driver.io.serial¶

Serial port (UART 16550) driver.

Overview¶

This unit provides initialisation and byte-level I/O for the four standard PC serial ports (COM1–COM4). It configures the UART for 8N1 operation at a specified baud rate, enables the FIFO, and provides send/receive routines with configurable busy-wait timeouts. A string send helper appends CR+LF, and a hex send helper transmits a 0x-prefixed hexadecimal representation.

Dependencies¶

(none — uses inline assembly for I/O port access)

Constants¶

COM Port Base Addresses¶

Constant	Value	Description
`COM1`	`$3F8`	First serial port
`COM2`	`$2F8`	Second serial port
`COM3`	`$3E8`	Third serial port
`COM4`	`$2E8`	Fourth serial port

Functions and Procedures¶

initPort¶

procedure initPort(port: uint16; baud: uint32);

Initialises the UART at port for the given baud rate: 1. Disables interrupts. 2. Sets the Divisor Latch Access Bit (DLAB) and writes the baud rate divisor (115200 div baud). 3. Configures 8 data bits, no parity, 1 stop bit (8N1). 4. Enables and clears the FIFO with a 14-byte trigger level. 5. Clears the DLAB.

send¶

procedure send(port: uint16; data: uint8; timeout: uint32);

Busy-waits on the Transmit Holding Register Empty bit of the Line Status Register (LSR) for up to timeout iterations, then writes data to the port's data register.

receive¶

function receive(port: uint16; timeout: uint32): uint8;

Busy-waits on the Data Ready bit of the LSR for up to timeout iterations, then reads and returns the byte from the data register. Returns $00 on timeout.

sendString¶

procedure sendString(port: uint16; s: string);

Transmits each character of s followed by CR ($0D) and LF ($0A).

sendHex¶

procedure sendHex(port: uint16; value: uint32);

Transmits the string 0x followed by the 8-digit uppercase hexadecimal representation of value.

soutb / sinb (internal)¶

Inline assembly wrappers for the OUT and IN instructions, each followed by an io_wait call (a zero-write to port $80) to satisfy slow I/O device timing requirements.

Notes¶

No interrupt-driven receive buffering is implemented; all I/O is polled.
io_wait is inserted after every port access to accommodate slow ISA-speed devices.