Merge pull request #191 from ejona86/micropolis

Add Micropolis decoder

arch/micropolis/decoder.cc

@@ -0,0 +1,61 @@
+#include "globals.h"
+#include "fluxmap.h"
+#include "decoders/fluxmapreader.h"
+#include "decoders/decoders.h"
+#include "sector.h"
+#include "micropolis.h"
+#include "bytes.h"
+#include "fmt/format.h"
+
+/* The sector has a preamble of MFM 0x00s and uses 0xFF as a sync pattern. */
+static const FluxPattern SECTOR_SYNC_PATTERN(32, 0xaaaa5555);
+
+AbstractDecoder::RecordType MicropolisDecoder::advanceToNextRecord()
+{
+	_fmr->seekToIndexMark();
+	const FluxMatcher* matcher = nullptr;
+	_sector->clock = _fmr->seekToPattern(SECTOR_SYNC_PATTERN, matcher);
+	if (matcher == &SECTOR_SYNC_PATTERN) {
+		readRawBits(16);
+		return SECTOR_RECORD;
+	}
+	return UNKNOWN_RECORD;
+}
+
+/* Adds all bytes, with carry. */
+static uint8_t checksum(const Bytes& bytes) {
+	ByteReader br(bytes);
+	uint16_t sum = 0;
+	while (!br.eof()) {
+		if (sum > 0xFF) {
+			sum -= 0x100 - 1;
+		}
+		sum += br.read_8();
+	}
+	/* The last carry is ignored */
+	return sum & 0xFF;
+}
+
+void MicropolisDecoder::decodeSectorRecord()
+{
+	auto rawbits = readRawBits(MICROPOLIS_ENCODED_SECTOR_SIZE*16);
+	auto bytes = decodeFmMfm(rawbits).slice(0, MICROPOLIS_ENCODED_SECTOR_SIZE);
+	ByteReader br(bytes);
+
+	br.read_8();  /* sync */
+	_sector->logicalTrack = br.read_8();
+	_sector->logicalSide = _sector->physicalSide;
+	_sector->logicalSector = br.read_8();
+	if (_sector->logicalSector > 15)
+		return;
+	if (_sector->logicalTrack > 77)
+		return;
+
+	br.read(10);  /* OS data or padding */
+	_sector->data = br.read(256);
+	uint8_t wantChecksum = br.read_8();
+	uint8_t gotChecksum = checksum(bytes.slice(1, 2+266));
+	br.read(5);  /* 4 byte ECC and ECC-present flag */
+
+	_sector->status = (wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
+}

arch/micropolis/micropolis.h

@@ -0,0 +1,18 @@
+#ifndef ZILOGMCZ_H
+#define ZILOGMCZ_H
+
+#define MICROPOLIS_ENCODED_SECTOR_SIZE (1+2+266+6)
+
+class Sector;
+class Fluxmap;
+
+class MicropolisDecoder : public AbstractDecoder
+{
+public:
+	virtual ~MicropolisDecoder() {}
+
+	RecordType advanceToNextRecord();
+	void decodeSectorRecord();
+};
+
+#endif

doc/disk-micropolis.md

@@ -0,0 +1,49 @@
+Disk: Micropolis
+================
+
+Micropolis MetaFloppy disks use MFM and hard sectors. They were 100 TPI and
+stored 315k per side. Each of the 16 sectors contains 266 bytes of "user data,"
+allowing 10 bytes of metadata for use by the operating system. Micropolis DOS
+(MDOS) used the metadata bytes, but CP/M did not.
+
+Some later systems were Micropolis-compatible and so were also 100 TPI, like
+the Vector Graphic Dual-Mode Disk Controller which was paired with a Tandon
+drive.
+
+Reading disks
+-------------
+
+Just do:
+
+```
+fluxengine read micropolis
+```
+
+You should end up with a `micropolis.img` which is 630784 bytes long (for a
+normal DD disk). The image is written in CHS order, but HCS is generally used
+by CP/M tools so the image needs to be post-processed. For only half-full disks
+or single-sided disks, you can use `-s :s=0` to read only one side of the disk
+which works around the problem.
+
+The [CP/M BIOS](https://www.seasip.info/Cpm/bios.html) defined SELDSK, SETTRK,
+and SETSEC, but no function to select the head/side. This caused dual-sided
+floppies to be represented as twice the number of tracks with the second side's
+tracks logically following the first side (e.g., tracks 77-153). That produces
+results mostly indistinguishable from HCS.
+
+Useful references
+-----------------
+
+  - [Micropolis 1040/1050 S-100 Floppy Disk Subsystems User's Manual][micropolis1040/1050].
+    Section 6, pages 261-266. Documents pre-ECC sector format. Note that the
+    entire record, starting at the sync byte, is controlled by software
+
+  - [Vector Graphic Dual-Mode Disk Controller Board Engineering Documentation][vectordualmode].
+    Section 1.6.2. Documents ECC sector format
+
+  - [AltairZ80 Simulator Usage Manual][altairz80]. Section 10.6. Documents ECC
+    sector format and VGI file format
+
+[micropolis1040/1050]: http://www.bitsavers.org/pdf/micropolis/metafloppy/1084-01_1040_1050_Users_Manual_Apr79.pdf
+[vectordualmode]: http://bitsavers.org/pdf/vectorGraphic/hardware/7200-1200-02-1_Dual-Mode_Disk_Controller_Board_Engineering_Documentation_Feb81.pdf
+[altairz80]: http://www.bitsavers.org/simh.trailing-edge.com_201206/pdf/altairz80_doc.pdf

mkninja.sh

@@ -171,6 +171,7 @@ buildlibrary libbackend.a \
     arch/ibm/decoder.cc \
     arch/ibm/encoder.cc \
     arch/macintosh/decoder.cc \
+    arch/micropolis/decoder.cc \
     arch/mx/decoder.cc \
 	arch/tids990/decoder.cc \
 	arch/tids990/encoder.cc \
@@ -224,6 +225,7 @@ buildlibrary libfrontend.a \
     src/fe-readfb100.cc \
     src/fe-readibm.cc \
     src/fe-readmac.cc \
+    src/fe-readmicropolis.cc \
     src/fe-readmx.cc \
 	src/fe-readtids990.cc \
     src/fe-readvictor9k.cc \

src/fe-readmicropolis.cc

@@ -0,0 +1,26 @@
+#include "globals.h"
+#include "flags.h"
+#include "reader.h"
+#include "fluxmap.h"
+#include "encoders/encoders.h"
+#include "decoders/decoders.h"
+#include "sector.h"
+#include "sectorset.h"
+#include "record.h"
+#include "micropolis/micropolis.h"
+#include "fmt/format.h"
+
+static FlagGroup flags { &readerFlags };
+
+int mainReadMicropolis(int argc, const char* argv[])
+{
+	setReaderDefaultSource(":t=0-76");
+	setReaderDefaultOutput("micropolis.img");
+	setReaderRevolutions(21); /* 17 index holes * 1.25 */
+	flags.parseFlags(argc, argv);
+
+	MicropolisDecoder decoder;
+	readDiskCommand(decoder);
+	return 0;
+}
+

src/fluxengine.cc

@@ -21,6 +21,7 @@ extern command_cb mainReadF85;
 extern command_cb mainReadFB100;
 extern command_cb mainReadIBM;
 extern command_cb mainReadMac;
+extern command_cb mainReadMicropolis;
 extern command_cb mainReadMx;
 extern command_cb mainReadTiDs990;
 extern command_cb mainReadVictor9K;
@@ -78,6 +79,7 @@ static std::vector<Command> readables =
     { "fb100",         mainReadFB100,     "Reads FB100 disks.", },
     { "ibm",           mainReadIBM,       "Reads the ubiquitous IBM format disks.", },
     { "mac",           mainReadMac,       "Reads Apple Macintosh disks.", },
+    { "micropolis",    mainReadMicropolis, "Reads Micropolis disks.", },
     { "mx",            mainReadMx,        "Reads MX disks.", },
 	{ "tids990",       mainReadTiDs990,   "Reads Texas Instruments DS990 disks.", },
     { "victor9k",      mainReadVictor9K,  "Reads Victor 9000 disks.", },