rtems floating poing switch

https://lists.rtems.org/pipermail/users/2019-December/067321.html

Hello, world


I have a question about the use of trap 4 by RTEMS on Sparc32 (leon3).
Since our app needs FP, we set the PSR[EF] bit during the boot process before RTEMS is invoked.
Since we don't expect the fp_disabled trap (4) to occur, we install a fatal handler for it with
rtems_interrupt_catch(&fatalTrapHandler, 4, &old);

However, the fatalTrapHandler is invoked a short time after application start (we use the Init() task
and start a handful of additional tasks, all of which have attribute RTEMS_FLOATING_POINT)
and the PSR[EF] bit is indeed cleared. None of our tasks
clears that bit, so we suspect RTEMS does it for some reason.

Question: is an RTEMS/sparc application allowed to install a handler for trap 4? I could not find an
answer in the docs for SPARC Specific Information.

Thanks for any insight!
Regards, Jens


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#if defined(SPARC_USE_LAZY_FP_SWITCH)
  FPDIS_TRAP(SYM(syscall_lazy_fp_switch));      ! 04 fp disabled
40000040:a1 48 00 00 rd  %psr, %l0
40000044:29 10 00 bd sethi  %hi(0x4002f400), %l4
40000048:81 c5 22 00 jmp  %l4 + 0x200! 4002f600 <syscall_lazy_fp_switch>
4000004c:27 00 00 04 sethi  %hi(0x1000), %l3
#else
  BAD_TRAP;                                     ! 04 fp disabled
#endif

源码目录下有sparc相关的内容：

rtems-4.6.0csrcliblibbspsparcshared

E:projectobsw tems-4.6.0cpukitscorecpusparccpu.c

_CPU_Initialize

_CPU_ISR_install_vector

_CPU_Context_Initialize