Lab 7 Tasks

Work in labs/uart/. The goal is to configure the UART, send and receive bytes reliably, and build enough confidence in the endpoint that run-pair tests can connect two programs together.

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 the base port and baud rate, compute the divisor from the UART base clock, preserve line-control bits around divisor-latch access, add timeouts for send/read waits, and keep loopback setup independent from normal configuration. The divisor-latch access bit is especially important because it changes which logical register later reads and writes refer to.

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

Common mistakes include forgetting divisor-latch access before writing the divisor, forgetting to clear divisor-latch access after configuration, sending without checking transmitter-ready, and treating "no byte" as "received byte 0". These are small mistakes, but in a byte stream they quickly become protocol bugs.

Next: checks and references.