utils.c

#include <utils.h>

char nl[] = {'\r', '\n', 0x0};

/* Prints string in buffer on the screen */
void __attribute__((fastcall, naked)) print(const char* buffer){
    __asm__(
            "   pusha                       ;" /* Save all registers */
            "   mov     %cx, %bx            ;"
            "   mov     $0x0e, %ah          ;" /* Video BIOS service: teletype mode */
            "   mov     $0x0, %si           ;"
            "loop:                          ;"
            "   mov     (%bx, %si), %al     ;" /* Read character at bx+si position */
            "   cmp     $0x0, %al           ;" /* Repeat until end of string (0x0) */
            "   je      end                 ;"
            "   int     $0x10               ;" /* Call video BIOS service */
            "   add     $0x1, %si           ;" /* Advace to the next character */
            "   jmp     loop                ;" /* Repeat the procedure */
            "end:                           ;"
            "   popa                        ;" /* Restore all registers */
            "   ret                         ;" /* Return from this function */
           ); 
}

/* For debugging */
void __attribute__((naked, fastcall)) fatal(const char *msg){
    print(msg);
    print(NL);

    __asm__(
            "fatal_halt2:           ;" /* Halt the CPU */
            "   hlt                 ;" /* Make sure itzz */
            "   jmp fatal_halt2     ;" /* Remains halted */
           );
}

/* Clear the screen and set video colors */
void __attribute__((naked, fastcall)) clear(void){
    __asm__(
            "   pusha                   ;" /* Push all registers */
            "   mov     $0x0600, %ax    ;" /* Video BIOS service: Scroll up */
            "   mov     $0x07, %bh      ;" /* Attribute (back/foreground) */
            "   mov     $0x0, %cx       ;" /* Upper-left corner */
            "   mov     $0x184f, %dx    ;" /* Lower-right corner */
            "   int     $0x10           ;" /* Call video BIOS service */
            "   mov     $0x0200, %ax    ;" /* Set cursor position service */
            "   xor     %bh, %bh        ;" /* Page number (0) */
            "   xor     %dl, %dl        ;" /* Column (0) */
            "   xor     %dh, %dh        ;" /* Row (0) */
            "   int     $0x10           ;" /* Call video BIOS service to move cursor */
            "   popa                    ;" /* Pop all registers */
            "   ret                     ;" /* Return from function */
           );
}

void system_halt(){
    __asm__(
            "sys_halt:          ;"
            "   hlt             ;"
            "   jmp sys_halt    ;"
           );
}