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The Apple II decoder is technically working now, but every disk I've tried is

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massively corrupt. Hmm.
This commit is contained in:
David Given
2019-02-28 23:09:19 +01:00
parent a3a680b426
commit 414c445bbe
3 changed files with 35 additions and 101 deletions
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125
lib/apple2/decoder.cc
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@@ -23,99 +23,40 @@ static int decode_data_gcr(uint8_t gcr)
};
/* This is extremely inspired by the MESS implementation, written by Nathan Woods
* and R. Belmont: https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap_dsk35.cpp
* and R. Belmont: https://github.com/mamedev/mame/blob/7914a6083a3b3a8c243ae6c3b8cb50b023f21e0e/src/lib/formats/ap2_dsk.cpp
*/
static std::vector<uint8_t> decode_crazy_data(const uint8_t* inp, int& status)
{
std::vector<uint8_t> output;
std::vector<uint8_t> output(APPLE2_SECTOR_LENGTH);
static const int LOOKUP_LEN = MAC_SECTOR_LENGTH / 3;
uint8_t b1[LOOKUP_LEN + 1];
uint8_t b2[LOOKUP_LEN + 1];
uint8_t b3[LOOKUP_LEN + 1];
for (int i=0; i<=LOOKUP_LEN; i++)
uint8_t checksum = 0;
for (unsigned i = 0; i < APPLE2_ENCODED_SECTOR_LENGTH; i++)
{
uint8_t w4 = *inp++;
uint8_t w1 = *inp++;
uint8_t w2 = *inp++;
uint8_t w3 = (i != 174) ? *inp++ : 0;
uint8_t b = decode_data_gcr(*inp++);
uint8_t newvalue = b ^ checksum;
b1[i] = (w1 & 0x3F) | ((w4 << 2) & 0xC0);
b2[i] = (w2 & 0x3F) | ((w4 << 4) & 0xC0);
b3[i] = (w3 & 0x3F) | ((w4 << 6) & 0xC0);
if (i >= 0x56)
{
/* 6 bit */
output[i - 0x56] |= (newvalue << 2);
}
else
{
/* 3 * 2 bit */
output[i + 0x00] = ((newvalue >> 1) & 0x01) | ((newvalue << 1) & 0x02);
output[i + 0x56] = ((newvalue >> 3) & 0x01) | ((newvalue >> 1) & 0x02);
if ((i + 0xAC) < APPLE2_SECTOR_LENGTH)
output[i + 0xAC] = ((newvalue >> 5) & 0x01) | ((newvalue >> 3) & 0x02);
}
checksum = newvalue;
}
/* Copy from the user's buffer to our buffer, while computing
* the three-byte data checksum. */
uint32_t c1 = 0;
uint32_t c2 = 0;
uint32_t c3 = 0;
unsigned count = 0;
for (;;)
{
c1 = (c1 & 0xFF) << 1;
if (c1 & 0x0100)
c1++;
uint8_t val = b1[count] ^ c1;
c3 += val;
if (c1 & 0x0100)
{
c3++;
c1 &= 0xFF;
}
output.push_back(val);
val = b2[count] ^ c3;
c2 += val;
if (c3 > 0xFF)
{
c2++;
c3 &= 0xFF;
}
output.push_back(val);
if (output.size() == 524)
break;
val = b3[count] ^ c2;
c1 += val;
if (c2 > 0xFF)
{
c1++;
c2 &= 0xFF;
}
output.push_back(val);
count++;
}
uint8_t c4 = ((c1 & 0xC0) >> 6) | ((c2 & 0xC0) >> 4) | ((c3 & 0xC0) >> 2);
c1 &= 0x3f;
c2 &= 0x3f;
c3 &= 0x3f;
c4 &= 0x3f;
uint8_t g4 = *inp++;
uint8_t g3 = *inp++;
uint8_t g2 = *inp++;
uint8_t g1 = *inp++;
if ((g4 == c4) && (g3 == c3) && (g2 == c2) && (g1 == c1))
status = Sector::OK;
checksum &= 0x3f;
uint8_t wantedchecksum = decode_data_gcr(*inp);
status = (checksum == wantedchecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
return output;
}
uint8_t decode_side(uint8_t side)
{
/* Mac disks, being weird, use the side byte to encode both the side (in
* bit 5) and also whether we're above track 0x3f (in bit 6).
*/
return !!(side & 0x40);
}
uint8_t combine(uint16_t word)
{
return word & (word >> 7);
@@ -140,7 +81,7 @@ SectorVector Apple2Decoder::decodeToSectors(
uint32_t signature = read_be24(&rawbytes[0]);
switch (signature)
{
case MAC_SECTOR_RECORD:
case APPLE2_SECTOR_RECORD:
{
uint8_t volume = combine(read_be16(&rawbytes[3]));
nextTrack = combine(read_be16(&rawbytes[5]));
@@ -150,24 +91,16 @@ SectorVector Apple2Decoder::decodeToSectors(
break;
}
case MAC_DATA_RECORD:
case APPLE2_DATA_RECORD:
{
if (!headerIsValid)
break;
headerIsValid = false;
uint8_t inputbuffer[MAC_SECTOR_LENGTH * 8/6 + 5] = {};
for (unsigned i=0; i<sizeof(inputbuffer); i++)
{
auto p = rawbytes.begin() + 4 + i;
if (p > rawbytes.end())
break;
inputbuffer[i] = decode_data_gcr(*p);
}
std::vector<uint8_t> clippedbytes(rawbytes);
clippedbytes.resize(APPLE2_ENCODED_SECTOR_LENGTH + 5);
int status = Sector::BAD_CHECKSUM;
auto data = decode_crazy_data(inputbuffer, status);
auto data = decode_crazy_data(&clippedbytes[4], status);
auto sector = std::unique_ptr<Sector>(
new Sector(status, nextTrack, 0, nextSector, data));
@@ -183,7 +116,7 @@ SectorVector Apple2Decoder::decodeToSectors(
int Apple2Decoder::recordMatcher(uint64_t fifo) const
{
uint32_t masked = fifo & 0xffffff;
if ((masked == MAC_SECTOR_RECORD) || (masked == MAC_DATA_RECORD))
if ((masked == APPLE2_SECTOR_RECORD) || (masked == APPLE2_DATA_RECORD))
return 24;
return 0;
}