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How to Write function in Assemble and interface to C code

Mahesh M

Please give some example that will show how write and interface assembly function to C

  • 0 in reply to Per Westermark

    We cannot add inline assembly for ARM cortex M0 ,
    main.c(204): error: #1113: Inline assembler not permitted when generating Thumb code
    below piece of code give error because naked attribute is not in KEIL ARM

    void NMI_Handler(void) __attribute__ (( naked ));
void NMI_Handler(void)
{
        /* Re-direct interrupt, get handler address from application vector table */
        asm volatile("ldr r0, =0x1008");
        asm volatile("ldr r0, [r0]");
        asm volatile("mov pc, r0");
}

  • 0 in reply to Mahesh M

    You can use the embedded assembly:

    __asm void NMI_Handler(void)
{
  /* Re-direct interrupt, get handler address from application vector table */
  ldr r0, =0x1008
  ldr r0, [r0]
; mov pc, r0        ; deprecated
  bx  r0
}

  • 0 in reply to Robert  

    Thanks Robert
    I have one more doubt

    As per some document reference that I found on net the expected vector table generated by assembler is give below

    __Vectors       DCD     __initial_sp              ; Top of Stack
                DCD     Reset_Handler             ; Reset Handler
                DCD     NMI_Handler               ; NMI Handler
                [...more vectors...]

    00000000   LDR   PC, =__initial_sp
00000004   LDR   PC, =Reset_Handler
00000008   LDR   PC, =NMI_Handler

    but if we see actual code, it will be like

    
0x00000000 0268      LSLS     r0,r5,#9
0x00000002 1000      ASRS     r0,r0,#0
0x00000004 0169      LSLS     r1,r5,#5
0x00000006 0000      MOVS     r0,r0
0x00000008 0171      LSLS     r1,r6,#5
0x0000000A 0000      MOVS     r0,r0
0x0000000C 0173      LSLS     r3,r6,#5
0x0000000E 0000      MOVS     r0,r0

    Any idea where will be the vector table?

    Thanks

  • 0 in reply to Mahesh M 

    00000000   LDR   PC, =__initial_sp
---> 4 Bytes
00000004   LDR   PC, =Reset_Handler
00000008   LDR   PC, =NMI_Handler
======================================
0x00000000 0268      LSLS     r0,r5,#9
---> 2 Bytes
0x00000002 1000      ASRS     r0,r0,#0
0x00000004 0169      LSLS     r1,r5,#5
0x00000006 0000      MOVS     r0,r0
0x00000008 0171      LSLS     r1,r6,#5
0x0000000A 0000      MOVS     r0,r0
0x0000000C 0173      LSLS     r3,r6,#5
0x0000000E 0000      MOVS     r0,r0

  • 0 in reply to John Linq

    Again, the Vector Table contains addresses; not instructions - see your other thread about the Vector Table: http://www.keil.com/forum/19073/

  • 0 in reply to Mahesh M

    What document, exactly?

    Always give a link, so that people can check that it's a good document, and/or that you are correctly interpreting what it says.

    Beware of just implicitly trusting everything you find on the net - always verify it against "official" documentation!