RE: [patch,avr] Device specific instructions support for avr

["S, Pitchumani" <Pitchumani dot S at atmel dot com>]

Hi Denis,

> -----Original Message-----
> From: Denis Chertykov [mailto:chertykov@gmail.com]
> Sent: Monday, March 03, 2014 10:45 PM
> 2014-03-03 13:34 GMT+04:00 S, Pitchumani <Pitchumani.S@atmel.com>:
> > 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.
> >
> > 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.
> 
> I don't like additional option '-mrmw' because we already have a way
> for passing device specific ISA.
> IMHO better to add new avr_arch (ie atxmega128b1 is ARCH_AVRXMEGA6U)
> GAS already have AVR_ISA_XMEGAU for RMW instructions.

New avr_arch can be added. But there are devices in avrxmega2, 4, 5, 6 and 7
architectures which has rmw instructions. In this case, new architecture required 
for above variants as well. Also there is DES instruction which is available only 
for few avr devices. So, I thought adding an option will avoid creating many new 
architectures.

Related binutils PR: http://sourceware.org/PR15043
Related discussion: http://lists.nongnu.org/archive/html/avr-gcc-list/2014-03/msg00000.html

Please suggest.

Regards,
Pitchumani