PowerPC BSP mvme5500 and hardfloat.
Kate Feng
kate007.feng at gmail.com
Thu Dec 12 15:44:21 UTC 2013
Hi Joel,
I understood what you tried to point out about the surprise from the
compiler. The ISR is supposed to be written as short as possible
to the point that only a few hardware registers are needed to be
programmed. All the non-essential stuff (e.g. a = b; where a, b are
struct timespec) can be done via the rtems_event_send(), which is
implemented outside the ISR. Look at the BSP code in GT64260eth_isr() of
network/if_100MHz/GT64260eth.c and i82544EI_isr() of
network/if_1GHz/if_wm.c. Did you see that any surprise could be
triggered by the modern compiler ? If it does, then either the code
should be rewritten or there is a bug in the compiler.
BTW, which version of gcc compiler do you mean ?
Cheers,
Kate Feng
On Thu, Dec 12, 2013 at 9:35 AM, Joel Sherrill <Joel.Sherrill at oarcorp.com>wrote:
>
> On Dec 12, 2013 6:25 AM, Matt Wette <mwette at alumni.caltech.edu> wrote:
> >
> > But if you don't use FP in ISR you still need to compile the ISR with
> -fsoft-float because the compiler may dirty the FP registers otherwise.
> > For example: a = b; where a, b are struct timespec may be implemented in
> FP registers.
>
> Agreed and that is what I was trying to.point out. If FPU usage by the
> compiler is implicit and surprising, then you have to be cautious in isr
> and driver code.
>
> The larger issue is that if this setting is in the BSP's .cfg file, it
> impacts all user, rtems and bsp code. If desirable, it should be added as
> an extra addition in Makefile.am for the BSP so its impact is limited to
> the bsp.
>
> >
> > On Dec 11, 2013, at 9:44 PM, Kate Feng <kate007.feng at gmail.com> wrote:
> >
> >> Using -msoft-float is slower than using the hardware FPU.
> >> The former one will kill real-time performance. -msoft-float is not
> >> recommended to be used at the BSP level, unless the board does not
> >> support hardware FP registers. See more below......
> >>
> >> On Tue, Dec 10, 2013 at 12:36 PM, Joel Sherrill <
> Joel.Sherrill at oarcorp.com> wrote:
> >>>
> >>> GCC for the PowerPC will use floating point registers when you don't
> expect. Because of this all tasks are implicitly float on PPC. But in the
> bsp, there is concern for accidentally using the FPU in an ISR. This may be
> the sole reason soft float is used here.
> >>
> >> If the usage of the FPU could not be avoided in an ISR, then one
> >> should explicitly save and restore the FP registers in the ISR.
> >>
> >> Cheers,
> >> Kate Feng
> >>>
> >>> Would love to hear from Kate or another PowerPC BSP folks.
> >>>
> >>> On Dec 10, 2013 9:05 AM, Chirayu Desai <chirayudesai1 at gmail.com>
> wrote:
> >>> Sorry for not being clear earlier, I want to know whether -msoft-float
> is required or not.
> >>> If someone using the git HEAD (or RTEMS 4.10 or above) can verify that
> it is working without a problem, that would be great.
> >>> -msoft-float was removed in rtems.git
> commit 7425411ff581a8f5c92a1266085e7eb1f4debd2b,
> >>>
> >>>
> >>> On 10 December 2013 22:29, Chirayu Desai <chirayudesai1 at gmail.com
> > wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> https://www.rtems.org/bugzilla/show_bug.cgi?id=1323
> >>>> There is still an uncertainty regarding that bug, as the hardware
> does have a FPU, but looks like it was removed for some reason.
> >>>>
> >>>> git says this was introduced by commit
> ee732739bf9021a7a22de95eca9095c49b1d9169
> >>>>
> >>>>
> >>>>
> >>>> commit ee732739bf9021a7a22de95eca9095c49b1d9169
> >>>>
> >>>> Author: Joel Sherrill <joel.sherrill at OARcorp.com>
> >>>>
> >>>> Date: Thu Sep 13 14:26:24 2007 +0000
> >>>>
> >>>>
> >>>>
> >>>> 2007-09-07 Kate Feng <feng1 at bnl.gov>
> >>>>
> >>>>
> >>>>
> >>>> * ChangeLog, Makefile.am, README, README.booting, README.irq,
> >>>>
> >>>> preinstall.am, GT64260/MVME5500I2C.c, include/bsp.h,
> irq/irq.c,
> >>>>
> >>>> irq/irq.h, irq/irq_init.c, pci/detect_host_bridge.c,
> pci/pci.c,
> >>>>
> >>>> pci/pci_interface.c, pci/pcifinddevice.c, start/preload.S,
> >>>>
> >>>> startup/bspclean.c, startup/bspstart.c,
> startup/pgtbl_activate.c,
> >>>>
> >>>> startup/reboot.c, vectors/bspException.h,
> vectors/exceptionhandler.c:
> >>>>
> >>>> Merge my improvements in this BSP including a new network
> >>>>
> >>>> driver for the 1GHz NIC.
> >>>>
> >>>> * network/if_100MHz/GT64260eth.c,
> network/if_100MHz/GT64260eth.h,
> >>>>
> >>>> network/if_100MHz/GT64260ethreg.h,
> network/if_100MHz/Makefile.am,
> >>>>
> >>>> network/if_1GHz/Makefile.am, network/if_1GHz/POSSIBLEBUG,
> >>>>
> >>>> network/if_1GHz/if_wm.c, network/if_1GHz/if_wmreg.h,
> >>>>
> >>>> network/if_1GHz/pci_map.c, network/if_1GHz/pcireg.h: New
> files.
> >>>>
> >>>>
> >>>> Anybody here who can test this on actual hardware and verify what is
> wrong with this?
> >>>>
> >>>>
> >>>> Thanks.
> >>>>
> >>>> Chirayu Desai
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> rtems-users mailing list
> >>> rtems-users at rtems.org
> >>> http://www.rtems.org/mailman/listinfo/rtems-users
> >>>
> >>
> >> _______________________________________________
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> >> rtems-users at rtems.org
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> >
> >
>
>
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