Category: Daily Events

Discovering little worlds

Like so many other people during the COVID lockdown, I’ve been looking for additional hobbies that could be done from home, which would occupy my time and help keep my mind off the collapse of civilization as we know it, and maybe even ground my thoughts and keep them away from hyperbole and catastrophizing.

While cleaning and organizing my basement I came across this small USB device. It’s barely larger than a flash drive, but it’s no flash drive at all – it’s a software-defined radio (SDR), namely an RTL-SDR V3 dongle.

I don’t even recall how this device ended up in my possession;  I think it was probably from one of my previous jobs:  they were throwing away a bunch of equipment that was no longer useful, and allowed me to keep some of the items.  Regardless, I had never actually used the SDR, and hadn’t really thought about what the SDR would be useful for.  I had a vague understanding that the SDR can let me tune in to any random radio frequency, but how interesting can that be?  Well, it turns out that playing around with this device led me into a rabbit hole of epic proportions.

Once I found the right software to work with the SDR device (SDRSharp for Windows, and CubicSDR for Mac), I was up and running.  The first rather trivial thing to do was to tune in to the local FM radio stations. Here they are, as viewed through a spectrogram:

FM radio

But that’s kind of boring. I wonder what lies outside of the FM radio band? Well, the next obvious destination is the local police frequencies, which are around 460 MHz to 490 MHz in my area. These are narrow-band FM (NFM) stations, so we adjust our software settings accordingly. In mere moments, I’m listening to police dispatchers communicating with units and telling them about robberies, car accidents, and the like:

And of course there are a few local HAM radio repeaters nearby, which tells me that the HAM community is very much alive and well.  Since I can’t transmit anything using my tiny SDR device, I can only listen in on the HAM conversations, but that’s okay since the conversation wasn’t particularly scintillating anyway, and I’m not sure that getting into the little world of HAM radio is really my goal here. As much as I salute the enthusiasts who keep HAM radio going, they can party on without me.

Mind you, all of this was using the cheap tiny antenna that came with the SDR itself.  But then I discovered that the SDR can be used for something else entirely: receiving signals from satellites!

Arguably the easiest satellites to pick up signals are the NOAA 15/18/19 satellites, which are weather satellites that transmit images of cloud cover over the ground. By “easiest” I mean requiring the least amount of additional equipment:  it only requires a rabbit-ear (V-dipole) antenna connected to your SDR, and a cloud-free day to get a good signal. Here is the signal at 137.9 MHz, and the resulting image, which is produced by special software that demodulates the “audio” data that was recorded:

The downside is that these satellites are in a sun-synchronous orbit, and will only pass by your location for ~15-minute intervals at the most, and can only be caught at very early or late hours of the day. The other downside is that the NOAA satellites are aging, and will probably be decommissioned in the coming years. And anyway, the images they transmit are not the highest quality. Time to step it up to the next level, namely the GOES satellites!

The GOES-16 satellite is a newer weather satellite that is geostationary, and is positioned permanently above the Americas. In fact its longitude is almost exactly over the East coast, which is perfect for my purposes, and its inclination from my location is about 45 degrees (because it orbits around the equator, as all geostationary satellites must do).

But because it’s geostationary it’s also much farther away, and therefore its signal is much weaker, and requires additional equipment:

The setup consists of an old WiFi grid antenna, which feeds into a SAW filter and amplifier, which then feeds into the SDR that’s now connected to a Raspberry Pi (the total cost was about $100).  The Raspberry Pi is running a package called goestools which demodulates the signal from the satellite in real time, and translates the signal into images. The satellite transmits images of Earth in many different spectral bands, ranging from visible light to deep infrared.

And so, the final little world I discovered on this adventure is this one:

The full resolution of these images is 10K, which is mind-blowing, and my next step is to create animations from these images, which are sent by the satellite every 15 minutes.

I think I’ll leave this antenna setup as a permanent installation in my house, so that I can grab these signals anytime I like. Even though this imagery is available on the web if you know where to look, there is something profoundly awesome in knowing that you personally can receive selfies of our world, from 35,000 kilometers away, using about $100 worth of equipment. It’s been a very satisfying few weeks, in spite of everything else that’s happening this year.

Thoughts on the new Star Trek

I watched Star Trek: Picard recently, and… I am sad.

Gene Roddenberry had a vision: a future which is truly post-racial, post-war, post-poverty, etc. It’s a world for us to strive towards, to admire, to want to live in.  But the world of Star Trek: Picard seems to have all the same problems we have in the 21st century.  The Federation is a systemically racist organization that refuses to help an enemy in a time of desperate need. There is deep wealth inequality between different classes of people on Earth. People treat sentient androids like property. And all of “space” is a hostile battleground where one dares not venture without being armed to the teeth.

That’s not a world I look forward to living in, and it would be depressing to me if this is how humanity “turns out” in three hundred years.

Aside from pontificating about today’s political issues, the show’s plot is completely incoherent, and the writing is so lazy and unfocused. Remember Picard’s caretakers at his château who were former Tal Shiar? Those were some interesting characters, but will we ever see them again? Was there any point in having the Borg involved in the story at all? Does the Romulan Samurai kid (bet you can’t think of his name!) have any purpose than to chop people’s heads off? Will Agnes’s murder of Bruce Maddox be swept under the rug? Will the fact that Picard is now a synthetic golem ever be mentioned again?

One perfect example of lazy writing is embodied in the hand-held purple repair device that the Androids conveniently give to Captain Rios. This device basically grants wishes: you can wish it to repair your broken warp core! Or you can wish it to create a mirage of a hundred starships, complete with warp signatures that can fool Romulan sensors! What luck!

And think about how Old Trek and New Trek are different in terms of fandom. There are fans who transform their basement to look like the bridge of the Enterprise. There are fans who program their desktop computer to look like an LCARS interface. And of course there are countless fans who attend conventions dressed up like characters from the Original Series and Next Generation. But will there be any fans who’ll want to recreate the bridge of Captain Rios’s ship (bet you don’t know what it’s called)? Will there be any fans who will admire or want to emulate any of these new characters?

Is it possible anymore to have a show where the whole universe isn’t about to blow up all the time? Can we just have a show where the Enterprise goes to a planet, and Picard negotiates a peace accord, while Data and Geordi get into a wacky holodeck adventure?  I ask for so precious little!

The problem of recovering data from SSD drives

One frequent question I receive from users of DiskDigger is: Why does it seem to be unable to recover data from my internal SSD drive? And since SSDs have become nearly ubiquitous in laptops and desktops, this question is becoming more and more common.

The short answer: It is generally not possible to recover deleted data from internal SSD drives, because they are very likely using the TRIM function.

How do I know if TRIM is enabled?

It probably is. If you have an SSD drive that is internal to your computer (NVMe drive, SATA drive, etc), and you’re using a modern operating system (Windows 7 and newer, macOS, etc), then it’s likely that TRIM will be enabled by default, because it’s highly beneficial to the performance of your SSD drive.

Why?

SSD (flash memory) drives work fundamentally differently from older magnetic (spinning disk) hard drives.

With both types of drives, when data is deleted, the physical blocks that were occupied by the data are marked as “available”, and become ready to be overwritten by new data.

With a magnetic spinning hard drive, an available block can be overwritten regardless of what data was in that block previously; the old data gets overwritten directly. However, the same is not true for flash memory: a flash memory block must be erased explicitly before new data is written to it. And this erase operation is relatively expensive (i.e. slow). If an SSD drive was to erase memory blocks “on demand”, i.e. only when a new file is being written, it would slow down the write performance of the drive significantly.

Therefore, an SSD drive will erase unused memory blocks preemptively, so that the memory will be pre-erased when a new file needs to be written to it. Since the drive has no knowledge of what filesystem exists on it, the drive relies on the operating system to inform it about which memory blocks are no longer used. This is done using the TRIM command: When the operating system deletes a file, in addition to updating the necessary filesystem structures, it also sends a TRIM command to the drive, indicating that the memory blocks occupied by the deleted file can now be considered “stale”, and queued up for erasing.

The SSD drive erases TRIMmed blocks in the background while the drive is idle, transparently to other operations. In effect this means that for any file that’s deleted from an SSD drive, once the drive purges those stale blocks, the actual contents of the file will be wiped permanently from the drive, and will no longer be recoverable.

The above is a slight simplification, since SSD drives also perform wear-leveling which uses rather complex logic involving copying and remapping logical addresses to different physical memory pages, but the general point stands.

Exceptions

There are a few cases when deleted data may be recoverable from an SSD drive:

  • If TRIM happens to be disabled for some reason. As mentioned above, the TRIM feature is something that is enabled at the level of the operating system. It is usually enabled by default for performance reasons. Nevertheless, most operating systems will let you check whether or not TRIM is enabled, and optionally disable it. For example, in Windows you can run the command fsutil behavior query disabledeletenotify to see if TRIM is currently enabled.
  • If you’re using an external SSD drive connected over USB. Support for issuing the TRIM command over a USB connection is relatively new, and is not yet supported by all USB controllers and operating systems. If you deleted files from an external SSD drive that’s connected to a USB port, there’s a fair chance that the data might be recoverable.
  • If you attempt to recover the files immediately after they’re deleted, and the drive provides the contents of stale blocks (which is rare). As mentioned above, the TRIM command puts the deleted memory blocks in a queue of stale blocks, so it’s possible that the SSD drive won’t actually erase them for a short while. The timing of when exactly the TRIMmed blocks are erased is entirely up to the drive itself, and differs by manufacturer. If you search the drive for deleted data sufficiently soon after it’s deleted, and the drive doesn’t return null data for stale blocks, it may still be possible to recover it.
  • Due to the way that SSD drives perform wear-leveling, it may be possible for stale blocks to get reallocated and copied to different physical positions in the drive, leaving behind the original data in their old locations. Unfortunately this kind of data is generally not accessible using any software tools, including DiskDigger, and can be accessed only by disassembling the drive and reading the physical flash memory chip directly, which is a very expensive procedure done by enterprise-level data recovery labs.

Summary

Despite the above challenges, there’s no harm in trying to use DiskDigger to recover files from your SSD drive, and in certain cases it will be successful. However, if you’ve deleted files from an internal SSD drive, the overall prognosis for recovering them is unfortunately not good.

Reverse engineering a 25-year-old Visual Basic app

Following up from last week’s misadventures with the Avant Stellar keyboard (trying and failing to extract macro information from the keyboard’s internal memory), there was another glimmer of hope:  my friend found a backup file that possibly contains all the macros that were saved to the keyboard.  If I could just reverse-engineer this backup, we could extract the macros directly from the file.  It is a 2 KB file with a .KBD extension, unrecognizable as any binary format I’ve seen to date. Here is a partial hex dump of the file:

It’s pretty clear that the file contains a key mapping, as evidenced by the list of incrementing 32-bit numbers at the beginning, up to offset 0x210.  There are roughly 120 increasing numbers, which is roughly the number of keys on the keyboard, so we can safely assume that this is the key mapping.  After the key mapping, I presume, comes the macro information, and this is where things get tricky, since there’s virtually no way to tell how the macros are encoded in the file. The data simply looks too general to make sense of.

An obvious possibility would be to “load” the backup file into the Avant software tool that came with the keyboard, and visually inspect the macro(s) assigned to each key.  But no matter what I tried, the software would not load the file.  Or rather, it loaded the key mapping, but not the macros.  Time to think about the nuclear option: disassemble the Avant software and see how it’s actually processing the backup file.

Looking at the folder contents of the Avant software tool, I immediately notice a dead giveaway: VBRUN300.DLL, which means this tool was written in Visual Basic 3.0.  This makes our job much easier, because there are actually ready-made tools for decompiling Visual Basic executables. (If you recall, Visual Basic compiles executables into p-code instead of native machine code, which makes them much more straightforward to decompile.)  All of this took me quite a while to remember, because I hadn’t used these tools since my early, early hacking days, and it took a little while longer to find them in my archives!  The go-to utility for performing this task was literally called VB3 Decompiler, and the way to find this tool on the web today is… outside the scope of this post.

The decompilation basically results in several Visual Basic source files, in which the original function names are intact, but the local and global variables are changed to generic identifiers, since those names are not stored in the compiled code. It takes a little bit of further massaging to get these files to actually build within Visual Basic, but after that, it’s almost as if you have the original source code of the program at your fingertips.

There was one other minor hurdle because the Avant software uses custom UI components (.VBX files) that don’t allow themselves to be used in Design mode (as part of a copy-protection or licensing mechanism), but this is bypassable using another utility in the decompiler suite that “fools” Visual Basic into loading the components anyway.

With the source code buildable and debuggable, we can now easily run the program and load the .KBD backup file, and trace through where it processes the data in the file:

Even though the variable names aren’t very descriptive in the above screenshot, it’s easy enough to spot the loop that deserializes the keyboard macros, and how each macro is composed.  Not only that, but we can determine what was preventing it from displaying the macros in the first place – it turned out that it expects the keyboard to be physically connected while running, and while I’m pretty sure that we tried loading the backup with the keyboard attached, it wasn’t working anyway, probably because the keyboard is malfunctioning and no longer able to communicate properly.  But at last, with this requirement bypassed, the macros that were loaded from the backup file finally reveal themselves:

Homeowner’s log, May 2020

Symptom: The previous owners of the house left behind a nice gasoline-powered chainsaw, which I was looking forward to using to cut up some fallen tree branches. Unfortunately the chainsaw refused to start up. Right away I noticed that the primer bulb was cracking, and virtually disintegrated when I continued to press it.

Solution: I took apart the chainsaw and realized that not only had the primer bulb disintegrated, but also the fuel lines had crumbled, so there was no way for fuel to get from the tank to the engine. I’m guessing this might have been because the chainsaw was left in the garage in the wintertime, possibly for multiple winters. When looking for replacement parts on eBay, I noticed there were pre-made kits for sale that contained a primer bulb, a generous length of tubing to serve as a fuel line, as well as new filters for oil and fuel. Apparently these are all very common points of failure. This kit cost less than $10, and installing the new bits took about two hours. The chainsaw now runs as smooth as butter, and I’ll try to give it better maintenance going forward.