possible SPARC cpu_asm.S error

[Jiri Gaisler]

In my opinion, the nops are not needed since only global registers
are used in the  sequence:

        mov     %g1, %psr                     ! restore status register and
                                              ! **** DISABLE TRAPS ****
        mov     %wim, %g2                     ! g2 = wim
        mov     1, %g4
        sll     %g4, %g3, %g4                 ! g4 = WIM mask for CW invalid

If the problem is interrupt related, the bug might be elsewhere.

Do you have a test program that triggers the error? I have used
the rtems-ttcp networking program and sent large ping floods to
generate many interrupts, but I saw no crash.

Regarding the -mv8 option to leon3, it should not be made default.
There are leon3 systems without hardware mul/div for which this
option will not work. The kernel does not do a lot of multiplication,
so the -mv8 should only be used when compiling applications, not
the kernel.

Jiri.

Jerry Needell wrote:
> 
> I think I have found an error in the cpukit/score/cpu/sparc/cpu_asm.S
> code. When writing to the PSR, a sequence of three NOP's must be added
> to ensure that the PSR value is properly set after running through the
> pipeline. This is done in most places in cpu_asm.S but was left out in a
> few and, I think, causing me some problems. I have been trying to track
> down and intermittent crash for a long time! My application was crashing
> after servicing an interrupt. cpu_asm.S includes ISR_Dispatch which was
> missing the NOP's ater setting the PSR before returning.
> 
>    The problem became much worse when I tried rebuilding 4.6.99.3 using
> the -mcpu-v8 flag to take advantage of the SPARC V8 multiply in the
> LEON3.  The  diff attached also  has the change I made to
> make/custom/leon3.cfg to set the -mcpu=v8 switch.            The
> cpu-asm.S error should apply to all SPARC cpu's (v7 or v8).
> 
>  
> - Jerry
>  
> 
> 
> ------------------------------------------------------------------------
> 
> Index: cpukit/score/cpu/sparc/cpu_asm.S
> ===================================================================
> RCS file: /usr1/CVS/rtems/cpukit/score/cpu/sparc/cpu_asm.S,v
> retrieving revision 1.11
> diff -u -r1.11 cpu_asm.S
> --- cpukit/score/cpu/sparc/cpu_asm.S	1 Apr 2004 10:12:49 -0000	1.11
> +++ cpukit/score/cpu/sparc/cpu_asm.S	15 Aug 2006 11:47:40 -0000
> @@ -212,6 +212,7 @@
>          andn    %g1, SPARC_PSR_ET_MASK | SPARC_PSR_CWP_MASK, %g1
>          or      %g1, %g3, %g1                 ! g1 = heirs psr
>          mov     %g1, %psr                     ! restore status register and
> +	nop; nop; nop;			      ! Need three nops for pipeline 
>                                                ! **** DISABLE TRAPS ****
>          mov     %wim, %g2                     ! g2 = wim
>          mov     1, %g4
> @@ -605,6 +606,7 @@
>           */
>  
>          mov      %l0, %psr             ! **** DISABLE TRAPS ****
> +	nop; nop; nop;			      ! Need three nops for pipeline 
>  
>          /*
>           *  Decrement ISR nest level and Thread dispatch disable level.
> @@ -798,6 +800,7 @@
>  good_task_window:
>  
>          mov     %l0, %psr                  !  **** DISABLE TRAPS ****
> +	nop; nop; nop;			   ! Need three nops for pipeline 
>                                             !  and restore condition codes.
>          ld      [%g1 + ISF_G1_OFFSET], %g1 ! restore g1
>          jmp     %l1                        ! transfer control and
> Index: make/custom/leon3.cfg
> ===================================================================
> RCS file: /usr1/CVS/rtems/make/custom/leon3.cfg,v
> retrieving revision 1.2
> diff -u -r1.2 leon3.cfg
> --- make/custom/leon3.cfg	9 Jan 2006 15:09:55 -0000	1.2
> +++ make/custom/leon3.cfg	15 Aug 2006 11:47:41 -0000
> @@ -20,7 +20,7 @@
>  # CPU_CFLAGS = -mno-v8 -mcypress $(MSOFT_FLOAT)
>  #     -mcpu=cypress says to optimize for a Cypress 60x chipset
>  #CPU_CFLAGS = -mcpu=cypress $(MSOFT_FLOAT)
> -CPU_CFLAGS = -mcpu=cypress -msoft-float
> +CPU_CFLAGS = -mcpu=v8 -msoft-float
>  
>  # optimize flag: typically -0, could use -O4 or -fast
>  # -O4 is ok for RTEMS