x86-bare-metal-examples/rtc.S

/* TODO what do those numbers mean? Where is this all documented? */
.equ RTCaddress, 0x70
.equ RTCdata, 0x71

#include "common.h"
BEGIN

update_in_progress:
    mov $10, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    testb $0x80, %al
    jne update_in_progress

    /* Second. */
    mov $0, %al
    out %al, $RTCaddress
    in $RTCdata, %al

    /* Only print if second changed. */
    cmp %al, %cl
    je update_in_progress
    mov %al, %cl

    PRINT_HEX <%al>
    PUTC

    /* Minute. */
    mov $0x02, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    PRINT_HEX <%al>
    PUTC

    /* Hour. */
    mov $0x04, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    PRINT_HEX <%al>
    PUTC

    /* Day. */
    mov $0x07, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    PRINT_HEX <%al>
    PUTC

    /* Month. */
    mov $0x08, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    PRINT_HEX <%al>
    PUTC

    /* Year. */
    mov $0x09, %al
    out %al, $RTCaddress
    in $RTCdata, %al
    PRINT_HEX <%al>
    PRINT_NEWLINE

    jmp update_in_progress