Re: TARGET_FPU not getting populated for powerpc 405/440 fpu-hard targets

[Mark Hatle <mark.hatle@windriver.com>]

On 8/24/12 11:49 AM, Elvis Dowson wrote:
> Hi Khem,
>
> On Aug 24, 2012, at 8:35 PM, Khem Raj wrote:
>
>> On Fri, Aug 24, 2012 at 9:27 AM, Elvis Dowson <elvis.dowson@gmail.com
>> <mailto:elvis.dowson@gmail.com>> wrote:
>>> I just observed that TARGET_FPU is not getting populated, when you do
>>> a build for fpu-hard targets. For fpu-soft targets, it displays TARGET_FPU =
>>> "soft", but for fpu-hard targets, it display TARGET_FPU = "".
>>
>> that means default is hard for this architecture. This option is
>> essentially used to configure gcc
>> unless your fpu is special like fsl one's you are good here.
>
> The FPU unit is an IP core, that is attached to a generic PowerPC405 or
> PowerPC440 embedded processor core on the FPGA, which by default doesn't contain
> an FPU unit.
>
> In the Xilinx FPGA hardware project, I have to add this FPU unit, and there are
> some additional options that I can see relevant to this setup with the FPU unit,
> such as -mxilinx-fpu and -mfpu=dp_full
>
> Should I specify them in TUNE_CCARGS (as shown below)
> or TUNE_FEATURES_tune-ppc405e (not done below) or specify the same values for
> both variables ?
>
> TUNE_CCARGS += "${@bb.utils.contains("TUNE_FEATURES", "ppc405e", "-mcpu=405fp
> -mxilinx-fpu -mfpu=dp_full", "", d)}"
>
> AVAILTUNES += "ppc405e"
> TUNE_FEATURES_tune-ppc405e = "m32 ppc405e fpu-hard"

fpu-hard is the classic PowerPC FPU unit.  If that is what these ip blocks 
implement then there is nothing further required.

If the unit does NOT include a classic PowerPC FPU, then you should not be using 
fpu-hard.

If it -also- implements additional FPU instructions via the -m...fpu stuff 
specific to the IP blocks, then that is where the target_fpu comes in and some 
other changes will be necessary.... It's been a while since I worked through 
this, but the e500 stuff may be a reasonable example of how to implement it.

--Mark

> Best regards,
>
> Elvis Dowson
>
>
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