Sync/kernel/serial.c

/************************
 *** Team Kitty, 2019 ***
 ***       Sync       ***
 ***********************/
 
 /* This file provides an interface to the serial port.
  * Most emulators allow the serial port to be saved into
  * a text buffer, or a file, but this code should work on 
  * hardware with an actual serial port and monitor. */

#include <kernel/utils.h>
#include <stdarg.h>
#include <stdint.h>
#include <stddef.h>

#define SERIAL_DATA_PORT(base)           (base)
#define SERIAL_FIFO_COMMAND_PORT(base)   (base + 2)
#define SERIAL_LINE_COMMAND_PORT(base)   (base + 3)
#define SERIAL_MODEM_COMMAND_PORT(base)  (base + 4)
#define SERIAL_LINE_STATUS_PORT(base)    (base + 5)
#define SERIAL_COM1_BASE                 0x3F8

#define SERIAL_LINE_ENABLE_DLAB          0x80

/**   serial_set_baud_rate:
  *   Sets the speed that data is sent via the serial port.
  *   The default speed is 115200 bits/s.
  *   The argument given is the divisor of the number.
  *   Hence, the new speed becomes (115200/divisor) bits/s.
  *
  *   @param com      The COM port to configure.
  *   @param divisor  The new divisor for the baud rate.
  */

void serial_set_baud_rate(uint16_t com, uint16_t divisor) {
	outb(SERIAL_LINE_COMMAND_PORT(com),
		 SERIAL_LINE_ENABLE_DLAB);
		 
	outb(SERIAL_DATA_PORT(com),
		 (divisor >> 8) & 0x00FF);
	
	outb(SERIAL_DATA_PORT(com),
		 divisor & 0x00FF);
		
}

/**   serial_configure_line:
  *   Sets a specific data byteset in the Serial hardware.
  *   Required for expected operation.
  *
  *   @param com  The COM port to configure.
  */

void serial_configure_line(uint16_t com) {
   /* Bit:        | 7 | 6 | 5 4 3 | 2 | 1 0 |
    * Content:    | d | b | parity| s | dl  |
	* Value:      | 0 | 0 | 0 0 0 | 0 | 1 1 | = 0x03
	*/
	 
	outb(SERIAL_LINE_COMMAND_PORT(com), 0x0B);
}

/**   serial_configure_buffers:
  *   Enables FIFO (First In First Out) on the Serial line.
  *   It clears both the receive and transmit queues.
  *   It uses a 14 byte wide queue.
  *
  *  @param com   The COM port to configure.
  */
  
void serial_configure_buffers(uint16_t com) {
   /* Bit:        | 7 6 | 5  | 4 |  3  |  2  |  1  | 0 |
	* Content:    | 1v1 | bs | r | dma | clt | clr | e |
	* Value:      | 1 1 | 0  | 0 |  0  |  1  |  1  | 1 | = 0xC7
	*/
	
	outb(SERIAL_FIFO_COMMAND_PORT(com), 0xC7);
}

/**   serial_configure_modem
  *   @param com  The COM port to configure.
  */
  
void serial_configure_modem(uint16_t com) {
   /* Bit:        | 7 | 6 | 5  | 4  |  3  |  2  |  1  |  0  |
    * Content:    | r | r | af | lb | ao2 | ao1 | rts | dtr |
	* Value:      | 0 | 0 | 0  | 0  |  0  |  0  |  1  |  1  | = 0x03
	*/
	
	outb(SERIAL_MODEM_COMMAND_PORT(com), 0x3);
}

/**   serial_check_tqueue:
  *   Checks whether the Transmit FIFO Queue is empty on the given port.
  *
  *   @param com  The COM port to check.
  *   @return  0  If the queue is not empty.
  *            1  If the queue is empty.
  */
  
int serial_check_tqueue(uint16_t com) {
	return inb(SERIAL_LINE_STATUS_PORT(com)) & 0x20;
}

/**   serial_write:
  *   Prints a single character to the serial port.
  *   Does nothing fancy.
  *   @param com  The COM port to write to.
  *   @param data The character to write.
  */

void serial_write(uint16_t com, const char chr) {
	//Hang until we have access to the COM port.
	while(serial_check_tqueue(com) == 0);
	outb(com, chr);
}

/**   serial_print:
  *   Prints a string to the serial port.
  *   Does not support ANSI codes, or color.
  *
  *   @param com  The COM port to write to.
  *   @param data The string to write.
  */
 
void serial_print(uint16_t com, const char* data) {
	for(size_t i = 0; i < strlen(data); i++) {
		serial_write(com, data[i]);
	}
}

/**   serial_printf:
  *   A printf-style function for the serial port.
  *   
  *   @param format  The base string - used to substitute the succeding values.
  *   @param ...     The substitutions.
  */
  
void serial_printf(uint16_t com, const char* format, ...) {
	uint32_t storage; //To hold temporary variables
	char stringstore[10] = {0}; //To convert ints to strings.
	va_list list;
	va_start(list, format);
	
	for(size_t i = 0; i < strlen(format); i++) {
		//Check for the format specifier
		if(format[i] == '%') {
			//Check for the other specs
			if(format[i+1] == 'd') {
				
				storage = va_arg(list, int);
				int_to_ascii(storage, stringstore);
				serial_print(com, stringstore);
				empty_string(stringstore);
				i += 2;
				
			} else if(format[i+1] == 'x') {
				
				storage = va_arg(list, int);
				int_to_hex(storage, stringstore);
				serial_print(com, stringstore);
				empty_string(stringstore);
				i += 2;
				
			} else if(format[i+1] == 's') {
				
				serial_print(com, va_arg(list, char*));
				i += 2;
				
			} else {
				serial_print(com, "ERROR: Attempting to parse unknown format string.");
				return;
			}
		} else {
			serial_write(com, format[i]);
			i++;
		}
	}
	va_end(list); //Free the list
}

void init_serial() {
	// Disable interrupts
	outb(SERIAL_COM1_BASE + 1, 0x00);
	
	// Set baud rate divisor.
	serial_set_baud_rate(SERIAL_COM1_BASE, 3);
	// 8 bits, no parity, one stop bit.
	serial_configure_line(SERIAL_COM1_BASE);
	// Enable FIFO and clear buffers.
	serial_configure_buffers(SERIAL_COM1_BASE);
	// Enable IRQs, RTS/DSR set.
	serial_configure_modem(SERIAL_COM1_BASE);
}