Lab 2 tasks

Work in labs/timer/. This code becomes infrastructure for later labs, so take naming and state ownership seriously.

Requested functions

• int timer_set_frequency(uint8_t timer, uint32_t freq)
• int timer_get_conf(uint8_t timer, uint8_t *status)
• int timer_subscribe(lcom_irq_t *irq)
• int timer_unsubscribe(lcom_irq_t *irq)
• void timer_ih(void)
• uint32_t timer_ticks(void)

Guided gaps

Reject invalid timer numbers and impossible frequencies before writing the control word. Build the control word from named fields, split the 16-bit divisor into low and high bytes, and track ticks without wall-clock time. Subscribe and unsubscribe should be symmetric, with a clear cleanup path that does not depend on unrelated state.

Once the functions pass, review them as project code. The tick counter, elapsed-time helpers, and subscription wrappers probably belong in lib/timer/. Lab formatting and one-off harness behavior stay outside the library.

IMPORTANT

Interrupt handlers should not contain large application logic. Record the event, then let the main loop decide what to do.

Common mistakes

Dividing the wrong way, accepting a zero divisor, writing one divisor byte, and counting ticks in the main loop. If tests report a timing mismatch, inspect the divisor and byte order before rewriting.

Next: checks and references.