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Subject: Re: Linus: bootloader main.c,1.17,1.18

Re: Linus: bootloader main.c,1.17,1.18

From: Dave Hooper <dave_at_beermex.com>
Date: 2005-07-12

Interesting point (good link by the way - I'll have to make a note of
that). I wonder if the default optimisation flags for rockbox build
(just -O) does not pick up this optimisation, but a higher-level
optimisation (e.g -O3) would do? Just a thought anyway..

----- Original Message -----
From: "Ronald Teune" <rtwolf@gmx.net>
To: "Rockbox development" <rockbox@cool.haxx.se>
Sent: Tuesday, July 12, 2005 2:12 PM
Subject: Re: Linus: bootloader main.c,1.17,1.18

> Hi Dave,
>
> neat, thanks. Odd that gcc doesn't do such a simple optimisation.
> Btw, if anyone else on the list doesn't know what atomic is, here's a
> clear description:
> http://www-128.ibm.com/developerworks/library/pa-atom/
>
> Ronald
>
> On Tue, 12 Jul 2005 14:51:46 +0200, <dave@beermex.com> wrote:
>
>> Hi Ronald;
>>
>> or_l is not a function call - it compiles to inline code (i.e. no
>> CALL/RETURN, the body is actually applied in-place)
>>
>> Furthermore, or_l is actually optimised assembler (just one assembly
>> instruction!) whereas the C code "X |= Y" compiles to two assembly
>> instructions, which is slower and also not atomic
>>
>> Regards,
>> d
>>
>>> Hi,
>>>
>>>> and_l(~0x01000000, &GPIO_OUT); -> /* GPIO24 is the Cypress chip
>>>> power */
>>>> GPIO_ENABLE |= 0x01000000; -> or_l(0x01000000, &GPIO_ENABLE);
>>>> GPIO_FUNCTION |= 0x01000000; -> or_l(0x01000000, &GPIO_FUNCTION);
>>>
>>> Not that I'm very into the rockbox code not deep c programming, but I'm
>>> curious about the above code change. It seems to me that the original
>>> code
>>> (left) is more like standard c and probably faster (no function calls).
>>> Can someone enlighten me on this one?
>>>
>>> Ronald
> _______________________________________________
> http://cool.haxx.se/mailman/listinfo/rockbox
>

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Received on Tue Jul 12 23:45:37 2005


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