Re: WG: Re: motorRecord on linux-arm

[Ron Sluiter <sluiter@aps.anl.gov>]

I have checked Jens's motor.h changes into the motor module SVN trunk. Those changes will appear in the next release; R6.9

Ron

On 6/2/2014 2:28 AM, Torsten Bögershausen wrote:

On 2/7/14 18:02, Jens.Eden@ptb.de wrote:

Am 07.02.2014 16:56, schrieb Ron Sluiter:

On 2/7/2014 9:21 AM, Jens.Eden@ptb.de wrote:

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)

Thanks for the suggestion but MSB_First/LSB_First is set to indicate how

C/C++ bit fields are packed, not endianness.

To my knowledge and experience
(arm gcc & RVCT, x86 gcc & MSVC, powerpc gcc, sparc gcc) the compiler fills
a bitfield with bits the same way it fills a machine word with bytes.
In other words: the endianess for bits and bytes is the same, either big or little.

Is there any chance to get Jens patch into motor.h ?
Either the short one (my favorite) or the long one ?

What compiler and compiler version are you using?

I verified with the following compilers:
Linux 32bit/64bit (gcc4.7.4)
linux arm gcc-Version 4.7.2 20120731 (prerelease) (crosstool-NG
linaro-1.13.1+bzr2458 - Linaro GCC 2012.08)
powerpc-rtems4.10.2 (mvme2100 cpu=603e)
tornado-2.2 (CPU=MC68040)

At least for gcc bit field packing is LSB_first for little endian and
MSB_first for big endian machines.

If you are afraid of breaking existing code, how about this:

#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 defined(ppc603e)
      #define MSB_First (TRUE)  /* MSB is packed first. */
#elif defined(CPU) && ((CPU == PPC604) || (CPU == PPC603) || (CPU ==
PPC85XX) || (CPU == MC68040) || (CPU == PPC32))
      #define MSB_First (TRUE)  /* MSB is packed first. */
#elif defined(__GNUC__)
      #include <epicsEndian.h>
      #if (EPICS_BYTE_ORDER == EPICS_ENDIAN_LITTLE)
          #define LSB_First (TRUE)
      #else
          #define MSB_First (TRUE)
      #endif
#else
      #error: unknown bit order!
#endif

Jens