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Micropolis: Add Vector ECC support

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This commit is contained in:
Eric Anderson
2023-02-25 11:23:12 -08:00
parent c623d95a80
commit 96d4df296d
6 changed files with 141 additions and 18 deletions
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81
arch/micropolis/decoder.cc
View File

@@ -59,6 +59,70 @@ uint8_t mzosChecksum(const Bytes& bytes)
return checksum;
}
static uint8_t b(uint32_t field, uint8_t pos)
{
return (field >> pos) & 1;
}
static uint8_t eccNextBit(uint32_t ecc, uint8_t data_bit)
{
// This is 0x81932080 which is 0x0104C981 with reversed bits
return b(ecc, 7) ^ b(ecc, 13) ^ b(ecc, 16) ^ b(ecc, 17) ^ b(ecc, 20)
^ b(ecc, 23) ^ b(ecc, 24) ^ b(ecc, 31) ^ data_bit;
}
uint32_t vectorGraphicEcc(const Bytes& bytes)
{
uint32_t e = 0;
Bytes payloadBytes = bytes.slice(0, bytes.size()-4);
ByteReader payload(payloadBytes);
while (!payload.eof()) {
uint8_t byte = payload.read_8();
for (int i = 0; i < 8; i++) {
e = (e << 1) | eccNextBit(e, byte >> 7);
byte <<= 1;
}
}
Bytes trailerBytes = bytes.slice(bytes.size()-4);
ByteReader trailer(trailerBytes);
uint32_t res = e;
while (!trailer.eof()) {
uint8_t byte = trailer.read_8();
for (int i = 0; i < 8; i++) {
res = (res << 1) | eccNextBit(e, byte >> 7);
e <<= 1;
byte <<= 1;
}
}
return res;
}
/* Fixes bytes when possible, returning true if changed. */
static bool vectorGraphicEccFix(Bytes& bytes, uint32_t syndrome)
{
uint32_t ecc = syndrome;
int pos = (MICROPOLIS_ENCODED_SECTOR_SIZE-5)*8+7;
bool aligned = false;
while ((ecc & 0xff000000) == 0) {
pos += 8;
ecc <<= 8;
}
for (; pos >= 0; pos--) {
bool bit = ecc & 1;
ecc >>= 1;
if (bit)
ecc ^= 0x808264c0;
if ((ecc & 0xff07ffff) == 0)
aligned = true;
if (aligned && pos % 8 == 0)
break;
}
if (pos < 0)
return false;
bytes[pos/8] ^= ecc >> 16;
return true;
}
class MicropolisDecoder : public Decoder
{
public:
@@ -132,6 +196,17 @@ public:
auto rawbits = readRawBits(MICROPOLIS_ENCODED_SECTOR_SIZE * 16);
auto bytes =
decodeFmMfm(rawbits).slice(0, MICROPOLIS_ENCODED_SECTOR_SIZE);
bool eccPresent = bytes[274] == 0xaa;
uint32_t ecc = 0;
if (_config.ecc_type() == MicropolisDecoderProto::VECTOR && eccPresent) {
ecc = vectorGraphicEcc(bytes.slice(0, 274));
if (ecc != 0) {
vectorGraphicEccFix(bytes, ecc);
ecc = vectorGraphicEcc(bytes.slice(0, 274));
}
}
ByteReader br(bytes);
int syncByte = br.read_8(); /* sync */
@@ -193,8 +268,10 @@ public:
_sector->data = bytes;
else
error("Sector output size may only be 256 or 275");
_sector->status =
(wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
if (wantChecksum == gotChecksum && (!eccPresent || ecc == 0))
_sector->status = Sector::OK;
else
_sector->status = Sector::BAD_CHECKSUM;
}
private:

16
arch/micropolis/encoder.cc
View File

@@ -8,7 +8,8 @@
static void write_sector(std::vector<bool>& bits,
unsigned& cursor,
const std::shared_ptr<const Sector>& sector)
const std::shared_ptr<const Sector>& sector,
MicropolisEncoderProto::EccType eccType)
{
if ((sector->data.size() != 256) &&
(sector->data.size() != MICROPOLIS_ENCODED_SECTOR_SIZE))
@@ -45,8 +46,15 @@ static void write_sector(std::vector<bool>& bits,
writer.write_8(0); /* Padding */
writer += sector->data;
writer.write_8(micropolisChecksum(sectorData.slice(1)));
for (int i = 0; i < 5; i++)
writer.write_8(0); /* 4 byte ECC and ECC not present flag */
uint8_t eccPresent = 0;
uint32_t ecc = 0;
if (eccType == MicropolisEncoderProto::VECTOR) {
eccPresent = 0xaa;
ecc = vectorGraphicEcc(sectorData + Bytes(4));
}
writer.write_be32(ecc);
writer.write_8(eccPresent);
}
for (uint8_t b : sectorData)
fullSector->push_back(b);
@@ -93,7 +101,7 @@ public:
for (const auto& sectorData : sectors) {
indexes.push_back(cursor);
prev_cursor = cursor;
write_sector(bits, cursor, sectorData);
write_sector(bits, cursor, sectorData, _config.ecc_type());
}
indexes.push_back(prev_cursor + (cursor - prev_cursor)/2);
indexes.push_back(cursor);

1
arch/micropolis/micropolis.h
View File

@@ -17,5 +17,6 @@ extern std::unique_ptr<Encoder> createMicropolisEncoder(
const EncoderProto& config);
extern uint8_t micropolisChecksum(const Bytes& bytes);
extern uint32_t vectorGraphicEcc(const Bytes& bytes);
#endif

13
arch/micropolis/micropolis.proto
View File

@@ -8,17 +8,30 @@ message MicropolisDecoderProto {
MICROPOLIS = 1;
MZOS = 2;
}
enum EccType {
NONE = 0;
VECTOR = 1;
}
optional int32 sector_output_size = 1 [default = 256,
(help) = "How much of the raw sector should be saved. Must be 256 or 275"];
optional ChecksumType checksum_type = 2 [default = AUTO,
(help) = "Checksum type to use: AUTO, MICROPOLIS, MZOS"];
optional EccType ecc_type = 3 [default = NONE,
(help) = "ECC type to use: NONE, VECTOR"];
}
message MicropolisEncoderProto {
enum EccType {
NONE = 0;
VECTOR = 1;
}
optional double clock_period_us = 1
[ default = 2.0, (help) = "clock rate on the real device" ];
optional double rotational_period_ms = 2
[ default = 200.0, (help) = "rotational period on the real device" ];
optional EccType ecc_type = 3 [default = NONE,
(help) = "ECC type to use for IMG data: NONE, VECTOR"];
}

24
doc/disk-micropolis.md
View File

@@ -22,13 +22,25 @@ pinout as a 96tpi PC 5.25" drive. In use they should be identical.
While most operating systems use the standard Micropolis checksum, Vector
Graphic MZOS uses a unique checksum. The decoder will automatically detect
the checksum type in use; however, a specific checksum type may be forced
using the `--decoder.micropolis.checksum_type=n` where the type is one of:
using the `--decoder.micropolis.checksum_type=TYPE` where TYPE is one of:
| Type | Description |
|------|-----------------------------------------|
| 0 | Automatically detect |
| 1 | Standard Micropolis (MDOS, CP/M, OASIS) |
| 2 | Vector Graphic MZOS |
| Checksum | Description |
|------------|-----------------------------------------|
| AUTO | Automatically detect |
| MICROPOLIS | Standard Micropolis (MDOS, CP/M, OASIS) |
| MZOS | Vector Graphic MZOS |
Later versions of the Micropolis format supported ECC, especially in
controllers with HDD support. The ECC can detect and correct errors. However,
it is unclear what ECC algorithm was used by each vendor. ECC is disabled by
default, but available for checking and correcting using
`--decoder.micropolis.ecc_type=TYPE` and for writing from IMG files using
`--encoder.micropolis.ecc_type=TYPE`, where TYPE is one of:
| ECC | Description |
|--------|------------------------------------------|
| NONE | No ECC processing enabled |
| VECTOR | Vector Graphic Dual-Mode Disk Controller |
The [CP/M BIOS](https://www.seasip.info/Cpm/bios.html) defined SELDSK, SETTRK,
and SETSEC, but no function to select the head/side. Double-sided floppies

24
src/formats/micropolis.textpb
View File

@@ -24,13 +24,25 @@ pinout as a 96tpi PC 5.25" drive. In use they should be identical.
While most operating systems use the standard Micropolis checksum, Vector
Graphic MZOS uses a unique checksum. The decoder will automatically detect
the checksum type in use; however, a specific checksum type may be forced
using the `--decoder.micropolis.checksum_type=n` where the type is one of:
using the `--decoder.micropolis.checksum_type=TYPE` where TYPE is one of:
| Type | Description |
|------|-----------------------------------------|
| 0 | Automatically detect |
| 1 | Standard Micropolis (MDOS, CP/M, OASIS) |
| 2 | Vector Graphic MZOS |
| Checksum | Description |
|------------|-----------------------------------------|
| AUTO | Automatically detect |
| MICROPOLIS | Standard Micropolis (MDOS, CP/M, OASIS) |
| MZOS | Vector Graphic MZOS |
Later versions of the Micropolis format supported ECC, especially in
controllers with HDD support. The ECC can detect and correct errors. However,
it is unclear what ECC algorithm was used by each vendor. ECC is disabled by
default, but available for checking and correcting using
`--decoder.micropolis.ecc_type=TYPE` and for writing from IMG files using
`--encoder.micropolis.ecc_type=TYPE`, where TYPE is one of:
| ECC | Description |
|--------|------------------------------------------|
| NONE | No ECC processing enabled |
| VECTOR | Vector Graphic Dual-Mode Disk Controller |
The [CP/M BIOS](https://www.seasip.info/Cpm/bios.html) defined SELDSK, SETTRK,
and SETSEC, but no function to select the head/side. Double-sided floppies