Implement Serial Port Output with UART 16550

UART 16550 serial

COM1 at I/O base 0x3F8 uses a 16550 UART with FIFOs and line status register (LSR). Poll LSR bit 5 (THRE) before writing transmit holding register, or enable receive interrupts via IER. For example, sending 'H' means waiting for THRE then out 0x3F8, al.

Init and transmit

nasmCopy
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• DLAB: Divisor latch access bit in LCR
• IER: Bit 0 enables received-data interrupt
• QEMU redirects COM1 to stdout with -serial stdio
• FIFO reset via FCR improves throughput

QEMU serial wiring

-serial stdio merges COM1 with the terminal so polled output appears instantly. Divisor 1 with 115200 baud is the common lab default when the input clock is 1.8432 MHz. Enable FIFOs via FCR bit 0 to reduce overrun during bursts. Line status bit 0 indicates received data ready for blocking reads without interrupts.

Why for this exercise

You will initialize COM1 and poll (or interrupt-drive) character output. This exercise requires baud divisor setup and LSR polling before each transmitted byte.