Re: Target options for gcc

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/


mvh.,

David
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