Lab 2 Tasks

Work in labs/timer/. This lab is the first one where the code you write is expected to become infrastructure for later labs, so treat naming and state ownership seriously. A later keyboard or graphics exercise should be able to use your timer helpers without copying test-specific code.

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 relying on wall-clock time. Subscribe and unsubscribe should be symmetric: a successful setup should have a clear cleanup path, and cleanup should not depend on unrelated application state.

Once the required functions pass, look at them again as future project code. The tick counter, elapsed-time helpers, and subscription wrappers probably belong in lib/timer/. Lab-output formatting and one-off test harness behavior should stay outside the library.

IMPORTANT

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

Common Mistakes

Typical failures include dividing in the wrong direction, accepting a divisor of zero, writing only one byte of the divisor, and counting ticks in the main loop instead of in the handler. If the tests report a timing mismatch, inspect the computed divisor and byte order before rewriting the whole function.

Next: checks and references.