kernel.c

/*
* Copyright (C) 2014  Arjun Sreedharan
* License: GPL version 2 or higher http://www.gnu.org/licenses/gpl.html
*/
#include "keyboard_map.h"

/* there are 25 lines each of 80 columns; each element takes 2 bytes */
#define LINES 25
#define COLUMNS_IN_LINE 80
#define BYTES_FOR_EACH_ELEMENT 2
#define SCREENSIZE BYTES_FOR_EACH_ELEMENT * COLUMNS_IN_LINE * LINES

#define KEYBOARD_DATA_PORT 0x60
#define KEYBOARD_STATUS_PORT 0x64
#define IDT_SIZE 256
#define INTERRUPT_GATE 0x8e
#define KERNEL_CODE_SEGMENT_OFFSET 0x08

#define ENTER_KEY_CODE 0x1C

extern unsigned char keyboard_map[128];
extern void keyboard_handler(void);
extern char read_port(unsigned short port);
extern void write_port(unsigned short port, unsigned char data);
extern void load_idt(unsigned long *idt_ptr);

/* current cursor location */
unsigned int current_loc = 0;
/* video memory begins at address 0xb8000 */
char *vidptr = (char*)0xb8000;

struct IDT_entry {
    unsigned short int offset_lowerbits;
    unsigned short int selector;
    unsigned char zero;
    unsigned char type_attr;
    unsigned short int offset_higherbits;
};

struct IDT_entry IDT[IDT_SIZE];


void idt_init(void)
{
    unsigned long keyboard_address;
    unsigned long idt_address;
    unsigned long idt_ptr[2];

    /* populate IDT entry of keyboard's interrupt */
    keyboard_address = (unsigned long)keyboard_handler;
    IDT[0x21].offset_lowerbits = keyboard_address & 0xffff;
    IDT[0x21].selector = KERNEL_CODE_SEGMENT_OFFSET;
    IDT[0x21].zero = 0;
    IDT[0x21].type_attr = INTERRUPT_GATE;
    IDT[0x21].offset_higherbits = (keyboard_address & 0xffff0000) >> 16;

    /*     Ports
    *	 PIC1	PIC2
    *Command 0x20	0xA0
    *Data	 0x21	0xA1
    */

    /* ICW1 - begin initialization */
    write_port(0x20 , 0x11);
    write_port(0xA0 , 0x11);

    /* ICW2 - remap offset address of IDT */
    /*
    * In x86 protected mode, we have to remap the PICs beyond 0x20 because
    * Intel have designated the first 32 interrupts as "reserved" for cpu exceptions
    */
    write_port(0x21 , 0x20);
    write_port(0xA1 , 0x28);

    /* ICW3 - setup cascading */
    write_port(0x21 , 0x00);
    write_port(0xA1 , 0x00);

    /* ICW4 - environment info */
    write_port(0x21 , 0x01);
    write_port(0xA1 , 0x01);
    /* Initialization finished */

    /* mask interrupts */
    write_port(0x21 , 0xff);
    write_port(0xA1 , 0xff);

    /* fill the IDT descriptor */
    idt_address = (unsigned long)IDT ;
    idt_ptr[0] = (sizeof (struct IDT_entry) * IDT_SIZE) + ((idt_address & 0xffff) << 16);
    idt_ptr[1] = idt_address >> 16 ;

    load_idt(idt_ptr);
}

void kb_init(void)
{
    /* 0xFD is 11111101 - enables only IRQ1 (keyboard)*/
    write_port(0x21 , 0xFD);
}

void kprint(const char *str)
{
    unsigned int i = 0;
    while (str[i] != '\0') {
        vidptr[current_loc++] = str[i++];
        vidptr[current_loc++] = 0x07;
    }
}

void kprint_newline(void)
{
    unsigned int line_size = BYTES_FOR_EACH_ELEMENT * COLUMNS_IN_LINE;
    current_loc = current_loc + (line_size - current_loc % (line_size));
}

void clear_screen(void)
{
    unsigned int i = 0;
    while (i < SCREENSIZE) {
        vidptr[i++] = ' ';
        vidptr[i++] = 0x07;
    }
}

void keyboard_handler_main(void)
{
    unsigned char status;
    char keycode;

    /* write EOI */
    write_port(0x20, 0x20);

    status = read_port(KEYBOARD_STATUS_PORT);
    /* Lowest bit of status will be set if buffer is not empty */
    if (status & 0x01) {
        keycode = read_port(KEYBOARD_DATA_PORT);
        if(keycode < 0)
            return;

        if(keycode == ENTER_KEY_CODE) {
            kprint_newline();
            return;
        }

        vidptr[current_loc++] = keyboard_map[(unsigned char) keycode];
        vidptr[current_loc++] = 0x07;
    }
}

void kmain(void)
{
    const char *str = "my first kernel with keyboard support";
    clear_screen();
    kprint(str);
    kprint_newline();
    kprint_newline();

    idt_init();
    kb_init();

    while(1);
}