Altos ACS8600 crashes inserting a floppy image

[seal331]

MAME version

0.267 (mame0267)

System information

Windows 11, 64-bit, version 23H2 (22631.3880), 16 GB RAM.

INI configuration details

Doesn't look like I have a mame.ini... is this always the case?

Emulated system/software

Altos ACS8600, both Xenix 2.3's root disk and all known ADX disk dumps showed this issue

Incorrect behaviour

When attempting to insert a floppy converted from IMD using floptool (commandline floptool.exe flopconvert auto mfm ADX8618.IMD ADX8618.MFM), MAME does one of the following:

1. The floppy silentlly doesn't insert
2. MAME crashes
3. MAME indicates that the floppy was inserted successfully but then crashes after system reset

Here is the backtrace:

---

Exception at EIP=00007ff7b369c24c (floppy_image_format_t::generate_track_from_bitstream(int, int, unsigned char const*, int, floppy_image&, int, int)+0x004c): ACCESS VIOLATION
While attempting to read memory at 0000000000000000

RAX=000001d18e5860b0 RBX=0000000000000000 RCX=0000000000000138 RDX=0000000000000000
RSI=00000000000186a0 RDI=0000000000000000 RBP=0000000000000000 RSP=000000523df28da0
R8=000001d199fee8e0 R9=00000000000186a0 R10=0000000000000000 R11=0000000000000246
R12=0000000000001d40 R13=000001d1905a44f0 R14=000000000000004e R15=000001d199fee8e0

Stack crawl:
000000523df28e20: 00007ff7b369c24c (floppy_image_format_t::generate_track_from_bitstream(int, int, unsigned char const*, int, floppy_image&, int, int)+0x004c)
000000523df28f40: 00007ff7b36aea09 (mfm_format::load(util::random_read&, unsigned int, std::vector<unsigned int, std::allocator > const&, floppy_image&) const+0x01b9)
└─$
000000523df29130: 00007ff7afd522e6 (device_image_interface::finish_loadabi:cxx11+0x0256)
000000523df292e0: 00007ff7afd54f3e (device_image_interface::load_internal[abi:cxx11](std::basic_string_view<char, std::char_traits >, bool, int, util::option_resolution*)+0x018e)
000000523df29370: 00007ff7afd55431 (device_image_interface::load[abi:cxx11](std::basic_string_view<char, std::char_traits >)+0x00f1)
000000523df294b0: 00007ff7b8f4721e (luaopen_lfs+0x907dae)
000000523df29560: 00007ff7b8f479a9 (luaopen_lfs+0x908539)
000000523df295b0: 00007ff7b90fbb20 (luaopen_lfs+0xabc6b0)
000000523df29620: 00007ff7b898d9f5 (luaopen_lfs+0x34e585)
000000523df29730: 00007ff7b78a53c3 (mame_ui_manager::update_and_render(render_container&)+0x01e3)
000000523df29760: 00007ff7b3615130 (emulator_info::draw_user_interface(running_machine&)+0x0020)
000000523df297f0: 00007ff7b37093ae (video_manager::frame_update(bool)+0x021e)
000000523df29860: 00007ff7afbc5063 (screen_device::vblank_begin(int)+0x0233)
000000523df298d0: 00007ff7afbedb8b (device_scheduler::timeslice()+0x014b)
000000523df29a30: 00007ff7afbeacef (running_machine::run(bool)+0x01bf)
000000523df2eff0: 00007ff7b361aa5b (mame_machine_manager::execute()+0x020b)
000000523df2f3d0: 00007ff7b78deb5f (cli_frontend::start_execution(mame_machine_manager*, std::vector<std::__cxx11::basic_string<char, std::char_traits, std::allocator >, std::allocator<std::__cxx11::basic_string<char, std::char_traits, std::allocator > > > const&)+0x03cf)
000000523df2f690: 00007ff7b78df16d (cli_frontend::execute(std::vector<std::__cxx11::basic_string<char, std::char_traits, std::allocator >, std::allocator<std::__cxx11::basic_string<char, std::char_traits, std::allocator > > >&)+0x004d)
000000523df2f6f0: 00007ff7b36150d9 (emulator_info::start_frontend(emu_options&, osd_interface&, std::vector<std::__cxx11::basic_string<char, std::char_traits, std::allocator >, std::allocator<std::__cxx11::basic_string<char, std::char_traits, std::allocator > > >&)+0x0029)
000000523df2fac0: 00007ff7b95d76bc (luaopen_lfs+0xf9824c)
000000523df2fb90: 00007ff7aada13b1 (__tmainCRTStartup+0x0231)
000000523df2fbc0: 00007ff7aada14e6 (mainCRTStartup+0x0016)
000000523df2fbf0: 00007ffa01b1257d (BaseThreadInitThunk+0x001d)
000000523df2fc70: 00007ffa0202af28 (RtlUserThreadStart+0x0028)

Expected behaviour

MAME successfully inserts the floppy.

Steps to reproduce

1. Download https://www.bitsavers.org/bits/Altos/8600/8600_Floppy_Images_Aug2017/ADX/ADX8618.IMD
2. Run "floptool.exe flopconvert auto mfm ADX8618.IMD ADX8618.MFM"
3. Download the ACS8600 required ROMs
4. Prepare the hard drive image with "chdman.exe createhd -o xenix23.vhd -chs 512,8,32 -ss 256" (those are the characteristics of the Quantum Q2040 drive, the largest hard drive provided by Altos for this machine)
5. Start MAME with "mame.exe altos8600 -fd1797:0 8dd -harddisk xenix23.vhd -ui_active -window"
6. Disable all floppy drives except floppy0, enable rs232a (NOT ics:rs232a)
7. Insert the converted floppy
8. Reset the system
9. Quite possibly observe the crash (see Additional Details)

Additional details

This is a bit weird... When I originally installed MAME to test Altos XENIX, it inserted floppies with no complaints. After my PC was shut down for around 36 hours during a trip, I came back to XENIX, attempted to install it again and reliably got one of 3 results documented in the "Incorrect behaviour" section.

The slot configuration is: rs232a set to terminal, floppy0 set to 8dd, ics:rs232a set to terminal. This issue also happens with the following configuration: floppy0 set to 8dd, ics:rs2321a set to terminal, ics:rs2321b set to terminal.