serial - Serial port (UART) driver

Header: kernel/include/kernel/serial.h
Source: kernel/arch/i386/serial.c

Drives the 16550-compatible UARTs for serial I/O. In development builds the serial port is the primary logging channel; all kernel subsystems write progress and error messages via the KLOG family of macros.

Port address constants

Constant	Value	Description
`COM1`	`0x3F8`	First serial port (standard).
`COM2`	`0x2F8`	Second serial port.
`COM3`	`0x3E8`	Third serial port.
`COM4`	`0x2E8`	Fourth serial port.

Logging macros

These macros are defined in the header and conditioned on DEV_BUILD.

Macro	Release build	Dev build
`KLOG(msg)`	no-op	`Serial_WriteString(msg)`
`KLOG_DEC(n)`	no-op	`Serial_WriteDec(n)`
`KLOG_HEX(n)`	no-op	`Serial_WriteHex(n)`

Use KLOG instead of calling serial functions directly so that all debug output is automatically stripped from release builds.

Functions

`init_serial`

void init_serial(int ComPort);

Initialise the UART at the given port address. Configures the divisor for 38 400 baud, 8-N-1 framing, enables the FIFO with a 14-byte threshold, and activates RTS/DSR.

Parameter	Description
`ComPort`	Base I/O address of the port (e.g. `COM1`).

`Serial_ReadChar`

char Serial_ReadChar(void);

Block until a byte is available in the UART receive buffer, then return it.

`Serial_WriteChar`

void Serial_WriteChar(char a);

Block until the UART transmit buffer is empty, then send byte a.

`Serial_WriteString`

void Serial_WriteString(string a);

Send the null-terminated string a over the serial port one byte at a time.

`Serial_WriteDec`

void Serial_WriteDec(uint32_t n);

Format n as a decimal string and send it over the serial port.

`Serial_WriteHex`

void Serial_WriteHex(uint32_t n);

Format n as 0xXXXXXXXX (eight uppercase hex digits) and send it over the serial port.