Will Deacon <will.dea...@arm.com> writes: > Hi Al, Matt, > > On Mon, May 06, 2013 at 09:53:30PM +0100, Al Viro wrote: >> On Mon, May 06, 2013 at 01:19:51PM -0700, Matt Turner wrote: >> >> > I'm not sure of the interpretation that LDA counts as a memory access. >> > >> > The manual says it's Ra <- Rbv + SEXT(disp). >> > >> > It's not touching memory that I can see. >> >> More to the point, the same manual gives explicit list of instructions >> that shouldn't occur between LDx_L and STx_C, and LDA does not belong to any >> of those. I suspect that Will has misparsed the notations in there - LDx is >> present in the list, but it's _not_ "all instructions with mnemonics starting >> with LD", just the 4 "load integer from memory" ones. FWIW, instructions >> with that encoding (x01xxx<a:5><b:5><offs:16>) are grouped so: >> LDAx - LDA, LDAH; load address >> LDx - LDL, LDQ, LDBU, LDWU; load memory data into integer register >> LDQ_U; load unaligned >> LDx_L - LDL_L, LDQ_L; load locked >> STx_C - STL_C, STQ_C; store conditional >> STx - STL, STQ, STB, STW; store >> STQ_U; store unaligned > > Your suspicions are right! I did assume that LDA fell under the LDx class, > so apologies for the false alarm. I suspect I should try and get out more, > rather than ponder over this reference manual.
LDA uses the address generation circuitry from the load/store unit, but it does not actually access memory. It is merely a convenient way of performing certain arithmetic operations, be it for scheduling reasons or for the different range of immediate values available. -- Måns Rullgård m...@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
