Lab 7 tasks

Work in labs/uart/. Configure the UART, send and receive bytes reliably, and prove the endpoint works before run-pair connects two programs.

Requested functions

• int uart_config(uint16_t base, uint32_t baud, uint8_t line_control)
• int uart_enable_fifo(uint16_t base)
• int uart_enable_rx_interrupt(uint16_t base)
• int uart_set_loopback(uint16_t base, int enabled)
• int uart_send_byte(uint16_t base, uint8_t byte)
• int uart_read_byte(uint16_t base, uint8_t *byte)
• int uart_subscribe(uint8_t irq, lcom_irq_t *out)
• int uart_unsubscribe(lcom_irq_t *irq)

Guided gaps

Validate base port and baud, compute the divisor from the UART base clock, preserve line-control bits around divisor-latch access, add send and read timeouts, and keep loopback setup separate. The divisor-latch bit changes which logical register later accesses use.

IMPORTANT

Always restore line-control state after touching the divisor latch. Otherwise later reads and writes may go to the wrong logical register.

Common mistakes

Missing divisor-latch access before the divisor write, failing to clear it after, sending before transmitter-ready, and treating "no byte" as zero. In a byte stream, these become protocol bugs.

Next: checks and references.