Hi Yujiecui, The fetch stage in O3CPU fetches cache lines from instruction cache and also calls ISA specific decoder implementation to decode the raw bytes into instructions and access the corresponding micro-ops for these instructions (In other words, fetch stage outputs the micrco-ops). That's why you are seeing all these decode calls. As far as I understand (specifically for x86), the functions you are referring to will decode a machine instruction corresponding to the given PC, check if the instruction exist across the cache block boundary and fetch more bytes (i.e. next cache block) etc. As far as Rom is concerned, I think it holds the micro-ops.
I will suggest you have a look at the following page: http://www.m5sim.org/X86_Instruction_decoding and decoder implementation for some ISA e.g. src/arch/x86/decoder.hh -Ayaz On Tue, Nov 3, 2020 at 4:52 AM yujiecui--- via gem5-users < gem5-users@gem5.org> wrote: > In the fetch function in the src/cpu/O3/fetch.impl file, when fetching > instructions to the fetch queue, I saw some operations on the decoder, > which made me very confused. For example, decoder[tid]->decode(thisPC), > decoder[tid]->instReady(), decoder[tid]->needMoreBytes(), > decoder[tid]->moreBytes(thisPC, fetchAddr, inst). Why are there so many > decoding operations when fetching instructions into the fetch queue? What > is the role of decoder[tid] here? What does needMoreBytes() do? > > Still fetch function in the src/cpu/O3/fetch.impl file, I saw some > RomMicroPC. I want to know what kind of instructions are in rom? > > I stepped through it many times, but I still have trouble understanding. > All related answers are very welcome. Thanks > _______________________________________________ > gem5-users mailing list -- gem5-users@gem5.org > To unsubscribe send an email to gem5-users-le...@gem5.org > %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s >
_______________________________________________ gem5-users mailing list -- gem5-users@gem5.org To unsubscribe send an email to gem5-users-le...@gem5.org %(web_page_url)slistinfo%(cgiext)s/%(_internal_name)s
