Historical info (2012) says xchd is not used by sdcc for mcs51. https://sourceforge.net/p/sdcc/discussion/1864/thread/08531ab9/
Regards, Xiaofan On Wed, 28 Jul 2021, 1:49 am , <theo_sd...@borm.org> wrote: > Hi, > > Currently I'm looking at making a sparse hardware re-implementation of > an mcs51-like core. It does not have to be 100% binary compatible as > long as it can run compiled C code. > > Two opcodes are a nuisance to implement in hardware: > > 0xd6/0xd7: XCHD A,(Rx) > > these opcodes take the place of what *logically* should have been the > following instructions: > > 0xd6/0xd7: DJNZ (Rx),offset > > Though I guess the XCHD opcodes had some use "back in the day", the DJNZ > opcodes make more sense to me, and are much less effort to implement. > Actually, they come for free while implementing XCHD is a special case > in an otherwise mostly regular part of the opcode array. (There are some > other instructions that are in odd positions imho) > > I've grepped my way through the sources, and found few references to > xchd, and my impression is that these instructions will never be > emitted, but I'd appreciate some expert input: > > Does the mcs51 backend ever emit XCHD instructions? > > > with kind regards, > > > Theo > > > > _______________________________________________ > Sdcc-user mailing list > Sdcc-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/sdcc-user >
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