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Merge pull request #27 from davidgiven/apple2
Add basic Apple 2 support.
This commit is contained in:
David Given
GitHub
58
doc/apple2.md
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58
doc/apple2.md
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Apple II disks
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==============
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Apple II disks are nominally fairly sensible 40-track, single-sided, 256
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bytes-per-sector jobs. However, they come in two varieties: DOS 3.3 and
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above, and pre-DOS 3.3. They use different GCR encoding systems, dubbed
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6-and-2 and 5-and-3, and are mutually incompatible (although in some rare
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cases you can mix 6-and-2 and 5-and-3 sectors on the same disk).
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The difference is in the drive controller; the 6-and-2 controller is capable
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of a more efficient encoding, and can fit 16 sectors on a track, storing
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140kB on a disk. The 5-and-3 controller can only fit 13, with a mere 114kB.
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Both formats use GCR (in different varieties) in a nice, simple grid of
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sectors, unlike the Macintosh. Like the Macintosh, there's a crazy encoding
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scheme applied to the data before it goes down on disk to speed up
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checksumming.
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Macintosh disks come in two varieties: the newer 1440kB ones, which are
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perfectly ordinary PC disks you should use `fe-readibm` to read, and the
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older 800kB disks (and 400kB for the single sides ones). They have 80 tracks
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and up to 12 sectors per track.
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In addition, a lot of the behaviour of the drive was handled in software.
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This means that Apple II disks can do all kinds of weird things, including
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having spiral tracks! Copy protection for the Apple II was even madder than
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on other systems.
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FluxEngine can only read well-behaved, DOS 3.3 6-and-2 disks. It doesn't even
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try to handle the weird stuff.
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Sadly, DOS 3.3 also applies logical sector remapping on top of the physical
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sector numbering on the disk, and this _varies_ depending on what the disk is
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for. FluxEngine doesn't attempt to remap sectors, instead giving you an exact
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copy of what's on the disk, so you may need to do some work before the images
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are usable in emulators.
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Reading discs
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-------------
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Just do:
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```
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.obj/fe-readapple2
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```
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You should end up with an `apple2.img` which is 143360 bytes long.
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**Big warning!** The image may not work in an emulator, due to the
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logical sector mapping issue described above.
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Useful references
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-----------------
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- [Beneath Apple DOS](https://fabiensanglard.net/fd_proxy/prince_of_persia/Beneath%20Apple%20DOS.pdf)
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- [MAME's ap2_dsk.cpp file](https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap2_dsk.cpp)
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@@ -85,6 +85,7 @@ Here's the table.
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| [Acorn ADFS](acornadfs.html) | 🦖 | | single- and double- sided |
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| [Acorn DFS](acorndfs.html) | 🦄 | | |
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| [Ampro Little Board](ampro.html) | 🦖 | | |
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| [Apple II DOS 3.3](apple2.html) | 🦖 | | doesn't do logical sector remapping |
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| [Commodore Amiga](amiga.html) | 🦖 | | |
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| [Commodore 64 1541](c64.html) | 🦖 | | and probably the other GCR formats |
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| [Brother 120kB](brother.html) | 🦄 | | |
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@@ -53,8 +53,7 @@ touch](https://github.com/davidgiven/fluxengine/issues/new).
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Useful references
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-----------------
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- [MAME's ap_dsk35.cpp file]
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(https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap_dsk35.cpp),
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- [MAME's ap_dsk35.cpp file](https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap_dsk35.cpp),
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without which I'd never have managed to do this
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- [Crazy Disk Encoding
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@@ -1,10 +1,11 @@
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#ifndef APPLE2_H
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#define APPLE2_H
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#define MAC_SECTOR_RECORD 0xd5aa96
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#define MAC_DATA_RECORD 0xd5aaad
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#define APPLE2_SECTOR_RECORD 0xd5aa96
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#define APPLE2_DATA_RECORD 0xd5aaad
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#define MAC_SECTOR_LENGTH 524 /* yes, really */
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#define APPLE2_SECTOR_LENGTH 256
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#define APPLE2_ENCODED_SECTOR_LENGTH 342
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class Sector;
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class Fluxmap;
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@@ -23,99 +23,38 @@ static int decode_data_gcr(uint8_t gcr)
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};
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/* This is extremely inspired by the MESS implementation, written by Nathan Woods
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* and R. Belmont: https://github.com/mamedev/mame/blob/4263a71e64377db11392c458b580c5ae83556bc7/src/lib/formats/ap_dsk35.cpp
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* and R. Belmont: https://github.com/mamedev/mame/blob/7914a6083a3b3a8c243ae6c3b8cb50b023f21e0e/src/lib/formats/ap2_dsk.cpp
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*/
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static std::vector<uint8_t> decode_crazy_data(const uint8_t* inp, int& status)
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{
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std::vector<uint8_t> output;
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std::vector<uint8_t> output(APPLE2_SECTOR_LENGTH);
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static const int LOOKUP_LEN = MAC_SECTOR_LENGTH / 3;
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uint8_t b1[LOOKUP_LEN + 1];
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uint8_t b2[LOOKUP_LEN + 1];
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uint8_t b3[LOOKUP_LEN + 1];
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for (int i=0; i<=LOOKUP_LEN; i++)
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uint8_t checksum = 0;
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for (unsigned i = 0; i < APPLE2_ENCODED_SECTOR_LENGTH; i++)
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{
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uint8_t w4 = *inp++;
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uint8_t w1 = *inp++;
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uint8_t w2 = *inp++;
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uint8_t w3 = (i != 174) ? *inp++ : 0;
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checksum ^= decode_data_gcr(*inp++);
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b1[i] = (w1 & 0x3F) | ((w4 << 2) & 0xC0);
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b2[i] = (w2 & 0x3F) | ((w4 << 4) & 0xC0);
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b3[i] = (w3 & 0x3F) | ((w4 << 6) & 0xC0);
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if (i >= 86)
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{
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/* 6 bit */
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output[i - 86] |= (checksum << 2);
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}
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else
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{
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/* 3 * 2 bit */
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output[i + 0] = ((checksum >> 1) & 0x01) | ((checksum << 1) & 0x02);
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output[i + 86] = ((checksum >> 3) & 0x01) | ((checksum >> 1) & 0x02);
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if ((i + 172) < APPLE2_SECTOR_LENGTH)
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output[i + 172] = ((checksum >> 5) & 0x01) | ((checksum >> 3) & 0x02);
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}
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}
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/* Copy from the user's buffer to our buffer, while computing
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* the three-byte data checksum. */
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uint32_t c1 = 0;
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uint32_t c2 = 0;
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uint32_t c3 = 0;
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unsigned count = 0;
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for (;;)
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{
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c1 = (c1 & 0xFF) << 1;
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if (c1 & 0x0100)
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c1++;
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uint8_t val = b1[count] ^ c1;
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c3 += val;
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if (c1 & 0x0100)
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{
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c3++;
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c1 &= 0xFF;
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}
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output.push_back(val);
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val = b2[count] ^ c3;
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c2 += val;
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if (c3 > 0xFF)
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{
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c2++;
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c3 &= 0xFF;
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}
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output.push_back(val);
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if (output.size() == 524)
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break;
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val = b3[count] ^ c2;
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c1 += val;
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if (c2 > 0xFF)
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{
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c1++;
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c2 &= 0xFF;
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}
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output.push_back(val);
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count++;
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}
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uint8_t c4 = ((c1 & 0xC0) >> 6) | ((c2 & 0xC0) >> 4) | ((c3 & 0xC0) >> 2);
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c1 &= 0x3f;
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c2 &= 0x3f;
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c3 &= 0x3f;
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c4 &= 0x3f;
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uint8_t g4 = *inp++;
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uint8_t g3 = *inp++;
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uint8_t g2 = *inp++;
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uint8_t g1 = *inp++;
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if ((g4 == c4) && (g3 == c3) && (g2 == c2) && (g1 == c1))
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status = Sector::OK;
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checksum &= 0x3f;
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uint8_t wantedchecksum = decode_data_gcr(*inp);
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status = (checksum == wantedchecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
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return output;
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}
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uint8_t decode_side(uint8_t side)
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{
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/* Mac disks, being weird, use the side byte to encode both the side (in
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* bit 5) and also whether we're above track 0x3f (in bit 6).
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*/
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return !!(side & 0x40);
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}
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uint8_t combine(uint16_t word)
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{
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return word & (word >> 7);
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@@ -140,7 +79,7 @@ SectorVector Apple2Decoder::decodeToSectors(
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uint32_t signature = read_be24(&rawbytes[0]);
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switch (signature)
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{
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case MAC_SECTOR_RECORD:
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case APPLE2_SECTOR_RECORD:
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{
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uint8_t volume = combine(read_be16(&rawbytes[3]));
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nextTrack = combine(read_be16(&rawbytes[5]));
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@@ -150,24 +89,16 @@ SectorVector Apple2Decoder::decodeToSectors(
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break;
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}
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case MAC_DATA_RECORD:
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case APPLE2_DATA_RECORD:
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{
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if (!headerIsValid)
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break;
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headerIsValid = false;
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uint8_t inputbuffer[MAC_SECTOR_LENGTH * 8/6 + 5] = {};
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for (unsigned i=0; i<sizeof(inputbuffer); i++)
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{
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auto p = rawbytes.begin() + 4 + i;
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if (p > rawbytes.end())
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break;
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inputbuffer[i] = decode_data_gcr(*p);
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}
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std::vector<uint8_t> clippedbytes(rawbytes);
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clippedbytes.resize(APPLE2_ENCODED_SECTOR_LENGTH + 5);
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int status = Sector::BAD_CHECKSUM;
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auto data = decode_crazy_data(inputbuffer, status);
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auto data = decode_crazy_data(&clippedbytes[3], status);
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auto sector = std::unique_ptr<Sector>(
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new Sector(status, nextTrack, 0, nextSector, data));
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@@ -183,7 +114,7 @@ SectorVector Apple2Decoder::decodeToSectors(
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int Apple2Decoder::recordMatcher(uint64_t fifo) const
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{
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uint32_t masked = fifo & 0xffffff;
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if ((masked == MAC_SECTOR_RECORD) || (masked == MAC_DATA_RECORD))
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if ((masked == APPLE2_SECTOR_RECORD) || (masked == APPLE2_DATA_RECORD))
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return 24;
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return 0;
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}
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@@ -14,11 +14,11 @@
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static StringFlag outputFilename(
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{ "--output", "-o" },
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"The output image file to write to.",
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"mac.img");
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"apple2.img");
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int main(int argc, const char* argv[])
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{
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setReaderDefaultSource(":t=0-79:s=0-1");
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setReaderDefaultSource(":t=0-79:s=0");
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setReaderRevolutions(2);
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Flag::parseFlags(argc, argv);
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