Re: [avr-gcc-list] Device specific ISA support in AVR

[S, Pitchumani]

March 03, 2014 4:24 PM, Georg-Johann Lay
> Am 02/25/2014 01:05 PM, schrieb S, Pitchumani:
> > Hi,
> >
> > Few AVR Xmega devices have specific instruction support than the
> architecture
> > it belongs to. For example atxmega128b1 device has RMW instructions
> (XCH,LAC,
> > LAS and LAT) support, but not all avrxmega6 devices have.
> >
> > Now, avr-gcc passes architecture name to assembler instead of device
> name. So,
> > RMW instructions are not recognized (illegal opcode error) by assembler.
> >
> > To address this issue, we could add device specific ISA to device
> details
> > in GCC. Driver can pass additional option based on specific ISA that a
> device
> > has. Assembler can add device specific ISA to architecture ISA based on
> the
> > option it receives.
> >
> > I have attached patches for avr-gcc and avr-as to address this issue.
> >
> > device-specific-isa-avr-gcc.patch:
> > * Device specific ISA information is added to device details.
> > * avr-gcc passes -mrmw option to assembler if the selected device
> > has RMW instruction support.
> >
> > device-specific-isa-avr-as.patch:
> > * Add option -mrmw.
> > * Add AVR_ISA_RMW to current architecture ISA if -mrmw option specified.
> >
> > Please review the patches and comment.
> 
> Hi Pitchumani,
> 
> some remarks on the work:
> 
> 1) It might be useful to builtin-define macros so that user code can test
> for
> availability of these instructions, similar to __AVR_ERRATA_SKIP__ or
> __AVR_HAVE_MUL__. That way users can depend on the macro when implementing
> their inline assembler that might use RMW instructions. This macro should
> then
> be documented with the other macros.
> 
> 2) Binutils' documentation should spell out "RMW" as read-modify-store.
> It's
> always easier to remember an option if the resolution of some cryptic
> letter
> combination is known.
> 
> 3) There are also MCU-specific ISA-like features in avr-mcus.def:
> 
> *) ERRATA_SKIP (ISA with broken CPSE, SBRC/S, SBIC/S wrapping 32-bit insn)
> 
> *) SHORT_SP (MCU has no SPH special function register)
> 
> Maybe these 3 ISA properties can be merged into one field with respective
> flags.  That way avr-mcus.def would be easier to read and the number of
> fields
> would reduce.
> 
> 4) I'd prefer ISA in front of the feature, not as suffix, i.e.
> 
> AVR_ISA_RMW, AVR_ISA_SKIP_BUG, AVR_ISR_SP8, etc. instead of AVR_RMW_ISA.
> 
> 5) There is already a Binutils PR, cf. PR15043 (with differently named
> options,
> though).
> 
> http://sourceware.org/PR15043
> 
> 6) The GCC release notes must mention that at least Binutils version xyz
> is needed.
> 
> Typically, there is some time margin until GCC might assume that specific
> features are available in binutils.  This is beacuse your work is not a
> pure
> extension but affects existing devices.
> 
> 7) Don't you skip the test conditions that you want to test in the new GCC
> testsuite program? I.e. you skip -mmcu=atxmega32a4u.

Hi Johann,

I have updated avr-gcc patch as per your comments. Please review.

Regards,
Pitchumani


gcc/ChangeLog
2014-03-12  Pitchumani Sivanupandi  <address@hidden>

    * config/avr/avr-arch.h (avr_mcu_t): Add dev_specific_feature field 
    to have device specific ISA/ feature information. Remove short_sp
    and errata_skip fields.
    Add avr_device_specific_features enum to have device specific info.
    * config/avr/avr-c.c: use dev_specific_feature to check errata_skip.
      Add __AVR_ISA_RMW__ builtin macro if RMW ISA available.
    * config/avr/avr-devices.c (avr_mcu_types): Update AVR_MCU macro for
    updated device specific info.
    * config/avr/avr-mcus.def: Merge device specific details to 
    dev_specific_feature field.
    * config/avr/avr.c (avr_2word_insn_p): use dev_specific_feature field
    to check errata_skip.
    * config/avr/avr.h: same for short sp info.
    * config/avr/driver-avr.c (avr_device_to_as): Pass -mrmw option to
    assembler if RMW isa supported by current device.
    * config/avr/genmultilib.awk: Update as device info structure changed.
    * doc/invoke.texi: Add info for __AVR_ISA_RMW__ builtin macro

gcc/testsuite/ChangeLog
2014-03-12 Pitchumani Sivanupandi  <address@hidden>

    * gcc.target/avr/ dev-specific-rmw.c: New test.

dev-specific-feature-avr-gcc.patch
Description: dev-specific-feature-avr-gcc.patch