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Fixed a DSK write checksum bug

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--HG--
extra : convert_revision : svn%3Affd33b8c-2492-42e0-bdc5-587b920b7d6d/trunk%4024004
This commit is contained in:
Nick Westgate 2009-07-15 16:05:53 +00:00
parent e95423c606
commit 7c2048f0c3
1 changed files with 19 additions and 7 deletions
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26
Virtu/DiskDsk.cs
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@ -84,7 +84,7 @@ public override void WriteTrack(int number, int fraction, byte[] buffer)
if (!Read3Nibbles(0xD5, 0xAA, 0xAD, 0x20))
break; // no data prologue
if (ReadDataNibbles((track * SectorCount + DosOrderToLogicalSector[sector]) * SectorSize) != 0)
if (!ReadDataNibbles((track * SectorCount + DosOrderToLogicalSector[sector]) * SectorSize))
break; // bad data checksum
if ((ReadNibble() != 0xDE) || (ReadNibble() != 0xAA))
@ -94,7 +94,7 @@ public override void WriteTrack(int number, int fraction, byte[] buffer)
}
if (sectorsDone != 0xFFFF)
throw new Exception("disk error"); // TODO: not sure what we want here
throw new Exception("disk error"); // TODO: we should alert the user and "dump" a NIB
}
private byte ReadNibble()
@ -133,7 +133,19 @@ private int ReadNibble44()
return (((ReadNibble() << 1) | 0x1) & ReadNibble());
}
private byte ReadDataNibbles(int sectorOffset)
private byte ReadTranslatedNibble()
{
byte data = NibbleToByte[ReadNibble()];
// TODO: check that invalid nibbles aren't used
// (put 0xFFs for invalid nibbles in the table)
//if (data == 0xFF)
//{
//throw an exception
//}
return data;
}
private bool ReadDataNibbles(int sectorOffset)
{
byte a, x, y;
@ -141,17 +153,17 @@ private byte ReadDataNibbles(int sectorOffset)
a = 0;
do // fill and de-nibblize secondary buffer
{
a = _secondaryBuffer[--y] = (byte)(a ^ NibbleToByte[ReadNibble()]);
a = _secondaryBuffer[--y] = (byte)(a ^ ReadTranslatedNibble());
}
while (y > 0);
do // fill and de-nibblize secondary buffer
{
a = _primaryBuffer[y++] = (byte)(a ^ NibbleToByte[ReadNibble()]);
a = _primaryBuffer[y++] = (byte)(a ^ ReadTranslatedNibble());
}
while (y != 0);
byte checksum = NibbleToByte[ReadNibble()]; // should be 0
int checksum = a ^ ReadTranslatedNibble(); // should be 0
x = y = 0;
do // decode data
@ -166,7 +178,7 @@ private byte ReadDataNibbles(int sectorOffset)
}
while (++y != 0);
return checksum;
return (checksum == 0);
}
private void WriteNibble(int data)