Cheat Search Memory Space Limited to 256KB; Missing On-chip Work RAM?

[Hzbeta]

In issue #293, I learned that the current mGBA core might have a bug causing its search space to be only from 0x00000000 to 0x00007FFF. I have the same problem on my end, but it was also mentioned that after switching to the vba-m core, the search space expanded to 0x0003FFFF.

However, I want to know whether having a maximum cheat search memory space of 0x0003FFFF is normal for GBA games. I found that the GBA memory map is as follows:

General Internal Memory
  00000000-00003FFF   BIOS - System ROM         (16 KBytes)
  00004000-01FFFFFF   Not used
  02000000-0203FFFF   WRAM - On-board Work RAM  (256 KBytes) 2 Wait
  02040000-02FFFFFF   Not used
  03000000-03007FFF   WRAM - On-chip Work RAM   (32 KBytes)
  03008000-03FFFFFF   Not used
  04000000-040003FE   I/O Registers
  04000400-04FFFFFF   Not used
Internal Display Memory
  05000000-050003FF   BG/OBJ Palette RAM        (1 Kbyte)
  05000400-05FFFFFF   Not used
  06000000-06017FFF   VRAM - Video RAM          (96 KBytes)
  06018000-06FFFFFF   Not used
  07000000-070003FF   OAM - OBJ Attributes      (1 Kbyte)
  07000400-07FFFFFF   Not used
External Memory (Game Pak)
  08000000-09FFFFFF   Game Pak ROM/FlashROM (max 32MB) - Wait State 0
  0A000000-0BFFFFFF   Game Pak ROM/FlashROM (max 32MB) - Wait State 1
  0C000000-0DFFFFFF   Game Pak ROM/FlashROM (max 32MB) - Wait State 2
  0E000000-0E00FFFF   Game Pak SRAM    (max 64 KBytes) - 8bit Bus width
  0E010000-0FFFFFFF   Not used
Unused Memory Area
  10000000-FFFFFFFF   Not used (upper 4bits of address bus unused)

I tested "Metroid Zero Mission" and "Metroid Fusion", and within the 0x0003FFFF memory space, I could not find the player HP; it seems they are stored in memory beyond this range. From 0x00000000 to 0x0003FFFF is only 256KB. I am not sure how this memory space is mapped in the GBA, but it seems that it cannot include both the On-board Work RAM (256KB) and the On-chip Work RAM (32KB), because together they require 288KB. In the standalone version of mGBA, I can correctly locate the HP at an address within the On-chip Work RAM region, which seems to indicate that the On-chip Work RAM is not included in the current search space supported by RetroArch (256KB).

I am not sure whether this is a bug or an intentional feature. If it is a bug, I hope it can be fixed. If it is intentional, I hope the memory space can be increased to 288KB, so that it can completely include both the On-board Work RAM and the On-chip Work RAM. Because the cheat functions provided by the emulator core are limited, only allowing setting fixed values and cannot perform logical judgments and other operations, and currently the "make controller rumble" feature provided by RetroArch cannot be set to functions such as rumbling when taking damage because the search space does not include the HP address.

Thank you for your attention to this issue. I look forward to your feedback and any potential fixes or enhancements. If needed, I would be happy to provide any assistance I can.