Re: [avr-chat] How to stop avr-gcc from replacing my code with ellipsis

[Omar Choudary]

Thanks a lot.

Yes David, that is exactly what I needed.

I don't really need a delay, I am interested in doing some power
measurements and therefore I want a precise sequence of instructions,
including NOPs.

I have been using both assembler inlined in C code and an aseembler
file. The code I shown earlier was from an assembler (.S) file,
compiled with avr-gcc.
The listing file is generated by applying avr-objdump on the resulting
.elf file.

With the --disassemble-zeros switch I get what I want:
4dac:   2f 93           push    r18
    4dae:   2f b7           in  r18, 0x3f   ; 63
    4db0:   f8 94           cli
    4db2:   00 00           nop
    4db4:   00 00           nop
    4db6:   00 00           nop
    4db8:   00 00           nop
    4dba:   00 00           nop
    4dbc:   00 00           nop
    4dbe:   00 00           nop
    4dc0:   00 00           nop
    4dc2:   00 00           nop
    4dc4:   00 00           nop
    4dc6:   86 9a           sbi 0x10, 6 ; 16
    4dc8:   8e 9a           sbi 0x11, 6 ; 17
    4dca:   00 00           nop
    4dcc:   00 00           nop
    4dce:   00 00           nop
    4dd0:   00 00           nop
    4dd2:   00 00           nop
    4dd4:   00 00           nop
    4dd6:   00 00           nop
    4dd8:   00 00           nop
    4dda:   00 00           nop
    4ddc:   00 00           nop
    4dde:   2f bf           out 0x3f, r18   ; 63
    4de0:   2f 91           pop r18
    4de2:   08 95           ret

Using inline assembler it seems that I also get what I wanted:
asm volatile("nop\n\t"
     d34:   00 00           nop
     d36:   00 00           nop
     d38:   00 00           nop
     d3a:   00 00           nop
     d3c:   00 00           nop
     d3e:   00 00           nop
     d40:   00 00           nop
                 "nop\n\t"
                 "nop\n\t"
                 ::);

   asm volatile("sbi %[port], %[bit]"  "\n\t"
     d42:   86 9a           sbi 0x10, 6 ; 16
                 :/* NO OUTPUTS */
                 :[port] "I" (_SFR_IO_ADDR(VPORT0.DIR)), [bit] "I" (PIN6_bp)
                );
    asm volatile("sbi %0, %1"   "\n\t"
     d44:   8e 9a           sbi 0x11, 6 ; 17
                 :/* NO OUTPUTS */
                 :"I" (_SFR_IO_ADDR(VPORT0.OUT)), "I" (PIN6_bp)
                );

    asm volatile("nop"::);
     d46:   00 00           nop
    asm volatile("nop"::);
     d48:   00 00           nop
    asm volatile("nop"::);
     d4a:   00 00           nop
    asm volatile("nop"::);
     d4c:   00 00           nop
}
     d4e:   08 95           ret

I feel that for my purposes using the assembler file seems clearer,
but it looks like both approaches are equally fine.

Thanks,
 Omar

On Mon, May 21, 2012 at 8:23 PM, Weddington, Eric
<address@hidden> wrote:
>
>
>> -----Original Message-----
>> From: address@hidden [mailto:avr-chat-
>> address@hidden On Behalf Of David Kelly
>> Sent: Monday, May 21, 2012 1:20 PM
>> To: address@hidden
>> Subject: Re: [avr-chat] How to stop avr-gcc from replacing my code with
>> ellipsis
>>
>>
>> On May 21, 2012, at 1:43 PM, Weddington, Eric wrote:
>>
>> > Hi Omar,
>> >
>> > How are you writing and compiling your code?
>>
>> He said,
>> >> However when the code is compiled I get the following in the listing
>> >> file (generated with avr-objdump):
>
> Sure, but just because somebody says it's compiled doesn't mean that it is. 
> It could have been "assembled" using the assembler directly.
>
>>
>> The NOPs are there, the addresses jump properly.
>>
>> Reading the man page for avr-objdump I suspect this is the switch he wants:
>>
>>        -z
>>        --disassemble-zeroes
>>            Normally the disassembly output will skip blocks of zeroes.  This
>>            option directs the disassembler to disassemble those blocks, just
>>            like any other data.
>>
>
> Oh, you're very probably correct! :-)
>
> Eric
>
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