Functionalites
v Two major independent functional blocks
v Inertial computational Unit (IMU)
v Navigational Unit (NAV)
v Each having its own Built-in tests
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5. About IMU
v IMU handles complex inertial data computations like
acceleration biases using Temperature coefficients,
calibration coefficients with data available from
accelerometers
v Built in tests for checking beyond range accelerometer
and gyro temperatures and also 70 others
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6. About NAV
v NAV provides calibrated Pitch, roll, Yaw data and also
magnetic heading using complex calculations.
v Kalman filter algorithms are applied for all NAV parameters
v Has capability to switchover to internal magnetometers in
case of failure to detect external magnetometer
v About 60 built in tests to provide robustness to system
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7. Trigger for IV&V
As per DO-178B guidelines Independent Verification &
Validation (IV&V) was mandated for DAL (Design
assurance level B with MC/DC)
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8. Scope of Work
To Conduct IV&V as per RTCA - DO178B Level B compliance -
v Planning phase docs review e.g. PSAC, SVP, SDP, SCMP, SQAP, SRS, SDS, SCS
v High level Requirement Verification
v Low level Requirement (Design) Verification
v Code Evaluation (MISRA Standards)
v Requirement based test case preparation (High level and Low level Tests) for 100%
Requirement coverage
v Source Code Coverage (100% MC/DC, 100 % Statement, 100 % Decision)
v High Level and Low level Test Execution (using LDRA tool)
v Traceability analysis:
§ Requirements ó Design ó Code
§ Requirement ó High level Tests
§ Design ó Low level Tests
v Software Configuration Audit
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9. In the Works
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v 450 Functions with cyclomatic complexity ranging from 5 - 55
v Dual language software (C and C++)
v 11000 Executable lines of code
v Complex algorithms viz. Kalman filters, compass swing
v Tight Schedule due to onset of winter for trials
v Distributed Work environment across Multiple cities
v Usage of Multiple testing tools involved RTRT, LDRA to speed up work
v Team size ranging from 3 - 15
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Software Size: 11 KLOC
Language: C, C++

10. Accomplishments
v Provided templates and checklists meeting DO178B guidelines
v Thorough plan document review with emphasis on safety measures needed as a suggestion
v Requirement and design review : Uncovered anomalies in the document in form of
traceability, completeness and correctness w.r.t to DO-178B standards
v Test case creation at both HSI and Unit level with emphasis on uncovering faults to make
system robust by adopting testing techniques like BVA, Equivalence partitioning, arithmetic
precision, fault recovery
v Exhaustive test to handle complex algorithms involved in the project
v Test case execution at both levels with emphasis on 100 percent requirement coverage, 100
percent MC/DC coverage, 100 percent decision coverage and 100 statement coverage
v Clearance from regulators in record time with almost zero turnaround time
v Uncovered 55 Critical and Major defects across HLR and LLR tests
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11. Outcome
Activity/Task Status
Review report of Plan Docs:
PSAC, SDP, SCMP, SRS, SDS, SCS, SQAP, SVP
Delivered
SRD Review report
Delivered
HLR SVCP Preparation
Delivered
SDD Review report
Delivered
LLR SVCP Preparation
Delivered
Code Review report
Delivered
SDD-Code Traceability
Delivered
LLR Test Execution
Delivered
HLR Test Execution
Delivered
IVV Reports (SCI, SECI, SAS)
Delivered
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12. Thank you!
Oak Systems Pvt. Ltd.
#27, NGEF Lane, Off 100 Feet Road,
Indira Nagar, Bengaluru – 560 038, INDIA
Tel : +91-80-4126 7681
Email: contact@oaksys.net
URL: www.oaksys.net
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