We all know that speakers are microphones and microphones are speakers, right? If not, take a moment to plug your headphones into a microphone jack and yell into them. It’s not exactly hi-fi, but it works.
[Huan Truong] was given a WiFi router and thought he’d improve it by installing a free firmware on it. Unfortunately, the router in question is a bit old, and wasn’t ever popular to begin with, which meant that it was unsupported by the usual open firmware suspects. The problem was that it only had a 4 MB flash to boot off of, but [Huan] was determined to make it work. (Spoiler: he did it, and documented it fully.)
The flash workaround consisted basically of repartitioning the space, and then telling u-boot where to find everything. On a router like the WNR2000 that [Huan] had, the flash is memory-mapped, which meant adding an offset to the flash start (0xbf000000 instead of 0x00000000) and remembering to do this consistently so that he doesn’t overwrite things like the MAC address.
[Huan] went for the LEDE fork of OpenWRT, and rebuilt it from source because he needed a small version to fit inside his limited flash. With this task completed, it worked. All done? Nope, [Huan] then submitted a pull request to LEDE, and now you can enjoy the fruits of his labor without replicating it. But if you’ve got another low-flash, obscure router, you’ve got a head start in getting LEDE up and running on it.
Routers are perhaps the most-hacked device that we see here, and they can be made pretty darn useful with the right firmware. Sometimes getting a custom firmware running is relatively easy, as it was here, and sometimes it requires some deep reverse engineering. But it’s good to keep up your router-hacking chops, because they may not always be as open as they are now.
Wouldn’t it be great if there were just one standard for attaching to, programming, and debugging hardware? If you could just plug in and everything would just work? Dream on, dreamer! But of course we hobbyists aren’t the only people to suffer from multiple standards. Industry has the same problems, writ large. In response to the proliferation of smart devices — microcontrollers, sensors, and their friends — on any given PCB makes it difficult to test them all, much less their function as a system.
The Joint Test Action Group (JTAG) got together in the mid-80s to make automated testing of circuit boards a standardized process. A JTAG port can be found on almost any piece of consumer electronics with enough brains to warrant it, and it’s also a tremendously useful entry point for debugging your own work and hacking into other’s. You’re going to need to use JTAG someday.
Implemented right, it’s a very cool system that lets you test any compliant IC on the board all from a single connector. It’s mostly used by hackers for its ability to run and halt individual processors, and put them in debugging modes, inspecting their memory states, etc. Essentially every microcontroller responds to JTAG commands, and it’s an incredibly widespread and powerful standard. A victory for rationality and standardization!
The connector pinout was, of course, left up to the manufacturer. The horror!
In principle, JTAG uses five signal lines. They form a chain starting at the debugger, where one device’s output is the next device’s input, until the result is returned back to the debugger.
Test Data In (TDI) is the input from the debugger
Test Data Out (TDO) is the return end of the chain
Test Clock (TCK) clocks this data along synchronously, similarly to SPI
Test Mode Select (TMS) lets the devices know that they’re being debugged — it’s a global chip select
Test Reset (TRST) is an optional signal that resets all devices in the chain
If the headline makes today’s hack sound like it was easy, rest assured that it wasn’t. But if you’re interested in embedded device hacking, read on.
[Andres] wanted to install a custom OS firmware on a cheap home router, so he bought a router known to be reflashable only to find that the newer version of the firmware made that difficult. We’ve all been there. But instead of throwing the device in the closet, [Andres] beat it into submission, discovering a bug in the firmware, exploiting it, and writing it up for the manufacturer. (And just as we’re going to press: posting the code for the downgrade exploit here.)
This is not a weekend hack — this took a professional many hours of serious labor. But it was made a lot easier because TP-Link left a debugging protocol active, listening on the LAN interface, and not requiring authentication. [Andres] found most of the information he needed in patents, and soon had debugging insight into the running device.
We’re not sure why [lujji] would want to hack ST’s ST-Link programmer firmware, but it’s definitely cool that he did, and his writeup is a great primer in hacking embedded devices in two parts: first he unpacks and decrypts the factory firmware and verifies that he can then upload his own encrypted firmware through the bootloader, and then he dumps the bootloader, figures out where it’s locking the firmware image, and sidesteps the protection.
[lujji]’s project was greatly helped out by having the firmware’s encryption keys from previous work by [Taylor Killian]. Once able to run his own code on an intact device, [lujji] wrote a quick routine that dumped the entire flash ROM contents out over the serial port. This gave him the bootloader binary, the missing piece in the two-part puzzle.
If you’ve ever broken copy protection of the mid-1990’s, you won’t be surprised what happened next. [lujji] located the routine where the bootloader adds in the read protection, and NOPped it out. After uploading firmware with this altered bootloader, [lujji] found that it wasn’t read-protected anymore. Game over!
We glossed over a couple useful tips and tricks along the way, so if you’re into reversing firmware, give [lujji]’s blog a look. If you just want a nice ARM programmer with UART capabilities, however, there’s no reason to go to these extremes. The Black Magic Probe project gives you equal functionality and it’s open source. Or given that the official ST-Link programmers are given away nearly free with every Nucleo board, just buying one is clearly the path of least resistance. But a nice hack like this is its own reward for those who want to take that path. Thanks, [lujji] for writing it up.
Due largely to the overwhelming dominance of mobile phones, payphones are a sometimes overlooked relic from the 90’s and earlier eras. While seldom seen out in the wild these days, they can however still be acquired for a moderate fee — how many of you knew that? Setting out to prove the lasting usefulness of the payphone, Instructables user [Fuzzy-Wobble] has dialed the retro spirit way past eleven to his ’90 from the ’90s’ payphone boombox.
Conspicuously mounted in the corner of his office, a rangefinder sets the phone to ringing when somebody walks by — a fantastic trap for luring the curious into a nostalgia trip. Anyone who picks up will be prompted to punch in a code from the attached mini-phone book and those who do will be treated to one of ninety hits from — well — the 1990’s. All of the songs have been specifically downgraded to 128kbps for that authentic 90’s sound — complete with audio artifacts. There’s even a little easter egg wherein hitting the coin-return lever triggers the payphone to shout “Get a job!”
We love squeezing every last bit of silicon goodness out of a tiny chip, or at least we delight in seeing it done. Today’s analog/digital hack is one of the sweetest we’ve seen in a while. And it’s also a little bit of a puzzle, so don’t scroll down to the answer until you’ve given the schematic a good think-over.