feat: list the six BizHawk DSi NAND slots

FirmwareDatabase.cs:405-410 declares NDS+NAND_JPN, EUR, USA, AUS, CHN
and KOR, each with a placeholder hash and 251658240 + 64 bytes. In DSi
mode DecideNAND takes the first one set, limited to the regions a
DSi-enhanced header allows, and stops the load with none
(MelonDS.cs:114, 304, 484, 684-706). DSi mode is off by default, so the
entries are optional, like DSi_Firmware.bin and the DSi BIOS slots.

emulators/bizhawk.yml

@@ -79,10 +79,14 @@ notes: |
   firmware folder by hash, and a user specification can name any file.
   Unacceptable and Bad options, and slots with a placeholder hash, are
   reached only through a user specification. The six DSi NAND slots
-  (NDS+NAND_JPN, EUR, USA, AUS, CHN, KOR) are of that kind and are not
-  listed.
+  (NDS+NAND_JPN, EUR, USA, AUS, CHN, KOR) are of that kind. In DSi mode
+  (the UseDSi setting, or DSiWare content) the core takes the first of
+  them that is set, in the order JPN, USA, EUR, AUS, CHN, KOR, and for a
+  DSi-enhanced title only the regions its header flags allow. With none it
+  stops the load.
   ref: src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:35-71,
-       src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:405-410
+       src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:405-410,
+       src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:114, 304, 684-706
 
   required follows what the core does on a default configuration for that
   system's content. GetFirmwareOrThrow stops the load, GetFirmware lets the
@@ -144,6 +148,60 @@ files:
     source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:402, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:469"
     note: "Slot NDS+firmwarei has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode with real BIOS files."
 
+  - name: "DSi_Nand_JPN.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (Japan)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:405, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_JPN has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
+  - name: "DSi_Nand_EUR.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (Europe)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:406, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_EUR has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
+  - name: "DSi_Nand_USA.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (USA)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:407, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_USA has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
+  - name: "DSi_Nand_AUS.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (Australia)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:408, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_AUS has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
+  - name: "DSi_Nand_CHN.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (China)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:409, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_CHN has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
+  - name: "DSi_Nand_KOR.bin"
+    system: nintendo-ds
+    required: false
+    size: 251658304
+    storage: large_file
+    description: "DSi NAND (Korea)"
+    source_ref: "src/BizHawk.Emulation.Common/Database/FirmwareDatabase.cs:410, src/BizHawk.Emulation.Cores/Consoles/Nintendo/NDS/MelonDS.cs:484, 684-706"
+    note: "Slot NDS+NAND_KOR has a placeholder hash, so the scan never finds it. Only a user specification reaches it. Read in DSi mode. The size includes the 64-byte nocash footer."
+
   - name: "32X_G_BIOS.BIN"
     system: sega-32x
     required: false

tests/test_audit_regressions.py

@@ -6165,5 +6165,25 @@ class AmigaCdDriversLiveInTheExtendedRom(unittest.TestCase):
                 self.assertNotIn("hle_fallback", entries[name])
 
 
+class BizHawkListsEveryDsiNandSlot(unittest.TestCase):
+    """FirmwareDatabase.cs:405-410 declares six DSi NAND slots, each a
+    placeholder hash and 251658240 + 64 bytes, and DecideNAND
+    (MelonDS.cs:684-706) stops a DSi load when none is set. The profile
+    listed DSi_Firmware.bin, a placeholder slot of the same kind, and left
+    the NANDs out."""
+
+    def test_the_six_regional_nands_are_declared(self):
+        profile = yaml.safe_load(
+            (ROOT / "emulators" / "bizhawk.yml").read_text(encoding="utf-8")
+        )
+        entries = {f["name"]: f for f in profile["files"]}
+        for region_code in ("JPN", "EUR", "USA", "AUS", "CHN", "KOR"):
+            with self.subTest(region=region_code):
+                entry = entries[f"DSi_Nand_{region_code}.bin"]
+                self.assertEqual(entry["size"], 251658240 + 64)
+                self.assertIs(entry["required"], False)
+                self.assertNotIn("sha1", entry)
+
+
 if __name__ == "__main__":
     unittest.main()