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Exercises related to Robust Design Patterns - Part 3

MPU Protection

How to handle an exception

Exercice 1

We have seen during the lecture that an exception is raised in case a memory violation occures. Checking the manual contained in the repository:

  1. can you state what function it is? What does its default implementation?
  2. can you infer what thread triggered the violation?
  3. what other pieces of information may one get?

Understanding memory partitioning and zoning

Exercice 2

Look at the following zone to ressource allocation:

  1. Assume the idle task, belonging to Zone_Idle, is run in unpriviledged mode. Is there any issue with the above assignments? Could there be any issue as it can access - at least from the table above - to sensitive areas like ARM_LIB_STACK? (note: ARM_LIB_STACK is reserved for the ARM C library stack)
  2. Take the above ressource allocation and the line of code 
    static uint32_t   sensor_val    __attribute__((section("ram_shared"))) = 0U;
    What does this line do with regard to where sensor_val is put in memory?

Exercice 3

Look at the following code defining threads attributes: 

static uint64_t stack_thrTire[64]; // Stack of Tire Thread
static osThreadId_t tid_thrTire;   // Thread id of Tire Thread

const static osThreadAttr_t attr_thrTire = { // Thread attributes of Tire Thread
.name = "TireThread",
#ifdef SOME_MAGIC
.attr_bits = osThreadUnprivileged | osThreadZone(ZONE_NORMAL_OP) | osSafetyClass(SAFETY_CLASS_NORMAL),
#else
.attr_bits = osThreadUnprivileged,
#endif
.cb_mem = NULL,
.cb_size = 0,
.stack_mem = &stack_thrTire,
.stack_size = sizeof(stack_thrTire),
.priority = 11,
.tz_module = 0,
.reserved = 0};

  1. What does SOME_MAGIC do in your opinion?
  2. Do you see any major differences compared to the way attributes for instantiating tasks have been defined so far?

Safety Class

Activating the functionality

Exercice 4

If you access RTX_Config.h you will see that OS_SAFETY_CLASS exists. Please answer following questions:

  1. is it sufficient to activate OS_SAFETY_CLASS to get the functionality?
  2. if not, what else should one activate?
  3. what is one cannot do when this is activated?
  4. how many files are modified when this flag is activated?

Understanding its way of working

Exercice 5

These are just exemplary questions related to a functionality you are now familiar with: semaphores. The questions related to the code present in the development branch (thus, version > 5.9.1)

  1. what is the check concerning SAFETY_CLASS done when acquiring a semaphore?
  2. what does a call to svcRtxSemaphoreDelete do when destroying a semaphore?