Re: motorRecord on linux-arm

[Till Straumann <strauman@slac.stanford.edu>]

Shudder!

If you absolutely have to test for endianness w/o external help
then let the compiler figure it out, e.g., like this:


int
is_little_endian()
{
const union {
    unsigned short us;
    unsigned char  uc[2];
} tester = { us: 1 };
    return !! tester.uc[0];
}

rather than getting lost in a maze of #ifdefs

FWIW: gcc will optimize all of this away and just use the appropriate result
which is known at compile time.

- Till

On 02/07/2014 07:21 AM, Jens.Eden@ptb.de wrote:
> I recently tried to run a motor on a Raspberry Pi and found that the DMOV
> field would never
> return to 1 after the move completed. The reason is, that the following
> cpu-architecture
> switch in motor.h doesn't have an entry for armv6
>
> #if defined(_WIN32) || defined(_M_IX86) || defined(_X86_)
>      #define LSB_First (TRUE)  /* LSB is packed first. */
> #elif defined(__i386__) || defined(_armv4l_) || defined(_X86_64_) ||
> defined(__APPLE__)
>      #define LSB_First (TRUE)  /* LSB is packed first. */
> #elif defined(i386)
>      #define LSB_First (TRUE)  /* LSB is packed first. */
> #elif defined(sparc) || defined(m68k) || defined(powerpc)
>      #define MSB_First (TRUE)  /* MSB is packed first. */
> #elif (CPU == PPC604) || (CPU == PPC603) || (CPU == PPC85XX) || (CPU ==
> MC68040) || (CPU == PPC32)
>      #define MSB_First (TRUE)  /* MSB is packed first. */
> #else
>      #error: unknown bit order!
> #endif
>
> Since (CPU == PPC604) is true for all cases where CPU is undefined, the
> arm compiler did not
> fall through to the error message in the else case.
>
> I suggest to remove the switch and replace the occurrence of  MSB_First
> with the EPICS
> provided endianness switch:
> +#include <epicsEndian.h>
>
> -#ifdef MSB_First
> +#if (EPICS_BYTE_ORDER == EPICS_ENDIAN_BIG)
>
> Jens