Yes... this would work for single byte op codes and some stack related operations but not for some indexed operations where such a memory access (it's actually not only dummy reads but also some dummy writes) happens if there's a page boundary crossing. I'd like to transparently manipulate the memory- of course omitting I/O area where interrupt flags and such stuff gets cleared when there's an access. On 13.10.23 13:40, groepaz_at_gmx.net wrote: > Am Freitag, 13. Oktober 2023, 13:30:16 CEST schrieb Frank Wolf: >> Hi! >> >> As many here know the 6502 actually fetches and discards the next opcode >> when executing >> >> single byte instruction before actually fetching the OP code again and >> it also write back actual >> >> data before writing the real data to a specific memory address; the so >> called "dummy reads". >> >> Is there any easy way to detect or predict a dummy read? Maybe when >> looking at some internal signals >> >> (e.g. Visual6502) without reimplementing the full instruction decoder? > I'd just make a table with 256 entries, and in each entry use the bits to > indicate those dummy cycles. That makes "is this a dummy cycle" a simple > lookup based on current instruction and current cycle. > > What are you trying to do? :) > > -- > > http://hitmen.eu http://ar.pokefinder.org > http://vice-emu.sourceforge.net http://magicdisk.untergrund.net > > Adults are obsolete children > > > > > >Received on 2023-10-13 14:00:30
Archive generated by hypermail 2.3.0.