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Why is there a CLI in this function?

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alank2

Posted: Feb 12, 2012 - 10:47 PM

Joined: Jul 16, 2009
Posts: 1579

Hi,

Code:

unsigned char Compare(struct AnalyzeType *AFirst, struct AnalyzeType *ASecond)

  {

    unsigned long ul1;

    unsigned long long ull1,ull2;

    unsigned char dp1,dp2;

    if (AFirst->result>ASecond->result)

      return COMP_MORE;

    if (AFirst->result<ASecond->result)

      return COMP_LESS;

    if (AFirst->result==RESULT_UL || AFirst->result==RESULT_OL)

      return COMP_EQUAL;

    ull1=AFirst->frequency;

    dp1=AFirst->dp;

    ull2=ASecond->frequency;

    dp2=ASecond->dp;

    while (dp1<dp2)

      {

        ul1=1;

        while (dp1<dp2 && ul1<1000000000)

          {

            ul1*=10;

            dp1++;

          }

        ull1*=ul1;

      }

    while (dp2<dp1)

      {

        ul1=1;

        while (dp2<dp1 && ul1<1000000000)

          {

            ul1*=10;

            dp2++;

          }

        ull2*=ul1;

      }

    if (ull1>ull2)

      return COMP_MORE;

    if (ull1<ull2)

      return COMP_LESS;

    return COMP_EQUAL;

  }

From the LSS there is a CLI at 77a:

Code:

unsigned char Compare(struct AnalyzeType *AFirst, struct AnalyzeType *ASecond)

  {

     74e:   2f 92          push   r2

     750:   3f 92          push   r3

     752:   4f 92          push   r4

     754:   5f 92          push   r5

     756:   6f 92          push   r6

     758:   7f 92          push   r7

     75a:   8f 92          push   r8

     75c:   9f 92          push   r9

     75e:   af 92          push   r10

     760:   bf 92          push   r11

     762:   cf 92          push   r12

     764:   df 92          push   r13

     766:   ef 92          push   r14

     768:   ff 92          push   r15

     76a:   0f 93          push   r16

     76c:   1f 93          push   r17

     76e:   df 93          push   r29

     770:   cf 93          push   r28

     772:   cd b7          in   r28, 0x3d   ; 61

     774:   de b7          in   r29, 0x3e   ; 62

     776:   2e 97          sbiw   r28, 0x0e   ; 14

     778:   0f b6          in   r0, 0x3f   ; 63

     77a:   f8 94          cli

     77c:   de bf          out   0x3e, r29   ; 62

     77e:   0f be          out   0x3f, r0   ; 63

     780:   cd bf          out   0x3d, r28   ; 61

     782:   fc 01          movw   r30, r24

     784:   7b 01          movw   r14, r22

Is this related to this mystery?

Code:

static __inline__ void __iSeiParam(const uint8_t *__s)

{

    sei();

Why are interrupts being disabled for a function call?

Thanks,

Alan

sternst

Posted: Feb 12, 2012 - 10:54 PM

Joined: Jul 23, 2001
Posts: 2438
Location: Osnabrueck, Germany

Quote:

Why are interrupts being disabled for a function call?

The function uses a stack frame and manipulates the stack pointer for that purpose. This manipulation is not atomic and therefore needs to be protected. Interrupts are disabled for only 2 clock cycles.

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Stefan Ernst

alank2

Posted: Feb 12, 2012 - 11:04 PM

Joined: Jul 16, 2009
Posts: 1579

Hi,

I see, thanks for the information!

Thanks,

Alan

SprinterSB

Posted: Feb 12, 2012 - 11:09 PM

Joined: Dec 21, 2006
Posts: 1483
Location: Saar-Lor-Lux

Notice that IRQ status is restored by OUT 0x3f,*
0x3f is SREG.

You get more information by studying the assembler output instead of disassembly: The compiler prints the more enlightning

Code:

in __tmp_reg__,__SREG__

cli

out __SP_H__,r29

out __SREG__,__tmp_reg__

out __SP_L__,r28

Notice that setting I in SREG has a latency of 1 instruction in non-XMEGA — no matter if that happens by SEI, OUT, ST* or RETI.

alank2

Posted: Feb 12, 2012 - 11:17 PM

Joined: Jul 16, 2009
Posts: 1579

Hi SprinterSB,

Where is the assembler output found? Do you mean something different than the LSS file?

Thanks,

Alan

skeeve

Posted: Feb 13, 2012 - 12:19 AM

Joined: Oct 29, 2006
Posts: 2651

alank2 wrote:

Where is the assembler output found? Do you mean something different than the LSS file?

If you use -save-temps , you will get a .s file as a sibling of each .o file.

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Michael Hennebry
Iluvatar is the better part of Valar.

indianajones11

Posted: Feb 13, 2012 - 02:16 AM

Joined: Nov 28, 2004
Posts: 3552
Location: San Diego, Ca

skeeve wrote:

alank2 wrote:

Where is the assembler output found? Do you mean something different than the LSS file?

If you use -save-temps , you will get a .s file as a sibling of each .o file.

If using Studio 4 , go to Configure options -> custom settings -> "all files" and add --save-temps .

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clawson

Posted: Feb 13, 2012 - 09:48 AM

Joined: Jul 18, 2005
Posts: 62305
Location: (using avr-gcc in) Finchingfield, Essex, England

Or if using an Mfile template for foo.c use

Code:

make foo.s

to simply generate the compiler's Asm source for that file.

Whether you do this or go the --save-temps route (I use the latter) you may well find that the addition of -fverbose-asm to the CFLAGS is very enlightening as the Asm is then annotated in comments with details of the compiler's internal view of what's going on. For example:

Code:

#include <avr/io.h>

uint8_t i;

int main(void) {

  DDRB = 0xFF;

  while(1) {

    PORTB = i++;

  }

}

without -fverbose-asm:

Code:

   .file   "test.c"

__SREG__ = 0x3f

__SP_H__ = 0x3e

__SP_L__ = 0x3d

__CCP__  = 0x34

__tmp_reg__ = 0

__zero_reg__ = 1

   .text

.Ltext0:

.global   main

   .type   main, @function

main:

.LFB2:

.LM1:

/* prologue: function */

/* frame size = 0 */

.LM2:

   ldi r24,lo8(-1)

   out 55-32,r24

   lds r24,i

.L2:

.LM3:

   out 56-32,r24

   subi r24,lo8(-(1))

   rjmp .L2

.LFE2:

   .size   main, .-main

   .comm i,1,1

with -fverbose-asm:

Code:

   .file   "test.c"

__SREG__ = 0x3f

__SP_H__ = 0x3e

__SP_L__ = 0x3d

__CCP__  = 0x34

__tmp_reg__ = 0

__zero_reg__ = 1

 ;  GNU C (WinAVR 20100110) version 4.3.3 (avr)

 ;    compiled by GNU C version 3.4.5 (mingw-vista special r3), GMP version 4.2.3, MPFR version 2.4.1.

 ;  GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072

 ;  options passed:  -fpreprocessed test.i -mmcu=atmega16 -auxbase-strip

 ;  test.o -gdwarf-2 -Os -Wall -Wstrict-prototypes -std=gnu99

 ;  -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums

 ;  -fverbose-asm

 ;  options enabled:  -falign-loops -fargument-alias -fauto-inc-dec

 ;  -fbranch-count-reg -fcaller-saves -fcommon -fcprop-registers

 ;  -fcrossjumping -fcse-follow-jumps -fdefer-pop -fearly-inlining

 ;  -feliminate-unused-debug-types -fexpensive-optimizations

 ;  -fforward-propagate -ffunction-cse -fgcse -fgcse-lm

 ;  -fguess-branch-probability -fident -fif-conversion -fif-conversion2

 ;  -finline-functions -finline-functions-called-once

 ;  -finline-small-functions -fipa-pure-const -fipa-reference -fivopts

 ;  -fkeep-static-consts -fleading-underscore -fmath-errno

 ;  -fmerge-constants -fmerge-debug-strings -fmove-loop-invariants

 ;  -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls

 ;  -fpack-struct -fpeephole -fpeephole2 -freg-struct-return -fregmove

 ;  -freorder-functions -frerun-cse-after-loop -fsched-interblock

 ;  -fsched-spec -fsched-stalled-insns-dep -fsigned-zeros

 ;  -fsplit-ivs-in-unroller -fsplit-wide-types -fstrict-aliasing

 ;  -fstrict-overflow -fthread-jumps -ftoplevel-reorder -ftrapping-math

 ;  -ftree-ccp -ftree-copy-prop -ftree-copyrename -ftree-dce

 ;  -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im

 ;  -ftree-loop-ivcanon -ftree-loop-optimize -ftree-parallelize-loops=

 ;  -ftree-reassoc -ftree-salias -ftree-scev-cprop -ftree-sink -ftree-sra

 ;  -ftree-store-ccp -ftree-ter -ftree-vect-loop-version -ftree-vrp

 ;  -funit-at-a-time -fvar-tracking -fverbose-asm -fzero-initialized-in-bss

   .text

.Ltext0:

 ;  Compiler executable checksum: 61d68a374065d489330774d2533cbbdf

.global   main

   .type   main, @function

main:

.LFB2:

.LM1:

/* prologue: function */

/* frame size = 0 */

.LM2:

   ldi r24,lo8(-1)    ;  tmp47,

   out 55-32,r24    ; ,, tmp47

   lds r24,i    ;  i_lsm.7, i

.L2:

.LM3:

   out 56-32,r24    ; ,, i_lsm.7

   subi r24,lo8(-(1))    ;  i_lsm.7,

   rjmp .L2    ; 

.LFE2:

   .size   main, .-main

   .comm i,1,1

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