AUTSat MicroSatellite Software and Operating System Morteza Ansarinia Mostafa Salarirad 

• Separated functionality into multiple physically independent hardware subsystems • Single integrated hardware. Softwares control subsystems 

• Multitasking • Resource allocation • Reliability, safety and software recovery 

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Application Layer Operating System Hardware Abstract Layer Hardware 

Processor Reset Initialize Hardware Initialize C/C++ Runtime. Jump to main() Initialize and Start Kernel Create Default Threads (Supervisor, ...) Power Thread Thermal Thread Health Checker Thread ACDS Thread Payload Thread Supervisor Thread Telecommand Thread Telemetry Thread Hardware Abstract Layer 

Operating System MicroC/OS-II Pros ANSI C Preemptive Multitasking Semaphore, Mutex, Timer, Message Management Fixed Sized Memory Management Low Cost (Free), Low Size Reliable, Low Interrupt Latency 

Operating System MicroC/OS-II Cons No Object Oriented Support Complicated Message and IO Management No Error Recovery Fixed Sized Memory Management ... 

Operating System Improvements • Object Oriented Kernel • Integrate Interrupts, IO, Message, ... into “Message” • Hardware Abstract Layer • Filesystem • Exception Handling • Error Recovery • Bootloader • ... 

Operating System AnytimeOS Kernel namespace OS { } Thread Timer Queue Event Message Mutex List Priority Queue Semaphore Scheduler Port 

Operating System Filesystem • saveBool ( “power.health” , true ) ; • saveInt ( “thermal.sensors.count” , 50 ) ; • saveDouble ( “power.temp” , 24.2 ) ; • saveString ( “error.module.name” , “c&dh” ) ; • bool health = getBool ( “c&dh.health” , true ) ; 

Operating System Thread Structure • Main() • init() • halt() • Thread Workspace • newInt() • newDouble() • newBool() 

Operating System Scheduler • Unlimited number of threads • Round Robin Thread Scheduling • Same Priority • Avoid Priority Inversion • Dynamic Priority 

Operating System Mars Pathfinder (1997) • A few days into the mission, the spacecraft began experiencing system resets. • Official Report: • software glitches • the computer was trying to do too many things at once 

Operating System Mars Pathfinder (1997) ... The failure was identified by the spacecraft as a failure of the bc_dist task to complete its execution before the bc_sched task started. The reaction to this by the spacecraft was to reset the computer. This reset reinitializes all of the hardware and software. It also terminates the execution of the current ground commanded activities. No science or engineering data is lost that has already been collected (the data in RAM is recovered so long as power is not lost). However, the remainder of the activities for that day were not accomplished until the next day. The failure turned out to be a case of priority inversion. ... Glenn E Reeves Software Team Leader 

Operating System Priority Inversion a low priority task holds a shared resource that is required by a high priority task 

Operating System Priority Inversion Solutions 1. Disable all interrupts to protect critical section • Keep critical sections very brief, under 100uS in practical systems • Core::lock() • Core::unlock() 

Operating System Priority Inversion Solutions 2. Priority Ceiling 

Operating System Priority Inversion Solutions 3. Priority Inheritance • Keep medium priority threads from preempting the low priority thread • Scheduler::doSchedule() • Thread::waitOnSemaphore() • Thread::waitOnMutex() 

Operating System Self Healing and Recovery 1. Exception Handling 2. Component Micro Rebooting 3. Watchdog-Based Recovery 

Operating System Self Healing and Recovery 1. Exception Handling - Commonly used to signal error conditions in application codes. - Allows system developers to write code to handle errors like illegal opcodes in the OS using C++ “catch”. 

Operating System Self Healing and Recovery 1. Software Watchdog Recover Livelocks (can’t prevent infinite loops) 

Operating System Self Healing and Recovery 2. Component Micro-Rebooting - Most of OS components supports init(), reset() and stop() 

Simple Application 

Simple Application simple.hpp #include using namespace OS; Workspace workspace (1024); Class SimpleThread : Thread { public: SimpleThread() : Thread(“SimpleThread”, 100, workspace); protected: virtual void Main(); } SimpleThread simpleThread1(); SimpleThread simpleThread2(); SimpleThread simpleThread3(); 

Simple Application simple.cpp #include virtual void SimpleThread::Main(){ printf(“Hello World!”); } 

Operating System Bootloader - Two Operating System (Simple, Normal) - Download OS image from the ground station