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/* Handles the keyboard interrupt */
void keyboard_handler(struct regs *r)
{
    unsigned char scancode;

    /* Read from the keyboard's data buffer */
    scancode = inportb(0x60);

    if (scancode & 0x80)
    {
 
        if (scancode==42) { shift=0; }  // check values of shift, ctrl and alt
        if (scancode==54) { shift=0; }
        if (scancode==29) { ctrl=0; }
        if (scancode==56) { alt=0; }

    }
    else
    {
        /* Here, a key was just pressed. */

        if (scancode==42) { shift=1; }  // check values of shift, ctrl and alt
        if (scancode==54) { shift=1; }
        if (scancode==29) { ctrl=1; }
        if (scancode==56) { alt=1; }
        if (alt!=1) {                  // keypresses do not count if alt or ctrl are
            if (ctrl!=1) {            // being held down during the keypress.
                 if (shift==1) {                   
                       if (showkeypresses==1) {  // use caps if shift is held down
                                putch(kbdcaps[scancode]);
                           }
                 } else {
                       if (showkeypresses==1) {  // otherwise use normal lowercase letters
                            putch(kbd[scancode]); }
                 }
    }
}
}
}

Code: Select all

If a key was released:
  check if the released key was SHIFT, CTRL, or ALT
  if so, set the it's variable to 0.
If a key was pressed:
  check if SHIFT, CTRL, or ALT were pressed.  if so:
     set the key's variable to 1.
  otherwise:
    if shift is pressed display using the caps layout
    if alt is pressed display nothing at all
    if ctrl is pressed display nothing at all