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Skip copying melondDS default MAC address #4648

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cc886d2
Skip copying melondDS default MAC address
Real96 Mar 2, 2026
c865994
Check if external firmware MAC address is valid
Real96 Mar 2, 2026
7efe60e
Rebuild melonDS
Real96 Mar 3, 2026
3b4c71c
update melondDS MAC address validation
Real96 Apr 5, 2026
1a6bc52
update comments
Real96 Apr 6, 2026
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Binary file modified Assets/dll/melonDS.wbx.zst
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23 changes: 22 additions & 1 deletion waterbox/melon/BizConsoleCreator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,17 @@ static std::unique_ptr<T> CreateBiosImage(u8* biosData, u32 biosLength, std::opt
return std::move(bios);
}

static bool isValidMacAddress(const melonDS::MacAddress& mac)
{
// 48bit MAC address v1–v5: 00:09:BF:XX:XX:XX
const bool isV1toV5 = mac[0] == 0x00 && mac[1] == 0x09 && mac[2] == 0xBF;

// 48bit MAC address v6–v7: 00:16:56:XX:XX:XX
const bool isV6toV7 = mac[0] == 0x00 && mac[1] == 0x16 && mac[2] == 0x56;
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@CasualPokePlayer CasualPokePlayer Mar 16, 2026

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These checks appear to be non-exhastive.

For DSi, A4 C0 E1 is valid.
For DS Lite, 00 25 A0 is valid.
For iQue DS Lite, 00 1D BC is valid.

In theory, there's potentially a ton of other valid MAC addresses, as Nintendo has registered a ton of MAC prefixes. It might be better to just make sure it's not all 0xFFs (not uncommon to find with "no-intro" matching dumps which 0xFF wifi area) along with not being 03:09:BF (broadcast channel, not valid)

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@Real96 Real96 Apr 6, 2026

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Done


return isV1toV5 || isV6toV7;
}

static void SanitizeExternalFirmware(melonDS::Firmware& firmware)
{
auto& header = firmware.GetHeader();
Expand All @@ -84,7 +95,17 @@ static void SanitizeExternalFirmware(melonDS::Firmware& firmware)
memset(&header.Bytes[0x28], 0xFF, 2);
}

memcpy(&header.Bytes[0x2C], &defaultHeader.Bytes[0x2C], 0x136);
memcpy(&header.Bytes[0x2C], &defaultHeader.Bytes[0x2C], 10);

// MAC address offset is 0x36, so we skip writing from 0x36 to 0x3B (48 bit)
// to avoid copying melonDS default MAC address 0x0009BF112233
// only if the external firmware MAC address is valid
if (!isValidMacAddress(header.MacAddr))
{
memcpy(&header.Bytes[0x36], &defaultHeader.Bytes[0x36], 6);
}

memcpy(&header.Bytes[0x3C], &defaultHeader.Bytes[0x3C], 0x126);
memset(&header.Bytes[0x162], 0xFF, 0x9E);

if (isDSiFw)
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