A kernel's high-water mark for a task reports
Answer: A
The kernel examines how far the sentinel pattern has been overwritten and reports the worst case seen so far, which is exactly what is needed to size a stack with confidence. A figure that never moves after start-up usually means the deep path has not yet been exercised.
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Sizing every task's stack from its measured high-water mark alone is risky because
Answer: B
An error path or an unusual input can add several frames that no test happened to reach, and the measurement says nothing about them. A margin over the measured worst case, plus static analysis of the call graph where it matters, is the safer practice.
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The reason a kernel is usually configured with a fixed number of priorities rather than an unlimited range is that
Answer: C
One ready list per level, and often one bit per level in a lookup word, is what the count buys in RAM. The scheduler itself finds the highest ready level in constant time whether there are eight levels or two hundred and fifty-six.
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A design has 200 tasks on a part with 32 kB of RAM. The immediate concern is
Answer: D
Correct answer: the total stack requirement of the tasks
Each task needs its own stack and its own control block, so 200 tasks consume a substantial part of 32 kB before a single buffer is allocated - a modest 128 bytes each would be 25 kB. The design almost certainly needs fewer tasks, which is the conclusion the arithmetic forces.
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A kernel is described as having a 'zero latency interrupt' capability. This means
Answer: A
Priorities above a configured threshold are left permanently enabled, so their latency is the hardware's alone. The price is that such handlers may not call the kernel, since the kernel's own structures are not protected against them.
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