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Trayoff and earliest running of code.

Mr_Da_Greatest - Nov 25, 2024

		Mr_Da_Greatest		Nov 25, 2024
			In the sgl 1.0 documentation there is a snippet of code about being able to open the tray without turning on the multiplayer. The code has been modified to not rts but branch afterwards. It also disables and enables interrupts. Its SH2 assembly .S so needs to be compiled. mov #-16,r0 ! Disable interrupts extu.b r0,r0 ldc r0,sr nop mov.l @(010,PC),r4 ! Load GDB to 60ffc00 which was SGL1 stack pointer nop ldc r4,gbr bra Trayoff .long 0x060ffc00 Trayoff: tst r4,r4 movt r0 mov.l @(020,PC),r2 ! 0x25890008 , changed to 020 for PC offset mov #0,r1 mov.b r0,@(180,gbr) mov.w r1,@r2 ! removed rts since no longer a function, set 0 to CD_Status nop bra Enable_itr ! bra added labels nop nop and r8,r5 ! The last 2 is not code but 0x25890008 address for the mov @(020, PC), r2 clrt Enable_itr: ! Enable interrupts mov #0,r0 ldc r0,sr I have been able to add this to a modified IP.BIN file. It works on Mednafen, Yabause, and with Pseudosaturn on real hardware. With Pseudosaturn I can load a file open the tray and it will not go to multiplayer. I can put in another CD since the first file is currently just TEST.BIN (pharaoh head), close and no problem. In the future if a loader is made for first CD it might be a way to load another CD. The problem is on real hardware this code runs after the 4th security check (TOC). 1) SEGA SEGASATURN at start of IP BIN 2) SEC1.BIN file (from Psy-Q) 3) SEC2.BIN file (from Psy-Q) 4) TOC check Other than cartridge space 0x2200000, is there any other way to run code before TOC? Could Audio/Mode2 or other weird mixed mode CD's work? On a side note this Photo-operator CD does the same thing where after loading you can freely open the CD tray without invoking multiplayer. Currently working on changing SEC2.BIN file for the last branch to jump back to 0x70 in IP.BIN (game name), which gives 0x70-DF space for code (potentially). Thanks for your assistance.

		vbt		Nov 27, 2024
			Mr_Da_Greatest said: would it mean you could also convert a game not compatible with fld lib to a multiboot game ?

		Mr_Da_Greatest		Nov 27, 2024
			@vbt... I am not sure. In my hands I have not gotten fld.lib (fld_knl.bin) to work. I am still looking through old DEVTOOLS.PDF I have seen it in Sega Sampler and Rockin'B Atlas creator. That whole fld.lib and associate files has always been of interest since to me since it has an internal TOC check and Cdblock unlock. Again I would need to figure out how to run it before system TOC. I think I might have found the SEC1.BIN check in the bio100jp.asm (L001B04) which is (1B50 in Yabause). It says it checks the first 0x340 bytes but when I change byte 341 it still goes to multiplayer. So still some work to do there. if there was a way to change 1 assembly code in the bios (001B04 D205 to D206) then instead of checking 0x6200 (bios copy of SEC1) it would check 0x06002100 (IP.BIN) version against itself. 0x6200 itself I believe is loaded from boot_app.asm. That could potentially let you run modified SEC1.bin files before TOC checking.