I am currenlty working on a xv6, I want to add an option when left shift + arrow up is pressed to return previously used command, something like history. I need help figuring out how to read when left shift is pressed
console.c file

#define BACKSPACE 0x100
#define CRTPORT   0x3d4
#define KEY_UP 0xE2
#define k 0x1C4
#define KEY_DN 0xE3
#define SHIFT 0x2A
#define CAPSLOCK 0x3A
int color = 0x0700;
static int flagShift = 0;
static ushort *crt = (ushort*)P2V(0xb8000);  // CGA memory

static void
cgaputc(int c)
{
    int pos;
    int color = 0x0700;

    // Cursor position: col + 80*row.
    outb(CRTPORT, 14);
    pos = inb(CRTPORT+1) << 8;
    outb(CRTPORT, 15);
    pos |= inb(CRTPORT+1);


    if(c == 'n'){
        pos += 80 - pos%80;
        //cprintf("1");
    }else if(c == BACKSPACE){
        if(pos > 0) --pos;

    }else if(c == SHIFT){
        flagShift = 1;
    }else{
       if(flagShift == 0){
        crt[pos++] = (c&0xff) | color;  // black on white
       }else{
         crt[pos++] = (c&0xff) | 0x0000;
       }

    }

    if(pos < 0 || pos > 25*80){
        panic("pos under/overflow");
    }
    if((pos/80) >= 24){  // Scroll up.
        memmove(crt, crt+80, sizeof(crt[0])*23*80);
        pos -= 80;
        memset(crt+pos, 0, sizeof(crt[0])*(24*80 - pos));
    }

    outb(CRTPORT, 14);
    outb(CRTPORT+1, pos>>8);
    outb(CRTPORT, 15);
    outb(CRTPORT+1, pos);
    crt[pos] = ' ' | 0x0700;
}

Shift map in kbd.h

#define SHIFT           (1<<0)
static uchar shiftcode[256] =
{
    [0x1D] CTL,
    [0x2A] SHIFT,
    [0x36] SHIFT,
    [0x38] ALT,
    [0x9D] CTL,
    [0xB8] ALT
};
static uchar shiftmap[256] =
{
    NO,   033,  '!',  '@',  '#',  '$',  '%',  '^',  // 0x00
    '&',  '*',  '(',  ')',  '_',  '+',  'b', 't',
    'Q',  'W',  'E',  'R',  'T',  'Y',  'U',  'I',  // 0x10
    'O',  'P',  '{',  '}',  'n', NO,   'A',  'S',
    'D',  'F',  'G',  'H',  'J',  'K',  'L',  ':',  // 0x20
    '"',  '~',  NO,   '|',  'Z',  'X',  'C',  'V',
    'B',  'N',  'M',  '<',  '>',  '?',  NO,   '*',  // 0x30
    NO,   ' ',  NO,   NO,   NO,   NO,   NO,   NO,
    NO,   NO,   NO,   NO,   NO,   NO,   NO,   '7',  // 0x40
    '8',  '9',  '-',  '4',  '5',  '6',  '+',  '1',
    '2',  '3',  '0',  '.',  NO,   NO,   NO,   NO,   // 0x50
    [0x9C] 'n',      // KP_Enter
    [0xB5] '/',       // KP_Div
    [0xC8] KEY_UP,    [0xD0] KEY_DN,
    [0xC9] KEY_PGUP,  [0xD1] KEY_PGDN,
    [0xCB] KEY_LF,    [0xCD] KEY_RT,
    [0x97] KEY_HOME,  [0xCF] KEY_END,
    [0xD2] KEY_INS,   [0xD3] KEY_DEL
};

When I tried this with capslock instead of shift capslock wasn’t working either so I guess I need help understanding how these specific buttons work.