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Asked: 2026-05-13T12:11:28+00:00

In my project I need to use inline Assembly, but it need to be

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In my project I need to use inline Assembly, but it need to be Nasm, because I’m not too much familiar with GAS.
My try:

void DateAndTime()
{
   asm
   (.l1:    mov al,10           ;Get RTC register A
    out RTCaddress,al
    in al,RTCdata
    test al,0x80            ;Is update in progress?
    jne .l1             ; yes, wait

    mov al,0            ;Get seconds (00 to 59)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeSecond],al

    mov al,0x02         ;Get minutes (00 to 59)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeMinute],al

    mov al,0x04         ;Get hours (see notes)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeHour],al

    mov al,0x07         ;Get day of month (01 to 31)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeDay],al

    mov al,0x08         ;Get month (01 to 12)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeMonth],al

    mov al,0x09         ;Get year (00 to 99)
    out RTCaddress,al
    in al,RTCdata
    mov [RTCtimeYear],al

    ret);
}

There is any way to do this but using Nasm instead of GAS?

I think I need to add a argument when compiling.

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1 Answer

  1. Editorial Team

    I did a quick google on ‘nasm + gcc’, have a look here, here, and here.

    In a nutshell the switches to be used for nasm in order to link along with the gcc compiled object is:

    nasm -f elf

    Edit: The above was absolutely irrelevant as Nathan was looking for a GAS syntax similar to the code snippet in the question..here is my attempt of the GAS’ified version…

    void DateAndTime()
{
   int RTCaddress, RTCdata, RTCtimeSecond, RTCtimeHour, RTCtimeMinute, RTCtimeDay, RTCtimeMonth, RTCtimeYear;
   // Set RTCaddress and RTCdata respectively first...
   RTCaddress = 0x70;
   RTCdata = 0x71; 
   asm
   (
.l1:    
    movb $10, %al           ;Get RTC register A
    out %al, RTCaddress        ; Think RTCaddress needs to be declared...
    in RTCdata, %al            ; RTCdata needs to be declared
    test $80, %al            ;Is update in progress?
    jne .l1             ; yes, wait

    movb $0, %al            ;Get seconds (00 to 59)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeSecond]

    movb $2, %al         ;Get minutes (00 to 59)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeMinute]

    movb $4, %al         ;Get hours (see notes)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeHour]

    movb $7, %al         ;Get day of month (01 to 31)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeDay]

    movb $8, %al         ;Get month (01 to 12)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeMonth]

    movb $9, %al         ;Get year (00 to 99)
    out %al, RTCaddress
    in RTCdata, %al
    movb %al, [RTCtimeYear]

    ret);

    Judging by the BIOS data where the RTC clock is, ports used is 0x70, 0x71 which I have used here… I may be wrong…

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