Handle a Microcontroller Interrupt | Dataford Interview Questions

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In an Actalent embedded firmware prototype, a microcontroller interrupt status register can report several pending sources at once. Implement an interrupt handler that decodes the status bits and appends one event for each recognized source to a bounded FIFO queue.

Formal Specification

Implement handle_interrupt(status, timestamp, queue, capacity, dropped). status and timestamp are integers. queue is a list of event dictionaries in chronological order, and capacity is its maximum length. dropped is the number of events previously rejected because the queue was full.

Use these status bits:

1: timer interrupt, event type "TIMER"
2: receive interrupt, event type "RX"
4: error interrupt, event type "ERROR"

For every recognized bit, create {"type": event_type, "timestamp": timestamp}. Process events in priority order: ERROR, RX, then TIMER. If the queue is full, do not remove existing events and increment dropped for each rejected event. Ignore unknown bits. Return (queue, dropped).

Constraints

0 <= status < 16
0 <= timestamp <= 2^31 - 1
0 <= len(queue) <= capacity <= 10^5
dropped >= 0
Input queue events are valid and already ordered from oldest to newest

Function Signature

def handle_interrupt(status, timestamp, queue, capacity, dropped):