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FDS: implement CRC writing, reading, and checking

This commit is contained in:
goyuken 2012-10-27 01:04:54 +00:00
parent 5382a348dc
commit 452e1f0db4
1 changed files with 79 additions and 29 deletions
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108
BizHawk.Emulation/Consoles/Nintendo/NES/FDS/RamAdapter.cs
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@ -15,10 +15,16 @@ namespace BizHawk.Emulation.Consoles.Nintendo
{
for (int i = 0; i < pregap - 1; i++)
dest.WriteByte(0);
ushort crc = 0;
dest.WriteByte(0x80); // end of gap marker
dest.Write(data, 0, data.Length);
dest.WriteByte(0xff); // CRC (todo)
dest.WriteByte(0xff);
crc = CCITT_8(crc, 0x80);
for (int i = 0; i < data.Length; i++)
{
dest.WriteByte(data[i]);
crc = CCITT_8(crc, data[i]);
}
dest.WriteByte((byte)(crc & 0xff));
dest.WriteByte((byte)(crc >> 8));
}
static byte[] FixFDSSide(byte[] inputdisk)
@ -81,6 +87,25 @@ namespace BizHawk.Emulation.Consoles.Nintendo
return tmp;
}
static ushort CCITT(ushort crc, int bit)
{
int bitc = crc & 1;
crc >>= 1;
if ((bitc ^ bit) != 0)
crc ^= 0x8408;
return crc;
}
static ushort CCITT_8(ushort crc, byte b)
{
for (int i = 0; i < 8; i++)
{
int bit = (b >> i) & 1;
crc = CCITT(crc, bit);
}
return crc;
}
/// <summary>currently loaded disk side (ca 65k bytes)</summary>
byte[] disk = null;
@ -189,6 +214,7 @@ namespace BizHawk.Emulation.Consoles.Nintendo
{
bytetransferflag = false;
writereglatch = value;
//Console.WriteLine("!!4024:{0:x2}", value);
}
byte cached4025;
@ -198,6 +224,8 @@ namespace BizHawk.Emulation.Consoles.Nintendo
/// <summary>true if 4025.1 is set to true</summary>
bool transferreset = false;
ushort crc = 0;
// control reg
public void Write4025(byte value)
{
@ -223,6 +251,8 @@ namespace BizHawk.Emulation.Consoles.Nintendo
bytetransferflag = true;
// irq?
Console.WriteLine("FDS: Startwrite @{0} Reload {1:x2}", diskpos, writereglatch);
crc = 0;
writecomputecrc = true;
}
}
@ -230,6 +260,9 @@ namespace BizHawk.Emulation.Consoles.Nintendo
irq = false; // ??
cached4025 = value;
if ((cached4025 & 4) == 0)
if ((cached4025 & 0x10) != 0)
Console.WriteLine("FDS: Starting CRC");
}
// some bits come from outside RamAdapter
@ -238,7 +271,8 @@ namespace BizHawk.Emulation.Consoles.Nintendo
byte ret = 0;
if (bytetransferflag)
ret |= 0x02;
// bit 4 always 0: CRC not implemented
if (crc != 0)
ret |= 0x10;
if (diskpos == disksize)
ret |= 0x40; // end of disk
if (disk != null && !writeprotect)
@ -346,8 +380,10 @@ namespace BizHawk.Emulation.Consoles.Nintendo
bool lookingforendofgap = false;
/// <summary>number of CRC bytes read/written</summary>
//int numcrc;
/// <summary>
/// true if data being written to disk is currently being computed in CRC
/// </summary>
bool writecomputecrc; // this has to be latched because the "flush CRC" call comes in the middle of a byte, of course
void Read()
{
@ -363,6 +399,9 @@ namespace BizHawk.Emulation.Consoles.Nintendo
lookingforendofgap = false;//cached4025 &= unchecked((byte)~0x40); // stop looking for end of gap
readregpos = 0;
crc = 0;
// the first '1' is included in the CRC
crc = CCITT(crc, 1);
//bytetransferflag = true;
//if ((cached4025 & 0x80) != 0)
// irq = true;
@ -371,29 +410,27 @@ namespace BizHawk.Emulation.Consoles.Nintendo
}
else // reading actual data
{
crc = CCITT(crc, bit);
readreg &= (byte)~(1 << readregpos);
readreg |= (byte)(bit << readregpos);
readregpos++;
if (readregpos == 8)
{
readregpos = 0;
//if ((cached4025 & 0x10) == 0) // not in CRC
//{
bytetransferflag = true;
if ((cached4025 & 0x80) != 0)
irq = true;
lastreaddiskpos = diskpos;
Console.WriteLine("{0:x2} {1} @{2}", readreg, (cached4025 & 0x80) != 0 ? "RAISE" : " ", diskpos);
readreglatch = readreg;
//}
//else // when in CRC, don't send results back to user
//{
if ((cached4025 & 0x10) != 0)
{
Console.WriteLine("FDS: crc byte {0:x2} @{1}", readreg, diskpos);
cached4025 &= unchecked((byte)~0x10); // clear CRC reading
}
//}
bytetransferflag = true;
if ((cached4025 & 0x80) != 0)
irq = true;
lastreaddiskpos = diskpos;
//Console.WriteLine("{0:x2} {1} @{2}", readreg, (cached4025 & 0x80) != 0 ? "RAISE" : " ", diskpos);
readreglatch = readreg;
if ((cached4025 & 0x10) != 0)
{
Console.WriteLine("FDS: crc byte {0:x2} @{1}", readreg, diskpos);
cached4025 &= unchecked((byte)~0x10); // clear CRC reading. no real effect other than to silence debug??
Console.WriteLine("FDS: Final CRC {0:x4}", crc);
}
}
}
}
@ -417,6 +454,9 @@ namespace BizHawk.Emulation.Consoles.Nintendo
else
{
bittowrite = (writereg & (1 << writeregpos)) != 0;
//if ((cached4025 & 0x10) == 0)
if (writecomputecrc)
crc = CCITT(crc, bittowrite ? 1 : 0);
writeregpos++;
if (writeregpos == 8)
{
@ -427,15 +467,25 @@ namespace BizHawk.Emulation.Consoles.Nintendo
irq = true;
Console.WriteLine("FDS: Write @{0} Reload {1:x2}", diskpos + 1, writereglatch);
// it seems that after a successful CRC, the writereg is reset to 0 value. this is needed?
// TODO: actually write the CRC (2 bytes)
if ((cached4025 & 0x10) != 0)
{
Console.WriteLine("FDS: write clear CRC", readreg, diskpos);
cached4025 &= unchecked((byte)~0x10); // clear CRC reading
//writereg = 0; // don't do this
writereglatch = 0; //??
if (crc == 0)
{
cached4025 &= unchecked((byte)~0x10); // clear CRC reading
Console.WriteLine("FDS: write CRC commit finished");
// it seems that after a successful CRC, the writereglatch is reset to 0 value. this is needed?
writereglatch = 0;
}
Console.WriteLine("{0:x4}", crc);
writereg = (byte)crc;
Console.WriteLine("{0:x2}", writereg);
crc >>= 8;
Console.WriteLine("{0:x4}", crc);
// loaded the first CRC byte to write, so stop computing CRC on data
writecomputecrc = false;
}
}