Breaking Eggs And Making Omelettes

Les articles publiés sur le site

• My SBC Collection

  31 décembre 2023, par Multimedia Mike — General

  Like many computer nerds in the last decade, I have accumulated more than a few single-board computers, or “SBCs”, which are small computers based around a system-on-a-chip (SoC) that nearly always features an ARM CPU at its core. Surprisingly few of these units are Raspberry Pi units, though that brand has come to exemplify and dominate the product category.

  Also, as is the case for many computer nerds, most of these SBCs lay fallow for years at a time. Equipped with an inexpensive lightbox that I procured in the last year, I decided I could at least create glamour shots of various units and catalog them in a blog post.

  While Raspberry Pi still enjoys the most mindshare far and away, and while I do have a few Raspberry Pi units in my inventory, I have always been a bigger fan of the ODROID brand, which works with convenient importers around the world (in the USA, I can vouch for Ameridroid, to whom I’ve forked over a fair amount of cash for these computing toys).

  As mentioned, Raspberry Pi undisputedly has the most mindshare of all these SBC brands and I often wonder why… and then I immediately remind myself that it has the biggest ecosystem, and has a variety of turnkey projects and applications (such as Pi-hole and PiVPN) that promise a lower barrier to entry — as well as a slightly lower price point — than some of these other options. ODROID had a decent ecosystem for awhile, especially considering the monthly ODROID Magazine, though that ceased publication in July 2020. The Raspberry Pi and its variants were famously difficult to come by due to the global chip shortage from 2021-2023. Meanwhile, I had no trouble procuring these boards during the same timeframe.

  So let’s delve into the collection…
  

  Cubieboard
  The Raspberry Pi came out in 2012 and by 2013 I was somewhat coveting one to hack on. Finally! An accessible ARM platform to play with. I had heard of the BeagleBoard for years but never tried to get my hands on one. I was thinking about taking the plunge on a new Raspberry Pi, but a colleague told me I should skip that and go with this new hotness called the Cubieboard, based on an Allwinner SoC. The big value-add that this board had vs. a Raspberry Pi was that it had a SATA adapter. Although now that it has been a decade, it only now occurs to me to quander whether it was true SATA or a USB-to-SATA bridge. Looking it up now, I’m led to believe that the SoC supported the functionality natively.

  Anyway, I did get it up and running but never did much with it, thus setting the tone for future SBC endeavors. No photos because I gave it to another tech enthusiast years ago, whose SBC collection dwarfs my own.

  ODROID-XU4
  I can’t recall exactly when or how I first encountered the ODROID brand. I probably read about it on some enthusiast page or another circa 2014 and decided to try one out. I eventually acquired a total of 3 of these ODROID-XU4 units, each with a different case, 1 with a fan and 2 passively-cooled:

  

  Collection of ODROID-XU4 SBCs

  This is based on the Samsung Exynos 5422 SoC, the same series as was used in their Note 3 phone released in 2013. It has been a fun chip to play with. The XU4 was also my first introduction to the eMMC storage solution that is commonly supported on the ODROID SBCs (alongside micro-SD). eMMC offers many benefits over SD in terms of read/write speed as well as well as longevity/write cycles. That’s getting less relevant these days, however, as more and more SBCs are being released with direct NVMe SSD support.

  I had initially wanted to make a retro-gaming device built on this platform (see the handheld section later for more meditations on that). In support of this common hobbyist goal, there is this nifty case XU4 case which apes the aesthetic of the Nintendo N64:

  

  ODROID-XU4 N64-style case

  It even has a cool programmable LCD screen. Maybe one day I’ll find a use for it.

  For awhile, one of these XU4 units (likely the noisy, fan-cooled one) was contributing results to the FFmpeg FATE system.

  While it features gigabit ethernet and a USB3 port, I once tried to see if I could get 2 Gbps throughput with the unit using a USB3-gigabit dongle. I had curious results in that the total amount of traffic throughput could never exceed 1 Gbps across both interfaces. I.e., if 1 interface was dealing with 1 Gbps and the other interface tried to run at 1 Gbps, they would both only run at 500 Mbps. That remains a mystery to me since I don’t see that limitation with Intel chips.

  Still, the XU4 has been useful for a variety of projects and prototyping over the years.

  ODROID-HC2 NAS
  I find that a lot of my fellow nerds massively overengineer their homelab NAS setups. I’ll explore this in a future post. For my part, people tend to find my homelab NAS solution slightly underengineered. This is the ODROID-HC2 (the “HC” stands for “Home Cloud”):

  

  ODROID-HC2 NAS

  It has the same guts as the ODROID-XU4 except no video output and the USB3 function is leveraged for a SATA bridge. This allows you to plug a SATA hard drive directly into the unit:

  

  ODROID-HC2 NAS uncovered

  Believe it or not, this has been my home NAS solution for something like 6 or 7 years now– I don’t clearly remember when I purchased it and put it into service.

  But isn’t this sort of irresponsible? What about a failure of the main drive? That’s why I have an external drive connected for backing up the most important data via rsync:

  

  ODROID-HC2 NAS backup enclosure

  The power consumption can’t be beat– Profiling for a few weeks of average usage worked out to 4.5 kWh for the ODROID-HC2… per month.

  ODROID-C2
  I was on a kick of ordering more SBCs at one point. This is the ODROID-C2, equipped with a 64-bit Amlogic SoC:

  

  ODROID-C2

  I had this on the FATE farm for awhile, performing 64-bit ARM builds (vs. the XU4’s 32-bit builds). As memory serves, it was unreliable and would occasionally freeze up.

  Here is a view of the eMMC storage through the bottom of the translucent case:

  

  Bottom of ODROID-C2 with view of eMMC storage

  ODROID-N2+
  Out of all my ODROID SBCs, this is the unit that I long to “get back to” the most– the ODROID-N2+:

  

  ODROID-N2+

  Very capable unit that makes a great little desktop. I have some projects I want to develop using it so that it will force me to have a focused development environment.

  Raspberry Pi
  Eventually, I did break down and get a Raspberry Pi. I had a specific purpose in mind and, much to my surprise, I have stuck to it:

  

  Original Raspberry Pi

  I was using one of the ODROID-XU4 units as a VPN gateway. Eventually, I wanted to convert the XU4 to something else and I decided to run the VPN gateway as an appliance on the simplest device I could. So I procured this complete hand-me-down unit from eBay and went to work. This was also the first time I discovered the DietPi distribution and this box has been in service running Wireguard via PiVPN for many years.

  I also have a Raspberry Pi 3B+ kicking around somewhere. I used it as a Steam Link device for awhile.

  SOPINE + Baseboard
  Also procured when I was on this “let’s buy random SBCs” kick. The Pine64 SOPINE is actually a compute module that comes in the form factor of a memory module.

  

  Pine64 SOPINE Compute Module

  Back to using Allwinner SoCs. In order to make this thing useful, you need to place it in something. It’s possible to get a mini-ITX form factor board that can accommodate 7 of these modules. Before going to that extreme, there is this much simpler baseboard which can also use eMMC for storage.

  

  Baseboard with SOPINE, eMMC, and heat sinks

  I really need to find an appropriate case for this one as it currently performs its duty while sitting on an anti-static bag.

  NanoPi NEO3
  I enjoy running the DietPi distribution on many of these SBCs (as it’s developed not just for Raspberry Pi). I have also found their website to be a useful resource for discovering new SBCs. That’s how I found the NanoPi series and zeroed in on this NEO3 unit, sporting a Rockchip SoC, and photographed here with some American currency in order to illustrate its relative size:

  

  NanoPi NEO3

  I often forget about this computer because it’s off in another room, just quietly performing its assigned duty.

  MangoPi MQ-Pro
  So far, I’ve heard of these fruits prepending the Greek letter pi for naming small computing products:

  • Raspberry – the O.G.
  • Banana – seems to be popular for hobbyist router/switches
  • Orange
  • Atomic
  • Nano
  • Mango

  Okay, so the AtomicPi and NanoPi names don’t really make sense considering the fruit convention.

  Anyway, the newest entry is the MangoPi. These showed up on Ameridroid a few months ago. There are 2 variants: the MQ-Pro and the MQ-Quad. I picked one and rolled with it.

  

  MangoPi MQ-Pro pieces arrive

  When it arrived, I unpacked it, assembled the pieces, downloaded a distro, tossed that on a micro-SD card, connected a monitor and keyboard to it via its USB-C port, got the distro up and running, configured the wireless networking with a static IP address and installed sshd, and it was ready to go as a headless server for an edge application.

  

  MangoPi MQ-Pro components, ready for assembly

  The unit came with no instructions that I can recall. After I got it set up, I remember thinking, “What is wrong with me? Why is it that I just know how to do all of this without any documentation?”

  

  MangoPi MQ-Pro in first test

  Only after I got it up and running and poked around a bit did I realize that this SBC doesn’t have an ARM SoC– it’s a RISC-V SoC. It uses the Allwinner D1, so it looks like I came full circle back to Allwinner.

  

  MangoPi MQ-Pro with more US coinage for scale

  So I now have my first piece of RISC-V hobbyist kit, although I learned recently from Kostya that it’s not that great for multimedia.

  Handheld Gaming Units
  The folks at Hardkernel have also produced a series of handheld retro-gaming devices called ODROID-GO. The first one resembled the original Nintendo Game Boy, came as a kit to be assembled, and emulated 5 classic consoles. It also had some hackability to it. Quite a cool little device, and inexpensive too. I have since passed it along to another gaming enthusiast.

  Later came the ODROID-GO Advance, also a kit, but emulating more devices. I was extremely eager to get my hands on this since it could emulate SNES in addition to NES. It also features a headphone jack, unlike the earlier model. True to form, after I received mine, it took me about 13 months before I got around to assembling it. After that, the biggest challenge I had was trying to find an appropriate case for it.

  

  ODROID-GO Advance with case and headphones

  Even though it may try to copy the general aesthetic and form factor of the Game Boy Advance, cases for the GBA don’t fit this correctly.

  Further, Hardkernel have also released the ODROID-GO Super and Ultra models that do more and more. The Advance, Super, and Ultra models have powerful SoCs and feature much more hackability than the first ODROID-GO model.

  I know that the guts of the Advance have been used in other products as well. The same is likely true for the Super and Ultra.

  Ultimately, the ODROID-GO Advance was just another project I assembled and then set aside since I like the idea of playing old games much more than actually doing it. Plus, the fact has finally crystalized in my mind over the past few years that I have never enjoyed handheld gaming and likely will never enjoy handheld gaming, even after I started wearing glasses. Not that I’m averse to old Game Boy / Color / Advance games, but if I’m going to play them, I’d rather emulate them on a large display.

  The Future
  In some of my weaker moments, I consider ordering up certain Banana Pi products (like the Banana Pi BPI-R2) with a case and doing my own router tricks using some open source router/firewall solution. And then I remind myself that my existing prosumer-type home router is doing just fine. But maybe one day…

  The post My SBC Collection first appeared on Breaking Eggs And Making Omelettes.

• Dreamcast Finds

  15 avril 2022, par Multimedia Mike — Sega Dreamcast

  Pursuant to my recent post about finally understanding how Sega Dreamcast GD-ROM rips are structured, I was able to prepare the contents of various demo discs in a manner that makes exploration easy via the Internet Archive. This is due to the way that IA makes it easy to browse archives such as ZIP or ISO files (anything that 7zip knows how to unpack), and also presents the audio tracks for native playback directly through the web browser.

  These are some of the interesting things I have found while perusing the various Dreamcast sampler discs.

  Multimedia Formats
  First and foremost: Multimedia-wise, SFD and ADX files abound on all the discs. SFD files are Sofdec, a middleware format used for a lot of FMV on Dreamcast games. These were little more than MPEG video files with a non-MPEG (ADPCM instead) audio codec. VLC will usually play the video portions of these files but has trouble detecting the audio. It’s not for lack of audio codec support because it can play the ADX files just fine.
  

  It should be noted that Dreamcast Magazine Disc 11 has an actual .mpg file (as opposed to a .sfd file) that has proper MPEG audio instead instead of ADX ADPCM.

  The only other multimedia format I know of that was used in any Dreamcast games was 4XM, used on Alone In The Dark: The New Nightmare. I wrote a simple C tool a long time to recover these files from a disc image I extracted myself. Rather than interpreting the ISO-9660 filesystem, the tool just crawled through the binary blob searching for ‘4XMV’ file signatures and using length data within the files for extraction.

  Also, there are plentiful PVR files (in reference to the PowerVR2 GPU hardware that the DC uses) which ‘file’ dutifully identifies as “Sega PVR image”. There are probably tools to view them. It doesn’t appear to be a complicated format.

  Scripting
  I was fascinated to see Lua files on at least one of the discs. It turns out that MDK 2 leverages the language, as several other games do. But it was still interesting to see the .lua files show up in the Dreamcast version as well.

  That Windows CE Logo
  Every Sega Dreamcast is famously emblazoned with a logo mentioning Microsoft Windows CE:

  
  
  

  It has confused many folks. It also confused me until this exploratory exercise. Many would wonder if the Dreamcast booted up into some Windows CE OS environment that then ran the game, but that certainly wasn’t it. Indeed, Dreamcast was one of the last consoles that really didn’t have any kind of hypervisor operating system managing everything.

  I found a file called rt2dc.exe on one sampler disc. At first, I suspected that this was a development utility for Windows to convert some “RT” graphical format into a format more suitable for the Dreamcast. Then, ‘file’ told me that it was actually a Windows EXE but compiled for the Hitachi SH-4 CPU (the brain inside the DC). Does the conversion utility run on the Dreamcast itself? Then I analyzed the strings inside the binary and saw references to train stations. That’s when it started to click for me that this was the binary executable for the demo version of Railroad Tycoon 2: Gold Edition, hence “rt2dc.exe”. Still, this provides some insight about whether Dreamcast “runs” Windows. This binary was built against a series of Windows CE libraries. The symbols also imply DirectX compatibility.

  Here is a page with more info about the WinCE/DirectX variant for the Sega Dreamcast. It seems that this was useful for closing the gap between PC and DC ports of games (i.e., being able to re-use more code between the 2 platforms). I guess this was part of what made Dreamcast a dry run for the DirectXbox (later Xbox).

  Here is a list of all the Dreamcast games that are known to use Windows CE.

  Suddenly, I am curious if tools such as IDA Pro or Ghidra can possibly open up Windows CE binaries that contain SH-4 code. Not that I’m particularly interested in reverse engineering any algorithms locked up in Dreamcast land.

  Tomb Raider Easter Egg
  The volume 6 sampler disc has a demo of Tomb Raider: The Last Revelation. While inspecting the strings, I found an Easter egg. I was far from the first person to discover it, though, as seen on this The Cutting Room Floor wiki page (look under “Developer Message”). It looks like I am the first person to notice it on the Dreamcast version. It shows up at offset 0xE3978 in the Dreamcast (demo version) binary, if anyone with permissions wants to update the page.

  Web Browser
  Then there’s the Web Browser for Sega Dreamcast. It seemed to be included on a lot of these sampler discs. But only mentioning the web browser undersells it– the thing also bundled an email client and an IRC client. It’s important to remember that the Dreamcast also had a keyboard peripheral.

  I need to check the timeline for when the web browser first became available vs. when the MIL-CD hack became known. My thinking is that there is no way that the web browser program didn’t have some security issues– buffer overflows and the like. It seems like this would have been a good method of breaking the security of the system.

  Ironically, I suddenly can think of a reason why one might want to use advanced reverse engineering tools on Dreamcast binaries, something I struggled with just a few paragraphs ago.

  Odds ‘n Ends
  It’s always fun to find plain text files among video game assets and speculating on the precise meaning… while also marveling how long people have been struggling to correctly spell “length”.

  Internationalization via plain text files.

  Another game (Slave Zero) saw fit to zip its assets. Maybe this was to save space in order to fit everything on the magazine sampler disc. Quizzically, this didn’t really save an appreciable amount of space.

  Finally, all the discs have an audio track 2 that advises that the disc must be played in a Dreamcast console. Not unusual. However, volume 4 also has a Japanese lady saying the same thing on track 4. This is odd because track 4 is one of the GD area audio tracks and is not accessible with normal CD hardware. Further, she identifies the disc as a “Windows CE disc”.

  The post Dreamcast Finds first appeared on Breaking Eggs And Making Omelettes.

• Understanding The Dreamcast GD-ROM Layout

  24 mars 2022, par Multimedia Mike — Sega Dreamcast

  I’m finally completing something I set out to comprehend over a decade ago. I wanted to understand how data is actually laid out on a Sega Dreamcast GD-ROM drive. I’m trying to remember why I even still care. There was something about how I wanted to make sure the contents of a set of Dreamcast demo discs was archived for study.

  
  
  

  I eventually figured it out. Read on, if you are interested in the technical details. Or, if you would like to examine the fruits of this effort, check out the Dreamcast demo discs that I took apart and uploaded to the Internet Archive.

  If you care to read some geeky technical details of some of the artifacts on these sampler discs, check out this followup post on Dreamcast Finds.

  Motivation
  Why do I still care about this? Well, see the original charter of this blog above. It’s mostly about studying multimedia formats, as well as the general operation of games and their non-multimedia data formats. It’s also something that has nagged at me ever since I extracted a bunch of Dreamcast discs years ago and tried to understand why the tracks were arranged the way they were, and how I could systematically split the files out of the filesystem. This turns out not to be as easy as it might sound, even if you can get past the obstacle of getting at the raw data.
  

  CD/CD-ROM Refresher
  As I laid out in my Grand Unified Theory of Compact Disc, every compact disc can be viewed conceptually as a string of sectors, where each sector is 2352 bytes long. The difference among the various CD types (audio CDs, various CD-ROM types) boils down to the format of contents of the 2352-byte sectors. For an audio CD, every sector’s 2352 bytes represents 1/75 of a second of CD-quality audio samples.

  Meanwhile, there are various sector layouts for different CD-ROM modes, useful for storing computer data. This post is most interested in “mode 1/form 1”, which uses 2048 of the 2352 bytes for data, while using the remaining bytes for error detection and correction codes. A filesystem (usually ISO-9660) is overlaid on these 2048-byte sectors in order to create data structures for organizing strings of sectors into files.

  A CD has between 1 and 99 tracks. A pure CD-ROM will have a single data track. Pure audio CDs tend to have numerous audio tracks, usually 1 per song. Mixed CDs are common. For software, this usually manifests as the first track being data and containing an ISO-9660 filesystem, followed by a series of audio tracks, sometimes for in-game music. For audio CDs, there is occasionally a data track at the end of the disc with some extra media types.

  GD-ROM Refresher
  The Dreamcast used optical discs called GD-ROMs, where the GD stands for “gigadisc”. These discs were designed to hold about 1 gigabyte of data, vs. the usual 650-700MB offered by standard CD solutions, while using the same laser unit as is used for CDs. I’m not sure how it achieved this exactly. I always assumed it was some sort of “double density” sector scheme. According to Wikipedia, the drive read the disc at a slower rate which allowed it to read more data (presumably the “pits” vs. “lands” which comprise the surface of an optical disc). This might be equivalent to my theory.

  The GD-ROM discs cannot be read in a standard optical drive. It is necessary to get custom software onto the Dreamcast which will ask the optical hardware to extract the sectors and exfiltrate them off of the unit somehow. There are numerous methods for this. Alternatively, just find rips that are increasingly plentiful around the internet. However, just because you might be able to find the data for a given disc does not mean that you can easily explore the contents.

  Typical Layout Patterns
  Going back to my study of the GD-ROM track layouts, 2 clear patterns emerge:

  All of the game data is packed into track 3:

  
  
  

  Track 3 has data, the last track has data, and the tracks in between contain standard CD audio:

  
  
  

  Also, the disc is always, always 100% utilized.

  Track 1 always contains an ISO-9660 filesystem and can be read by any standard CD-ROM drive. And it usually has nothing interesting. Track 3 also contains what appears to be an ISO-9660 filesystem. However, if you have a rip of the track and try to mount the image with standard tools, it will not work. In the second layout, the data follows no obvious format.

  Cracking The Filesystem Code
  I figured out quite a few years ago that in the case of the consolidated data track 3, that’s simply a standard ISO-9660 filesystem that would work fine with standard ISO-9660 reading software… if the data track were located beginning at sector 45000. The filesystem data structures contain references to absolute sector numbers. Thus, if it were possible to modify some ISO-9660 software to assume the first sector is 45000, it ought to have no trouble interpreting the data.

  
  
  

  How about the split data track format? Actually, it works the same way. If all the data were sitting on its original disc, track 3 would have data structures pointing to strings of contiguous sectors (extents) in the final track, and those are the files.

  To express more succinctly: track 3 contains the filesystem root structure and the directory structures, while the final track contains the actual file data. How is the filesystem always 100% full? Track 3 gets padded out with 0-sectors until the beginning of any audio sectors.

  
  
  

  Why Lay Things Out Like This?
  Why push the data as far out on the disc as possible? A reasonable explanation for this would be for read performance. Compact discs operate on Constant Linear Velocity (CLV), vs. Constant Angular Velocity (CAV). The implication of this is that data on the outside of the disc is read faster than data on the inside. I once profiled this characteristic in order to prove it to myself, using both PC CD drives as well as a Dreamcast. By pushing the data to the outer sectors, graphical data gets loaded into RAM faster, and full motion videos, which require a certain minimum bitrate for a good experience, have a better guarantee that playback will be smooth.

  Implications For Repacking
  Once people figured out how to boot burned CDs in the Dreamcast, they had a new problem: Squeeze as much as 1 gigabyte down to around 650 megabytes at the most. It looks like the most straightforward strategy was to simply rework the filesystem to remove the often enormous amount of empty space in track 3.

  My understanding is that another major strategy is to re-encode certain large assets. Full motion video (FMV) assets are a good target here since the prevailing FMV middleware format used on Sega Dreamcast games was Sofdec, which is basically just MPEG-1 video. There is ample opportunity to transcode these files to lower bitrate settings to squeeze some bits (and a lot of visual quality) out of them.

  Further, if you don’t really care about the audio tracks, you could just replace them with brief spurts of silence.

  Making A Tool
  So I could make a tool that would process these collections of files representing a disc. I could also adapt it for various forms that a Dreamcast rip might take (I have found at least 3 so far). I could eventually expand it to handle lots of other disc formats (you know, something like Aaru does these days). And that would have been my modus operandi perhaps 10 or more years ago. And of course, the ambitious tool would have never seen daylight as I got distracted by other ideas.

  I wanted to get a solution up and running as quickly as possible this time. Here was my initial brainstorm: assemble all the tracks into a single, large disc while pretending the audio tracks consist of 2048-byte sectors. In doing so, I ought to be able to use fuseiso to mount the giant image, with a modification to look for the starting sector at a somewhat nonstandard location.

  To achieve the first part I wrote a quick Python script that processed the contents of a GDI file, which was stored alongside the ISO (data) and RAW (audio) track track rips from when I extracted the disc. The GDI is a very matter-of-fact listing of the tracks and their properties, e.g.:

  5
  1 0 4 2048 track01.iso 0
  2 721 0 2352 track02.raw 0
  3 45000 4 2048 track03.iso 0
  4 338449 0 2352 track04.raw 0
  5 349096 4 2048 track05.iso 0
  

  track number / starting sector / track type (4=data, 0=audio) / bytes per sector / filename / ??

  The script skips the first 2 filenames, instead writing 45000 zero sectors in order to simulate the CD-compatible area. Then, for each file, if it’s an ISO, append the data to the final data file; if it’s audio, compute the number of sectors occupied, and then append that number of 2048-byte zero sectors to the final data file.

  Finally, to interpret the filesystem, I used an old tool that I’ve relied upon for a long time– fuseiso. This is a program that leverages Filesystem in Userspace (FUSE) to mount ISO-9660 filesystems as part of the local filesystem, without needing root privileges. The original source hasn’t been updated for 15 years, but I found a repo that attempts to modernize it slightly. I forked a version which fixes a few build issues.

  Anyway, I just had to update a table to ask it to start looking for the root ISO-9660 filesystem at a different location than normal. Suddenly, after so many years, I was able to freely browse a GD-ROM filesystem directly under Linux!

  Conclusion And Next Steps
  I had to hack the fuseiso3 tool a bit in order to make this work. I don’t think it’s especially valuable to make sure anyone can run with the same modifications since the tool assumes that a GD-ROM rip has been processed through the exact pipeline I described above.

  I have uploaded all of the North American Dreamcast demo discs to archive.org. See this post for a more granular breakdown of what this entails. In the course of this exercise, I also found some European demo discs that could use the same extraction.

  What else? Should I perform the same extraction experiment for all known Dreamcast games? Would anyone care? Maybe if there’s a demand for it.

  Here is a followup on the interesting and weird things I have found on these discs so far.

  The post Understanding The Dreamcast GD-ROM Layout first appeared on Breaking Eggs And Making Omelettes.

• ISO-9660 Compromise, Part 2 : Finding Root

  25 octobre 2021, par Multimedia Mike — General

  A long time ago, I dashed off a quick blog post with a curious finding after studying the ISO-9660 spec: The format stores multi-byte numbers in a format I termed “omni-endian”– the committee developing the format apparently couldn’t come to an agreement on this basic point regarding big- vs. little-endian encoding (I’m envisioning something along the lines of “tastes great! … less filling!” in the committee meetings).

  I recently discovered another bit of compromise in the ISO-9660 spec: It seems that there are 2 different methods for processing the directory structure. That means it’s incumbent upon ISO-9660 creation software to fill in the data structures to support both methods, because some ISO-reading programs out there rely on one set of data structures while the rest prefer to read the other set.

  Background

  As a refresher, the “ISO” extension of an ISO file refers to the ISO-9660 specification. This is a type of read-only filesystem (i.e, the filesystem is created once and never updated after initial creation) for the purpose of storing on a read-only medium, often an optical disc (CD-ROM, DVD-ROM). The level of nostalgic interest I display for the ISO-9660 filesystem reminds me of my computer science curriculum professors from the mid-90s reminiscing about ye olden days of punchcard programming, but such is my lot. I’m probably also alone in my frustration of seeing rips of, e.g., GameCube or Xbox or 3DO games being tagged with the extension .ISO since those systems use different read-only filesystems.

  I recently fell in with an odd bunch called the eXoDOS project and was trying to help fill in a few gaps. One request was a 1994 game called Power Drive for DOS.

  
  
  
  

  My usual CD-ROM ripping method (for the data track) is a simple ‘dd’ command from a Linux command line to copy the string of raw sectors. However, it turned out to be unusually difficult to open the resulting ISO. A few of the the options I know of worked but most didn’t. What’s the difference?

  Methods that work:

  • Mounting the file with the Linux iso9660 kernel module, i.e.,

    mount -t iso9660 /dev/optical-drive /mnt

    or

    mount -t iso9660 -o loop /path/to/Power-Drive.iso /mnt

  • Directory Opus
  • Windows 10 can read the filesystem when reading the physical disc
  • Windows 10 can burn the ISO image to a new CD (“right click” -> “Burn disc image”); this method does not modify any of the existing sectors but did append 149 additional empty sectors

  Methods that don’t work:

  • fuseiso
  • Dosbox
  • Winrar
  • 7zip
  • Daemon Tools
  • Imgburn
  • Internet Archive’s ISO lister (“View contents” on the ISO file)

  Understanding The Difference

  I think I might have a handle on why some tools are able to process this disc while most can’t. There appears to be 2 sets of data structures to describe the base of the filesystem: A root directory, and a path table. These both occur in the first substantive sector of the ISO-9660 filesystem, usually sector 16.

  A compact disc can be abstractly visualized as a long string of sectors, each one 2,352 bytes long. (See my Grand Unified Theory of Compact Disc post for deeper discussion.) A CD-ROM data track will contain 2048 bytes of data. Thus, sector 16 appears at 0x8000 of an ISO filesystem. I like the clarity of this description of the ISO-9660 spec. It shows that the path table is defined at byte 140 (little-endian; big comes later) and location of the root directory is at byte 158. Thus, these locations generally occur at 0x808c and 0x809e.

  
  
  Primary Volume Descriptor
  

  The path table is highlighted in green and the root directory record is highlighted in red. These absolute locations are specified in sectors. So the path table is located at sector 0x12 = offset 0x9000 in the image, while the root directory record is supposed to be at sector 0x62 = 0x31000. Checking into those sectors, it turns out that the path table is valid while the root directory record is invalid. Thus, any tool that relies on the path table will be successful in interpreting the disc, while tools that attempt to recursively traverse starting from root directory record are gonna have a bad time.

  Since I was able to view the filesystem with a few different tools, I know what the root directory contains. Searching for those filenames reveals that the root directory was supposed to point to the next sector, number 0x63. So this was a bizarre off-by-1 error on the part of the ISO creation tool. Maybe. I manually corrected 0x62 -> 0x63 and that fixed the interaction with fuseiso, but not with other tools. So there may have been some other errors. Note that a quick spot-check of another, functional ISO revealed that this root directory sector is supposed to be exact, not 1-indexed.

  Upon further inspection, I noticed that, while fuseiso appeared to work with that one patch, none of the files returned correct data, and none of the directories contained anything. That’s when I noticed that ALL of the sector locations described in the various directory and file records are off by 1!

  Further Investigation

  I have occasionally run across ISO images on the Internet Archive that return the error about not being able to read the contents when trying to “View contents” (error text: “failed to obtain file list from xyz.iso”, as seen with this ISO). Too bad I didn’t make a record of them because I would be interested to see if they have the same corruption.

  Eventually, I’ll probably be able to compile an archive of deviant ISO-9660 images. A few months ago, I was processing a large collection from IA and found a corrupted ISO which had a cycle, i.e., the subdirectory pointed to a parent directory, which caused various ISO tools to loop forever. Just one of those things that is “never supposed to happen”, so why write code to deal with it gracefully?

  See Also

  • The disc archived at The Internet Archive
  • MobyGames Entry
  • Wikipedia Entry

  The post ISO-9660 Compromise, Part 2: Finding Root first appeared on Breaking Eggs And Making Omelettes.

• Developing MobyCAIRO

  26 mai 2021, par Multimedia Mike — General

  I recently published a tool called MobyCAIRO. The ‘CAIRO’ part stands for Computer-Assisted Image ROtation, while the ‘Moby’ prefix refers to its role in helping process artifact image scans to submit to the MobyGames database. The tool is meant to provide an accelerated workflow for rotating and cropping image scans. It works on both Windows and Linux. Hopefully, it can solve similar workflow problems for other people.

  As of this writing, MobyCAIRO has not been tested on Mac OS X yet– I expect some issues there that should be easily solvable if someone cares to test it.

  The rest of this post describes my motivations and how I arrived at the solution.

  Background
  I have scanned well in excess of 2100 images for MobyGames and other purposes in the past 16 years or so. The workflow looks like this:

  
  

  

  Image workflow

  
  

  It should be noted that my original workflow featured me manually rotating the artifact on the scanner bed in order to ensure straightness, because I guess I thought that rotate functions in image editing programs constituted dark, unholy magic or something. So my workflow used to be even more arduous:

  
  

  

  I can’t believe I had the patience to do this for hundreds of scans

  
  

  Sometime last year, I was sitting down to perform some more scanning and found myself dreading the oncoming tedium of straightening and cropping the images. This prompted a pivotal question:

  
  Why can’t a computer do this for me?
  

  After all, I have always been a huge proponent of making computers handle the most tedious, repetitive, mind-numbing, and error-prone tasks. So I did some web searching to find if there were any solutions that dealt with this. I also consulted with some like-minded folks who have to cope with the same tedious workflow.

  I  came up empty-handed. So I endeavored to develop my own solution.

  Problem Statement and Prior Work
  
  I want to develop a workflow that can automatically rotate an image so that it is straight, and also find the most likely crop rectangle, uniformly whitening the area outside of the crop area (in the case of circles).

  As mentioned, I checked to see if any other programs can handle this, starting with my usual workhorse, Photoshop Elements. But I can’t expect the trimmed down version to do everything. I tried to find out if its big brother could handle the task, but couldn’t find a definitive answer on that. Nor could I find any other tools that seem to take an interest in optimizing this particular workflow.

  When I brought this up to some peers, I received some suggestions, including an idea that the venerable GIMP had a feature like this, but I could not find any evidence. Further, I would get responses of “Program XYZ can do image rotation and cropping.” I had to tamp down on the snark to avoid  saying “Wow! An image editor that can perform rotation AND cropping? What a game-changer!” Rotation and cropping features are table stakes for any halfway competent image editor for the last 25 or so years at least. I am hoping to find or create a program which can lend a bit of programmatic assistance to the task.

  Why can’t other programs handle this? The answer seems fairly obvious: Image editing tools are general tools and I want a highly customized workflow. It’s not reasonable to expect a turnkey solution to do this.

  Brainstorming An Approach
  I started with the happiest of happy cases— A disc that needed archiving (a marketing/press assets CD-ROM from a video game company, contents described here) which appeared to have some pretty clear straight lines:

  
  
  

  My idea was to try to find straight lines in the image and then rotate the image so that the image is parallel to the horizontal based on the longest single straight line detected.

  I just needed to figure out how to find a straight line inside of an image. Fortunately, I quickly learned that this is very much a solved problem thanks to something called the Hough transform. As a bonus, I read that this is also the tool I would want to use for finding circles, when I got to that part. The nice thing about knowing the formal algorithm to use is being able to find efficient, optimized libraries which already implement it.

  Early Prototype
  A little searching for how to perform a Hough transform in Python led me first to scikit. I was able to rapidly produce a prototype that did some basic image processing. However, running the Hough transform directly on the image and rotating according to the longest line segment discovered turned out not to yield expected results.

  
  
  

  It also took a very long time to chew on the 3300×3300 raw image– certainly longer than I care to wait for an accelerated workflow concept. The key, however, is that you are apparently not supposed to run the Hough transform on a raw image– you need to compute the edges first, and then attempt to determine which edges are ‘straight’. The recommended algorithm for this step is the Canny edge detector. After applying this, I get the expected rotation:

  
  
  

  The algorithm also completes in a few seconds. So this is a good early result and I was feeling pretty confident. But, again– happiest of happy cases. I should also mention at this point that I had originally envisioned a tool that I would simply run against a scanned image and it would automatically/magically make the image straight, followed by a perfect crop.

  Along came my MobyGames comrade Foxhack to disabuse me of the hope of ever developing a fully automated tool. Just try and find a usefully long straight line in this:

  
  

  Darn it, Foxhack…
  

  There are straight edges, to be sure. But my initial brainstorm of rotating according to the longest straight edge looks infeasible. Further, it’s at this point that we start brainstorming that perhaps we could match on ratings badges such as the standard ESRB badges omnipresent on U.S. video games. This gets into feature detection and complicates things.

  This Needs To Be Interactive
  At this point in the effort, I came to terms with the fact that the solution will need to have some element of interactivity. I will also need to get out of my safe Linux haven and figure out how to develop this on a Windows desktop, something I am not experienced with.

  I initially dreamed up an impressive beast of a program written in C++ that leverages Windows desktop GUI frameworks, OpenGL for display and real-time rotation, GPU acceleration for image analysis and processing tricks, and some novel input concepts. I thought GPU acceleration would be crucial since I have a fairly good GPU on my main Windows desktop and I hear that these things are pretty good at image processing.

  I created a list of prototyping tasks on a Trello board and made a decent amount of headway on prototyping all the various pieces that I would need to tie together in order to make this a reality. But it was ultimately slowgoing when you can only grab an hour or 2 here and there to try to get anything done.

  Settling On A Solution
  Recently, I was determined to get a set of old shareware discs archived. I ripped the data a year ago but I was blocked on the scanning task because I knew that would also involve tedious straightening and cropping. So I finally got all the scans done, which was reasonably quick. But I was determined to not manually post-process them.

  This was fairly recent, but I can’t quite recall how I managed to come across the OpenCV library and its Python bindings. OpenCV is an amazing library that provides a significant toolbox for performing image processing tasks. Not only that, it provides “just enough” UI primitives to be able to quickly create a basic GUI for your program, including image display via multiple windows, buttons, and keyboard/mouse input. Furthermore, OpenCV seems to be plenty fast enough to do everything I need in real time, just with (accelerated where appropriate) CPU processing.

  So I went to work porting the ideas from the simple standalone Python/scikit tool. I thought of a refinement to the straight line detector– instead of just finding the longest straight edge, it creates a histogram of 360 rotation angles, and builds a list of lines corresponding to each angle. Then it sorts the angles by cumulative line length and allows the user to iterate through this list, which will hopefully provide the most likely straightened angle up front. Further, the tool allows making fine adjustments by 1/10 of an angle via the keyboard, not the mouse. It does all this while highlighting in red the straight line segments that are parallel to the horizontal axis, per the current candidate angle.

  
  
  

  The tool draws a light-colored grid over the frame to aid the user in visually verifying the straightness of the image. Further, the program has a mode that allows the user to see the algorithm’s detected edges:

  
  
  

  For the cropping phase, the program uses the Hough circle transform in a similar manner, finding the most likely circles (if the image to be processed is supposed to be a circle) and allowing the user to cycle among them while making precise adjustments via the keyboard, again, rather than the mouse.

  
  
  

  Running the Hough circle transform is a significantly more intensive operation than the line transform. When I ran it on a full 3300×3300 image, it ran for a long time. I didn’t let it run longer than a minute before forcibly ending the program. Is this approach unworkable? Not quite– It turns out that the transform is just as effective when shrinking the image to 400×400, and completes in under 2 seconds on my Core i5 CPU.

  For rectangular cropping, I just settled on using OpenCV’s built-in region-of-interest (ROI) facility. I tried to intelligently find the best candidate rectangle and allow fine adjustments via the keyboard, but I wasn’t having much success, so I took a path of lesser resistance.

  Packaging and Residual Weirdness
  I realized that this tool would be more useful to a broader Windows-using base of digital preservationists if they didn’t have to install Python, establish a virtual environment, and install the prerequisite dependencies. Thus, I made the effort to figure out how to wrap the entire thing up into a monolithic Windows EXE binary. It is available from the project’s Github release page (another thing I figured out for the sake of this project!).

  The binary is pretty heavy, weighing in at a bit over 50 megabytes. You might advise using compression– it IS compressed! Before I figured out the --onefile command for pyinstaller.exe, the generated dist/ subdirectory was 150 MB. Among other things, there’s a 30 MB FORTRAN BLAS library packaged in!

  Conclusion and Future Directions
  Once I got it all working with a simple tkinter UI up front in order to select between circle and rectangle crop modes, I unleashed the tool on 60 or so scans in bulk, using the Windows forfiles command (another learning experience). I didn’t put a clock on the effort, but it felt faster. Of course, I was livid with proudness the whole time because I was using my own tool. I just wish I had thought of it sooner. But, really, with 2100+ scans under my belt, I’m just getting started– I literally have thousands more artifacts to scan for preservation.

  The tool isn’t perfect, of course. Just tonight, I threw another scan at MobyCAIRO. Just go ahead and try to find straight lines in this specimen:

  
  
  

  I eventually had to use the text left and right of center to line up against the grid with the manual keyboard adjustments. Still, I’m impressed by how these computer vision algorithms can see patterns I can’t, highlighting lines I never would have guessed at.

  I’m eager to play with OpenCV some more, particularly the video processing functions, perhaps even some GPU-accelerated versions.

  The post Developing MobyCAIRO first appeared on Breaking Eggs And Making Omelettes.