is a small Apple parallel port hard drive emulator based on the PocketBeagle single-board computer and the Cameo 3.3V ⇄ 5V level adaptor cape. The hardware and software described here aim to be a substitute for 5 MB (and also 10 MB) Apple ProFile external hard drives, which were mainly used with Apple /// and Apple Lisa computers.
Cameo/Aphid and associated hardware designs, software materials, and other resources distributed alongside it are all made available for free with NO WARRANTY OF ANY KIND. Any system that interfaces with Cameo/Aphid could suffer malfunction, data loss, physical damage, or other harms. Some of these effects could be permanent and/or unrepairable. If you're not prepared to risk these consequences, don't use Cameo/Aphid.
Additionally: Cameo/Aphid is a new design that incorporates a number of brand new, built-from-scratch software and hardware components. Although considerable effort has been made to build a dependable emulator, Cameo/Aphid still faces the test of time. It is possible, even likely, that some subtle bugs have yet to be discovered and fixed.
Thumbnails link to high-resolution images, which may be helpful to people assembling Cameo/Aphid. These images are not claimed to be illustrative of good soldering technique.
Top and bottom views: PocketBeagle, Cameo, 5V I/O header to DB-25 adaptor.
Angled front and back views: Cameo/Aphid hardware components.
Angled side views: Cameo/Aphid hardware components.
Profile view: Cameo/Aphid hardware installed on an Apple Lisa computer.
A few additional photos are available in a Google Images gallery.
Cameo/Aphid is designed to be used in much the same way as a real ProFile hard drive: it must be on and ready before the computer can be used; once the computer is off again, Cameo/Aphid can be shut down and turned off.
Because Cameo/Aphid is based on the PocketBeagle, a single-board computer that must boot an operating system to function, Cameo/Aphid takes longer to become ready than a dedicated hardware emulator (e.g. X/ProFile, IDEfile) does. Additionally, like any modern computer (including the Apple Lisa), Cameo/Aphid prefers to undergo a shutdown process before power is shut off. To accomplish this at any point after Cameo/Aphid is ready, press the power button and wait for the "chasing lights" pattern (see below) to stop. It should only take a few seconds.
(UPDATE: Full shutdown is not as important on Debian 9.5 and later OS releases, as long as all the optional steps in the installation instructions have been carried out. The pre-made SD card image was made in this way. Robustness to power cuts is one step toward making Cameo/Aphid a suitable replacement for Widget internal hard drives: further details of improvements targeting Widget replacement are below.)
Cameo/Aphid uses the four "user LEDs" on the PocketBeagle to provide a visual indication of its state. The light patterns you are most likely to see are these:
- Just after Cameo/Aphid turns on: The LEDs turn on one-by-one until all four are on.
- While the operating system is booting: One LED is on nearly constantly, another blinks in a "heartbeat" rhythm; a third blinks with SD card access.
- While Cameo/Aphid software is starting up: All four LEDs blink sequentially in a rapid "chasing" or "rotating" pattern. (UPDATE: This step will be skipped if all the non-optional steps in the installation instructions are carried out, or if the pre-made SD card image is used.)
- When Cameo/Aphid is ready: All four LEDs are on constantly.
- When Cameo/Aphid processes a disk command from the Apple: All four LEDs blink off momentarily.
- During the shutdown process: The chasing pattern resumes.
- When Cameo/Aphid is ready for power off: The chasing pattern has frozen; at most one LED is on.
Finally, if Cameo/Aphid has encountered an unrecoverable error, the two central user LEDs will slowly blink on and off. If this happens, try shutting down the device by pressing the power button. Once the blinking stops, or if the power button appears to have no effect after some time, try removing power from Cameo/Aphid and then restoring it.
Cameo/Aphid receives power from an ordinary Micro-B USB cable. Power consumption data is hard to find for the PocketBeagle, but just about any USB power source that can charge a phone reasonably well will probably work. A computer with a USB-A port can supply power as well; don't be surprised by the PocketBeagle's operating system making the PocketBeagle appear to be both a network adaptor and a storage device.
Most installations will connect Cameo/Aphid to the Apple via a short adaptor cable like the one described in the main Cameo README.md. In this configuration, Cameo/Aphid dangles from the Apple's DB-25 socket with no enclosure or physical support. If your Apple is installed on an unpainted metal table or rack, take care that no components or solder joints on the PocketBeagle or Cameo circuit boards rest on any metal surface: stray electrical connections could result.
The electronics on the Cameo level translator cape do not work well with long parallel cables. Little work has been carried out to determine the longest cable that can work with Cameo/Aphid, but lengths between 50cm (20") and "as short as possible" are probably preferable. Cameo/Aphid will work when attached to a Widget hard drive ribbon cable inside a Lisa 2/10. Apple II users should note that a typical Apple II ProFile interface card installation uses a somewhat lengthy cable to connect the card to the parallel port. (Cameo/Aphid has not yet been tested on an Apple II.)
Cameo/Aphid stores data from the simulated hard drive in an ordinary file on the PocketBeagle's microSD card. This file has no metadata and a very simple format: just as a 5 MB ProFile stores 5,175,296 bytes of data, a corresponding hard drive image file is a 5,175,296-byte file; and just as a ProFile block is 532 bytes, each contiguous 532-byte chunk of the image file holds data from one of the simulated drive's blocks. These blocks are arranged sequentially in the file, starting from block $0000 and counting up to block $25FF.
(Aside: neither Cameo/Aphid nor the Apple parallel hard disk protocol itself distinguish between "tag bytes" or "data bytes", even though these divisions of a block are important to Lisas.)
Cameo/Aphid does not require image files to be only 5,175,296 bytes in size. A 10,350,592-byte image file causes Cameo/Aphid to emulate a 10 MB ProFile (complete with the "spare table" data structure that announces it as such). An enormous range of non-standard sizes are also supported: Cameo/Aphid will do its best to serve hard drive image files of any size up to 8,890,613,228 bytes (!), though images larger than a few dozen megabytes have not been tested.
(Note that many operating systems for your Apple will not know what to do with hard drives that have non-standard sizes, and some older operating systems may only work with 5 MB ProFiles.)
A microSD card initialised from the pre-built software image, or any other installation that makes use of a
separate FAT32 partition for drive image storage, can be
plugged into most modern computers and accessed like an ordinary flash drive.
Some computers may show two drives, one called rootfs and another called
CAMEO_APHID: the CAMEO_APHID drive is the home for hard drive images, and
rootfs should be left alone. (Windows users who don't see a drive after
plugging in their microSD cards may need to use the "Disk Management" or
"Create and format hard disk partitions" control panel to assign a drive letter
to the SD card's CAMEO_APHID partition.)
On the CAMEO_APHID drive, hard drive image files are any that end in
.image, with profile.image being the image file that Cameo/Aphid uses on
start-up. It is fine to copy, rename, and otherwise manage hard drive image
files like any other kind of file, but Cameo/Aphid will not work if no file
called profile.image exists.
The operating system that runs on Cameo/Aphid's PocketBeagle computer is a
version of Debian Linux. In standard Cameo/Aphid setups, the CAMEO_APHID
partition is mounted at /usr/local/lib/cameo-aphid. If you have a network
connection to the PocketBeagle, which usually establishes automatically when
you plug a PocketBeagle into a modern computer's USB port, you can use ordinary
communications utilities (typically SSH, SCP) for command line access and file
transfer with the device. (For more guidance on connecting to your
PocketBeagle, see the BeagleBone "Getting Started" guide. You may need to use the IP addresses
192.168.6.2 or 192.168.7.2 instead of the beaglebone.local convenience name.)
In the future, it may become possible to upload and download drive images via a web browser.
Cameo/Aphid allows the Apple to restart or shut down ProFile emulation via specially-formatted writes. The Apple can use this "control writes" mechanism to change the hard drive image file that Cameo/Aphid uses for reads and writes.
The following "control writes" are made to the non-existent sector $FFFFFD, with $FE as the retry count parameter and $AF as the sparing threshold parameter:
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Writing sector data that begins with the null-terminated string "HALT" (i.e.
$48,$41,$4C,$54,$00) causes Cameo/Aphid to cease ProFile emulation. This does not shut down the PocketBeagle itself. When emulation is halted, the four user LEDs will blink sequentially in a rapid "chasing" or "rotating" pattern. -
Writing sector data that begins with "IMAGE:" (i.e.
$49,$4D,$41,$47,$45,$3A) and then continues with the null-terminated name of a file residing in the working directory of the Cameo/Aphid ProFile emulator Python program, causes Cameo/Aphid to restart ProFile emulation with this file as the hard drive image that it uses for reads and writes. For extra safety, the filename must end in ".image". -
Writing any other sector data will cause Cameo/Aphid to restart ProFile emulation with the same hard drive image file that it was using prior to the write.
Restarting ProFile emulation takes less than a second, but no effort has been made to determine what happens if the Apple tries to interact with Cameo/Aphid during this interval.
At present, the only way to get your own Cameo/Aphid is to build one. Finished assemblies are not known to be available anywhere, but since all the Cameo/Aphid-specific software and hardware designs are released into the public domain, anyone is free to build and sell them without seeking anyone's permission or negotiating any license terms. The parts cost for a complete, ready-to-use Cameo/Aphid setup is around $55 for a home hobbyist; manufacture in limited quantities might lower this figure somewhat.
Building Cameo/Aphid "from scratch" requires some proficiency in the following skills:
- Soldering surface-mounted components, including ICs in small (TSSOP) packages with a somewhat narrow (0.65mm) pin pitch.
"Linux stuff": SSH, using the command line,sudo, editing configuration files, that sort of thing.
If you think you might be able to do it, you probably can, with patience.
Cameo/Aphid uses the Texas Instruments TXS0108E series of level translator ICs. A complete parts list for assembling Cameo/Aphid appears in the main Cameo README.md. Nearly all installations will want to use the short adaptor cable described there so that Cameo/Aphid can dangle from a parallel port on the Apple.
This diagram shows the locations and values of all of the SMD components that should be installed on the Cameo PCB to support Aphid:
The jumpers on the "plugboard" pads establish connections between the 5V I/O header pins and the level translator chip. The current design uses 100Ω terminating resistors for these connections to support longer cables between Cameo/Aphid and the Apple; in general, though, shorter cables are preferable. Take care to replicate the positioning of all components exactly---the plugboard pads are tightly spaced, and it's especially easy to put a jumper in the wrong place.
The main Cameo README.md has more detailed assembly information.
When building a DB-25 port adaptor to connect Cameo to the Apple: sometimes the Apple's parallel port will have plastic material or a metal shim blocking pin 7, which is unused. If this is the case for your system, remove pin 7 (the centre pin in the top, wider row of pins) from the adaptor's DB-25 plug with a pair of pliers. Some force may be required.
The easiest way to install Cameo/Aphid software on a microSD card is to "flash" a pre-built software image onto the card: it requires no skill with "Linux stuff". Download a software image (made with the instructions below) from this link (note: a circa 600 MB file, give or take several dozen MB), then follow these instructions on using Etcher to install the image onto a good quality microSD card (4GB or more, preferably Class 10/U1/V10 or better). Once flashed, the card can be plugged into the PocketBeagle, and Cameo/Aphid will be ready for use, appearing to the Apple as an empty (uninitialised) ProFile. The following instructions can then be ignored.
(Technical note: The pre-built software image stores the ProFile drive image on
a separate 512 MB FAT32 partition with the label CAMEO_APHID, which it mounts
at /usr/local/lib/cameo-aphid. Only changes to files in this directory will
persist between PocketBeagle power cycles and reboots; all changes to all other
files and directories are temporary.)
The Cameo/Aphid software comprises
- firmware programs for each of the PocketBeagle's two PRU-ICSS real time I/O coprocessors ("PRUs" for short)
- a Python program that runs on the PocketBeagle's main processor, interpreting sector read/write commands from the Apple and applying them to a hard drive image file
- a Python plugin module for the program that provides a "magic blocks" facility: reads and writes to these blocks can modify the behaviour of the emulator or support a variety of operations unrelated to ordinary hard drive data storage
- a collection of Python module plugins that exploit this capability to provide a system information service, a file management service, and a key/value store
- a software program for the Apple Lisa, taking the form of a bootable hard drive image, that uses the "magic block" plugins to provide a versatile text-based interface for selecting and managing hard drive images.
The software targets the following BeagleBone.org Debian Linux disk images:
Debian 10.3 2020-04-06 4GB SD IoT(Not recommended: see below)Debian 10.0 2019-07-07 4GB SD IoTDebian 9.9 2019-08-03 4GB SD IoTDebian 9.5 2018-10-07 4GB SD IoTDebian 9.5 2018-08-30 4GB SD IoTDebian 9.4 2018-06-17 4GB SD IoTDebian 9.3 2018-03-05 4GB SD IoT
available here. If none of these are listed under "Recommended Debian images", look for them under "Older Debian images" further down on the page. Newer images may work but have not been tested.
(The Debian 10.3 2020-04-06 4GB SD IoT image is not recommended as it lacks
support for the optional power-off robustness mechanism described
below. A feature request to restore this support
in future BeagleBone.org Debian Linux disk images has been filed.)
Follow these steps to set up the Cameo/Aphid software on your PocketBeagle:
Download one of the Debian Linux disk images specified above from the BeagleBoard.org Latest Firmware Images page (preferably the Debian 9.9 image). Follow the instructions to install it on a good quality microSD card. (The PocketBeagle used to develop the Cameo/Aphid software had a card with a Class 10 speed class rating.)
Debian 9.3 2018-03-05 4GB SD IoT Debian Linux disk image.
Boot your PocketBeagle and connect to it via SSH. As above, this usually
entails plugging the PocketBeagle into your computer's USB port and logging in
to beaglebone.local as user debian with password temppwd. For more
guidance on connecting to your PocketBeagle, see the BeagleBone "Getting
Started" guide.
Once in, edit the file /boot/uEnv.txt with superuser privileges. Find the
line containing this text:
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo
and just beneath it, add a new line with the following text:
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-9-TI-00A0.dtbo
Take care to avoid typos or copy/paste errors: mistakes in /boot/uEnv.txt can
leave your microSD card unbootable, and you'd need to start over from Step 1.
Copy this directory and all of its contents to the PocketBeagle (usually
accomplished via SCP to beaglebone.local). It's fine to place the copy
anywhere in the home directory of the debian user.
Log back into your PocketBeagle and cd into the copy of this directory. Begin
the compile by typing make. Compilation of the firmware and decompression of
the drive image (a 5,175,296-byte file called profile.image preloaded with the
Cameo/Aphid selector, unpacked from selector/selector.image.zip) takes a couple dozen seconds.
This optional step establishes a separate FAT32 partition on the SD card for
ProFile drive image storage---required for setting up the robustness to power
failure described in Step 8. First, from the directory created by Step 3,
execute the script setup_dos_partition_part1.sh with superuser privileges,
optionally with a size argument in bytes (a 512 MB partition is created by
default). When this completes, reboot the PocketBeagle. Log in again, return to
the same directory, and execute the script setup_dos_partition_part2.sh.
Together, these scripts modify the SD card's partition table to add a
partition, create a mount point for the partition at
/usr/local/lib/cameo-aphid, create a FAT32 filesystem on the partition, and
direct the OS to mount the new partition there on boot.
From the directory created by Step 3, execute the command make install with
superuser privileges. This command creates a permanent installation directory
for the Cameo/Aphid software and drive image, then installs a file that tells
the PocketBeagle to configure and start the entire Cameo/Aphid emulator system
on boot. The specific steps that make install performs are:
- Copy the PRU-ICSS firmware files
aphd_pru0_datapump.fwandaphd_pru1_control.fwto the/lib/firmwaredirectory. - Copy those files to
/lib/firmwarea second time, but use the filenamesam335x-pru0-fwandam335x-pru1-fw, which causes the kernel to load the firmware into the PRU-ICSS coprocessors at boot time. - Copy the device tree overlay file
PB-CAMEO-APHID.dtboto the/lib/firmwaredirectory. - Create the directory
/usr/local/lib/cameo-aphid(if not already present) and copy the drive image fileprofile.imageand the Python programprofile.pyinside. - Copy the
cameo-aphid.serviceservice script to/lib/systemd/system.
With superuser privileges, and in the directory created by Step 3, run the
setup_device_tree_overlay.sh script. This tells the Linux kernel running on
the PocketBeagle to load the PB-CAMEO-APHID.dtbo device tree overlay on
startup, which causes the PocketBeagle to configure its low-level facilities at
boot time for communication with an Apple through the Cameo level translator
cape. (Specifically, it primarily sets up the "pinmux", which controls how
devices built into the PocketBeagle like the PRUs connect to physical
PocketBeagle pins.)
With superuser privileges, execute the command systemctl enable cameo-aphid.
Basic software installation is complete after this step. The next time the PocketBeagle boots, the Cameo/Aphid emulator should be ready to emulate a 5 MB Apple ProFile hard drive. See the Usage section of this file for usage instructions.
The following steps are optional, but useful.
With superuser privileges, and in the directory created by Step 3, run the
scripts setup_trim_services.sh and setup_trim_misc.sh. This disables some
PocketBeagle system facilities that aren't useful for hard disk emulation,
which shaves a few seconds off the time it takes Cameo/Aphid to be ready after
power-on.
With superuser privileges, and in the directory created by Step 3, run the
setup_os_config_changes.sh script, which applies miscellaneous beneficial
changes to the operating system's configuration. Refer to the contents of the
script for details on what the changes do and why.
Only if Step 5 has been carried out, run the script setup_overlayroot.sh with
superuser privileges. This causes the PocketBeagle to boot into a mode where
files on the root filesystem cannot be changed; instead, changes are stored
temporarily in the PocketBeagle's RAM and are lost when the PocketBeagle shuts
down or reboots. The separate filesystem for drive images set up in Step 5 is
not affected and writes to emulated ProFiles will still be saved.
This step makes it safer to shut off power to Cameo/Aphid without undergoing the formal shutdown process triggered by pressing the power button. The root filesystem cannot be damaged by uncommitted writes, and changes to the FAT32 filesystem containing drive image data are frequently committed to the SD card.
The information in this section is not necessary to build or use Cameo/Aphid, but may be of interest to people interested in making modifications or investigating similar applications.
Cameo/Aphid takes advantage of the PocketBeagle's PRU-ICSS coprocessors ("PRUs" for short) to achieve a dependable implementation of the Apple parallel port hard drive protocol. Like the I/O subsystems on modern PCs or the channel controllers on mainframes of yore, the PRUs handle the timing-sensitive low-level details of the protocol so that the main processor can attend to various custodial tasks on its own schedule.
The PocketBeagle's AM3358 SoC includes two PRUs. Each PRU has a different pattern of direct connectivity to the pins of the PocketBeagle's two expansion headers. PRU 0 can access eight pins in either the input or output direction plus four more as inputs only and two more as outputs only; PRU 1 can access six pins in either the input or output direction plus two more as inputs only. Cameo's pair of level translator ICs can accommodate only 16 signal lines altogether, so of these 22 pins, Cameo passes through all 14 two-way signals, one PRU 0 input-only line, and one PRU 0 output-only line.
Inspired by this arrangement and the nature of the Apple parallel port hard drive protocol, the overall Cameo/Aphid design allocates PRU 0 to handle clocked data transfer and calculation of the (odd) parity signal for the parallel port's eight bidirectional I/O lines, and it allocates PRU 1 to handle the parallel port's three other control lines. Notionally, PRU 1 supervises the handling of all transactions with the Apple; PRU 0 is the "data pump" that streams bytes to and from the Apple on PRU 1's request, while the Python program running on the PocketBeagle's main ARM processor loads and saves block data in the drive image file whenever PRU 1 instructs it to do so.
Although PRU 0 can directly access eight of the I/O pins as either inputs or outputs, a PRU cannot select or change which of these "direct access" modes is in effect. Unfortunately, that means that these modes aren't suitable for bidirectional I/O, even though Cameo is otherwise well-organised to facilitate this: PRU 0 simply can't alternate between sending and receiving data via direct access. So, to manage the eight data lines, PRU 0 falls back to using the AM3358's GPIO registers---a method available to either PRU. Still, the division of labour between both PRUs is convenient: it allows PRU 0 to respond quickly to the Apple's \PSTRB clocking signal and to compute the correct value for \PPARITY (both accessed by PRU 0 directly) whilst PRU 1 and the ARM are busy doing other things.
PRU 0 and PRU 1 do most of their information sharing through the PRU shared memory region, with data transfer requests and completions signaled via interrupts. Communication between PRU 1 and the ARM uses Linux's RPMsg I/O framework, and because RPMsg messages can be no larger than 512 bytes, multiple messages are necessary to transfer block data between the ARM and the PRUs.
All three major Cameo/Aphid software/firmware components are extensively commented, so further detail here may be redundant. Good starting places for reading Cameo/Aphid source code are:
- profile.py: the entire Python program that runs on the ARM.
- aphd_pru0_datapump.asm: the entire source code for the PRU 0 "data pump" firmware.
- aphd_pru1_control.cc: core of the PRU 1 "control" firmware.
Potential future improvements and new features for Cameo/Aphid include:
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Widget emulation (hard, since many more low-level hard drive commands are required for complete emulation).
-
Support for Lisa 2/10 drive bay installation: largely complete.
-
✔️ Increased robustness to power cuts allow Cameo/Aphid to operate within the enclosed drive bay, even though a Lisa powering down can shut down internal hard drives without warning.
-
✔️ The longer ribbon cable that the 2/10 uses to connect to the Widget in the drive bay causes signal quality issues that can lead to malfunctions, likely due to ringing or reflections that can confuse the TXS0108E level adaptor ICs about signal direction. Inline 100Ω terminating resistors on all Cameo signal lines except PEX1, PEX2, and PEX3 appear to dampen the ringing well enough for Cameo/Aphid to work.
-
✔️ When a Lisa 2/10 is powered on, it will attempt to boot from its internal parallel port in around 22 seconds. For Cameo/Aphid installed internally to make use of the Widget hard drive's power supply, it must boot and be ready to emulate a hard drive in a similar amount of time: if it's too slow, the Lisa will present a boot error and require user input. Improvements to the Cameo/Aphid boot procedure now reduce startup time below the critical threshold required for automatic booting.
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🤷♂️ Finally, some substitute for the green hard drive status LED should be devised.
-
-
A web browser interface for hard drive image file management: by plugging Cameo/Aphid into a modern computer and visiting a designated web address, the user can upload and download hard drive image files to an image library, as well as select an "active" image that Cameo/Aphid serves to the Apple. (Even a relatively small microSD card could easily store several thousand hard drive image files.)
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An Aphid-specific level translator PCB design instead of configurable, multi-purpose Cameo and its plugboard: it may be possible for the PCB to be a two-layer design, offering significant cost advantages. An integral DB-25 plug connector could be an additional feature.
To the fullest extent possible, Cameo/Aphid is released into the public domain. Nobody owns Cameo/Aphid.
The modified linker command files for the PRU 0 and PRU 1 firmware bear copyright statements by Texas Instruments and are mostly generated automatically by TI's Code Composer Studio IDE.
All other source code files associated with Aphid are forfeited into the public domain with no warranty. For details, see the LICENSE file.
Apple, ProFile, and Lisa are Apple Inc. trademarks. PocketBeagle, BeagleBone, and BeagleBone.org are BeagleBone.org trademarks. Sitara and Code Composer Studio are Texas Instruments Inc. trademarks.
It would not have been possible for me to create Cameo/Aphid without the help of the following people and resources:
- Dr. Patrick Schäfer, whose IDEfile and UsbWidEx project pages were invaluable to the project (as were actual UsbWidEx and IDEfile devices of my own).
- bitsavers.org's archived technical documentation.
- The Sitara Processors Forum on the TI E2E Community.
- Blog posts and other materials by Dr. Andrew Wright, Jason Kridner, Dr. Mark A. Yoder, Ken Shirriff, and others.
- Encyclopedic references like the AM335x Technical Reference Manual, the PRU Assembly Instruction User Guide, the AM335x PRU-ICSS Reference Guide, the PRU Assembly Language Tools User's Guide, the PRU Optimizing C/C++ Compiler v2.2 User's Guide, and the PocketBeagle System Reference Manual.
- Pointers from zmatt of the
#beagleIRC channel on irc.freenode.net. - The entire LisaList community.
- Torbjörn Nordlindh and Stefan Wärn for information and testing leading to Apple /// and recent macOS compatibility.
- Anonymous friends.
11 August 2018: Initial release. (Tom Stepleton, stepleton@gmail.com, London)
4 October 2018: Debian 9.5 support, power-cut resilience, boot time, SD card longevity (Tom Stepleton)
- Debian 9.5 support: adapt to changes to resource table field names and layout.
- Power-cut resilience: introduce a separate FAT32 partition for drive images.
- Power-cut resilience: add overlayfs protection for root filesystem.
- Boot time: disable unused Linux services.
- SD card longevity: only sync drive image changes every four seconds.
20 October 2018: Update to the BeagleBoard.org 2018-10-07 Debian 9.5 image. (Tom Stepleton)
7 December 2018: Inline 100Ω terminating resistors on signal lines for improved performance with longer cables. (Tom Stepleton)
6 November 2019: Debian 9.9 support. (Tom Stepleton)
12 January 2020: Upgraded profile.py to Python 3.5; the Apple can now command
the emulator to use a different boot image or cease emulation. (Tom Stepleton)
24 January 2021: Many changes, including the "magic blocks" plugin mechanism, the Selector program, and a bug fix that allows a Lisa to boot reliably from a Cameo/Aphid attached to the upper port of a 2-port parallel expansion card. (Tom Stepleton)
3 February 2021: Automatic firmware loading on startup and the addition of a device tree overlay dramatically reduce boot times, making it feasible to install Cameo/Aphid inside a Lisa 2/10. (Tom Stepleton)
6 February 2021: 10 MB ProFile emulation and support for arbitrarily-sized drive images. (Tom Stepleton)
15 February 2021: Eliminate timeouts in PRU0 firmware (and add timeouts to PRU1 firmware in strategic places) for better MacWorks compatibility. (Tom Stepleton)
19 June 2021: Stop requiring writes to be 532 bytes long (some Apple /// OSs write only 512 bytes). Manually apply changes like the ones from this patch to the 10.0 IoT image for USB compatibility with modern MacOS. (Tom Stepleton)