Re: Target options for gcc

Greg Ungerer wrote:
> 
> Hi David,
> 
> David Brown wrote:
>> Greg Ungerer wrote:
>>> Hi Bob,
>>>
>>> Bob Brusa wrote:
>>>> On Tue, 08 Jan 2008 17:43:24 +0100, Seymour David 
>>>> <[email protected]> wrote:
>> <snip>
>>> Traditionally the uClinux kernel for the 5282 has used the -m5307
>>> switch - apparently its code instruction level timing tables in gcc
>>> are closer to that of the 5282 that the default -m5200 switch.
>>>
>>> But you can use -m5200 on any of the ColdFire family members.
>>>
>>>
>>>>> The manufacturer of the COBRA5285-Board I am using provided 
>>>>> examples. One
>>>>> of them uses the option -m5307 which is however nowhere documented.
>>>
>>> Looks like who ever merged the gcc changes that support those
>>> newer switches didn't update the manual. Even the latest 4.2.2
>>> doco doesn't list anything other than -m5200 (it does list the
>>> other new uClinux switches like -msep-data though...).
>>>
>>
>> If you use "m68k-elf-gcc -v --help", you'll see a list of all the 
>> command line switches for the gcc you are using.  In particular, if 
>> you get a recent build from CodeSourcery, there is direct support for 
>> a wide range of Coldfires - the switch you want is "-mcpu=5282".  In 
>> keeping with many other embedded gcc ports, CodeSourcery use the 
>> "-mcpu=" flag to make it easier to choose the exact instruction set 
>> and code generation options appropriate for different devices, as well 
>> as helping to get the correct linker file and libraries for the 
>> device.  Thus you should not specify "-m" options directly, but use 
>> the "-mcpu=" for your device.
>>
>> Since CodeSourcery work on their own branches of gcc, they can get 
>> changes into the code much faster than the standard FSF gcc tree, and 
>> thus their versions have newer features.  These all get merged back to 
>> the FSF (several of the official gcc lead developers work at 
>  >
>> CodeSourcery), but because changes must be tested clean on such a 
>> range of devices, it takes much longer - the "-mcpu=" flags will be in 
>> the FSF gcc at version 4.3, while CodeSourcery has them on 4.2-47.
>>
>>
>> Incidentally, the official gnu gcc docs for 4.1.1 *are* available on 
>> the gcc website - it's just that there is no direct link from the 
>> documentation page:
>>
>> http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/
> 
> Perhaps not recommended for use, but still no versions of the
> documentation list the -mxxxx options for the 5xx. Even though
> they extensively list the other 68xxx varients.
> 
> Regards
> Greg

The CodeSourcery documentation lists all the variants (I don't think 
they have it directly accessible on-line, but you'll get it along with 
the compiler downloads).  You can also see the list in the docs for the 
development version of gcc (i.e., 4.3):

http://gcc.gnu.org/onlinedocs/gcc/M680x0-Options.html#M680x0-Options


I didn't notice before that you are Greg of SnapGear and ucLinux fame. 
How well do CodeSourcery's compilers work with ucLinux?  I've only used 
them for stand-alone ColdFire development, but hope to test out ucLinux 
before too long.

mvh.,

David

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