Embedded Systems

Embedded Systems

1. Applications contain chips that have the power of a whole computer system

   • Charateristics
     • Fewer resources available (memory / storage space)
     • Real-time applications necessary

2. Limited Resources

   • Issues with missing MMU
     • Virtual memory and protection of processes against each other not implemmentable
       • Paging not available
         • copy_to_user and copy_from_user check normally page table - without this cannot check that address of process in main memory (always return true)

3. Real time operating systems

   • Hard real time
     • Completion required within a guaranteed amount of a time
       • E.G. stopping robot within x seconds
       • Cannot not be met by normal time-sharing systems
         • Need dedicated HW
           • E.G. processes that are critical have exclusive access
         • Need adaptions to SW
           • E.G. critical code stays in main memory
   • Time constraints matter - processes need to be executed within a certain time
   • Soft real time
     • Critical process receive priority
       • Pe-emptive priority scheduling and sufficient resources to avoid starvation
       • Short dispatch latency: time between arrival of process and start of execution
       • Problem that context switch occurs after sys-call completion or when I/O takes place
         • Solution: Make kernel pre-emptible
       • Priority inversion
         • Increase priority of process (only done by root)

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