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Fix parsing of PRG-/CHR-ROM size from NES 2.0 headers (NesHawk)

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YoshiRulz 2025-04-08 12:24:54 +10:00
parent 41ad4ff6e9
commit 60fdcb3f72
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1 changed files with 13 additions and 5 deletions
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18
src/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/NES.iNES.cs
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@ -23,15 +23,23 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
if ((data[7] & 0x0c) == 0x08)
{
// process as iNES v2
static int ReadEMFormAreaSize(int msn, int lsb, int nonEMFormBlockSizeKiB)
{
if (msn is not 0xF) return ((msn << 8) | lsb) * nonEMFormBlockSizeKiB;
// else exponent-multiplier form: `2^E * (2*M + 1)` bytes, where M is the least significant 2 bits, and E is the next 6 bits
var prgSize = (2 * (lsb & 0xFC) + 1) << (1 + (lsb & 0x03));
// convert to KiB, rounding up
var frac = prgSize & 0x3FF;
prgSize >>= 10;
return frac is 0 ? prgSize : prgSize + 1;
}
CartV2 = new CartInfo
{
PrgSize = data[4] | data[9] << 8 & 0xf00,
ChrSize = data[5] | data[9] << 4 & 0xf00
PrgSize = ReadEMFormAreaSize(msn: data[9] & 0x0F, lsb: data[4], nonEMFormBlockSizeKiB: 16),
ChrSize = ReadEMFormAreaSize(msn: data[9] >> 4, lsb: data[5], nonEMFormBlockSizeKiB: 8),
};
CartV2.PrgSize *= 16;
CartV2.ChrSize *= 8;
CartV2.WramBattery = (data[6] & 2) != 0; // should this be respected in v2 mode??
int wrambat = iNES2Wram(data[10] >> 4);