some code for the madison z-ram ? On 27/08/2020 14:02, groepaz_at_gmx.net wrote: > Am Donnerstag, 27. August 2020, 13:53:43 CEST schrieb Hans Liss: >> On 2020-08-27 13:44, groepaz_at_gmx.net wrote: >>> Am Donnerstag, 27. August 2020, 13:41:46 CEST schrieb groepaz_at_gmx.net: >>>> Am Donnerstag, 27. August 2020, 13:32:56 CEST schrieb Hans Liss: >>>>> Odd code. It seems to have some magic I/O at $8000/$8001, with $8001 >>>>> maybe producing side effects on read. >>>>> >>>>> Also, the sequence starting at $e7a0 is kinda epic. It laboriously >>>>> stores code, instruction by instruction, at $0400 - $041b, and then >>>>> jumps to $0400. I wonder why. >>>> that would be the typical thing to do if you eg want to bank out the ROM >>>> you are running from, to call code from another ROM (bank), or from RAM >>>> >>>> $400x seems to be I/O to me as well... there really must be more to this, >>>> ie without the schematics or knowledge of the hardware it doesnt make a >>>> lot of sense >>> this is the code at 0400 >>> >>> .C:0400 A2 FF LDX #$FF >>> .C:0402 A0 FF LDY #$FF >>> .C:0404 A9 5C LDA #$5C >>> .C:0406 8D 00 80 STA $8000 >>> .C:0409 CA DEX >>> .C:040a D0 F8 BNE $0404 >>> .C:040c 88 DEY >>> .C:040d D0 F5 BNE $0404 >>> .C:040f A9 A2 LDA #$A2 >>> .C:0411 CD 00 04 CMP $0400 >>> .C:0414 D0 03 BNE $0419 >>> .C:0416 4C 32 E8 JMP $E832 >>> .C:0419 4C 2D E8 JMP $E82D >> You were faster! :) >> >> It's a bit strange. It's a clear sign of self-modifying code, checking >> the value at $0400 like that. But I can't see anything in the ROM code >> that might change that value. > perhaps there were two CPUs in the system? and this is the "locking" between > them? that kind of thing wasnt terribly uncommon in the PETs > > -- > > http://hitmen.eu http://ar.pokefinder.org > http://vice-emu.sourceforge.net http://magicdisk.untergrund.net > > Choose any two: 1) Enjoy your job. 2) Work within the law. 3) Make lots of > money. > > > > >Received on 2020-08-27 15:01:18
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