How to access GBA RTC

#include <gba_console.h>
#include <gba_interrupt.h>
#include <gba_systemcalls.h>
#include <stdio.h>
#include <stdlib.h>

void enableRTC(u16 n){*(vu16*)0x80000c8=n;}
void setRTCwritemode(u16 n){*(vu16*)0x80000c6=n;}//0=read, 2=write
void setRTCcommand(u8 command){
    *(vu16*)0x80000c4=1; //initialize
    *(vu16*)0x80000c4=5; //start sending
    *(vu16*)0x80000c4=0;
    int i=0;for(;i<8;i++){
        *(vu16*)0x80000c4=((command>>(7-i))<<1)|1; //send from upper bit
        *(vu16*)0x80000c4=0;
    }
}
u8 getRTCbyte(){
    u8 ret=0;
    int i=0;for(;i<8;i++){
        *(vu16*)0x80000c4=2|1;
        ret|=(((u8)(*(vu16*)0x80000c4)&2)>>1) << i; //sent from lower bit
        *(vu16*)0x80000c4=0;
    }
    return (ret/16*10)+ret%16;
}

int main(){
    irqInit();
    irqEnable(IRQ_VBLANK);
    consoleDemoInit();

    enableRTC(1);
    setRTCwritemode(0);
    setRTCcommand(0x65);
    iprintf("---%u/%02u/%02u %d %02d:%02d:%02d---\n",getRTCbyte()+1900+100,getRTCbyte(),getRTCbyte(),getRTCbyte(),getRTCbyte(),getRTCbyte(),getRTCbyte());

    while(1){VBlankIntrWait();}
}