If you wanted to extract the firmware from a mystery device, you might pull the flash chip out of it and toss it into a reader. But if you only had one chance to get it right and couldn’t risk damaging the device in the process, physically removing the chip may seem much less attractive. Reading the chip in-circuit failed — because of course it did — so what does that leave?
Well, if you follow the example of [Matthew “wrongbaud” Alt], the next tool you reach for might be a logic analyzer. In a recent write-up, [wrongbaud] explains the process of identifying, capturing, and ultimately decoding the SPI read operations used to load the firmware from a common W25Q-series flash chip at boot time. He notes it’s not a perfect solution, as in the end you’ll only be able to sniff out what the CPU actually reads, not necessarily the entire contents of the chip, but it’s a big step in the right direction if you’re reverse engineering something in the dark.
For his own reasons, [Jose Luis Monteiro] (aka [emsyscode]) decided he needed to drive the LCD on a Sony CDX-A250 car stereo’s front panel using an Arduino. There’s probably a sweet project in the works, or perhaps he just wanted to see if it could be done. Either way, more power to [Jose], because he totally pulled it off and put the results up on GitHub for all to enjoy. There’s also a project video showing how he did the reverse-engineering, which you can see below.
The driver for this diminutive LCD is a chip obviously labeled LC75826W, and that’s what the Arduino ends up talking to. Thankfully, there was a datasheet available for that part, which gave [Jose] a great starting point for figuring out how to use it. While [Jose] is working with the LC75826W driver, he’s quite explicit in his GitHub repo that this repository is not a driver library for that chip. The code only targets the specific LCD on the CDX-A250 head unit. Still, if you’ve got a different oddball LCD that uses this driver, [Jose]’s code is a great place to start, and since it’s under an MIT license, you can fork to your heart’s content.
Kudos to Sony for not obfuscating the part or using a chip-on-board black blob — you can reverse-engineer an LCD driven by one of those, but it’s a lot more work. If you’re wondering how and why those black blobs come to be, we’ve got you covered.
It is a classic Hackaday situation. You have an Egret GT E-scooter. It has a screen that shows the usual dash stats, but that led to an annoyance. You could accidentally enter firmware update mode and, from there, enter operational mode without the security PIN. [Ben] couldn’t let that stand, so he reverse-engineered the protocol and rewrote the firmware in Rust. As he put it, “… because I have to break… everything I own…” We get it.
The mobile app was useful for some basic info, since sniffing Bluetooth is fairly easy and analyzing mobile code is, more or less, straightforward. Analysis revealed some data that doesn’t show on the display and that several things are sent back to home base tagged with the scooter’s unique ID — another reason to gut the existing firmware.
During his continuing analysis of the architecture and microcode of Intel’s highly influential 8087 floating point unit (FPU) co-processor, [Ken Shirriff] has now arrived at the point where he can put together how the 8087’s microcode implements various x87 instructions. One of these, the FSCALE instruction turned out to be far more complicated than assumed, with one might assume to be a straightforward powers-of-two scaling turning out to entail over 140 micro-instructions and three levels of sub-routine calls just to handle all cases.
The annotated die shot in the heading image shows the functional blocks that are used by this one x87 instruction, to give some kind of idea of what amount of hardware even ‘just’ scaling a floating point number involves.
Much like with the x86’s CISC-style ISA, these 8087 instructions break down into individual steps that involve everything from loading values into registers, performing operations, checking for and handling error conditions as well as stack management. As can be seen in [Ken]’s breakdown of the FSCALE implementation in the 8087 it’s all very logical, taking a high-level instruction and doing all that’s needed for a robust implementation, without bothering the developer with the details.
Of note is that the 8087’s implementations led to the IEEE 754 floating point standard, providing what definitely at the time was one of the most mathematically accurate FPUs that somehow still was financially responsible enough to make it into a relatively affordable PC.
The Philips PM5139 is not famous. It won no great victories on the battlefield, nor was instrumental in changing the political landscape. It was just a useful function generator that you might find on a workbench somewhere, doing its job quietly and relatively accurately. [doctormord] has been doing the work to reverse engineer this humble piece of hardware.
The PM5139 is poorly documented; the only existing service manual out there is for the PM5138A, a less-capable sister model. Hence, there was some value in reverse engineering the device to understand it better. Work started with two EPROM dumps capturing what Philips put in the box all the way back in the early 1990s. From there, the code was examined and tinkered with until [doctormord] felt confident to modify it and improve upon what was already there. This was achieved with the aid of an 8051 emulator that could run the code to make it obvious what was going on. The result was a custom “V2.0” firmware that adds six arbitrary waveforms to the function generator and the ability to play simple music, amongst other tweaks.
The NEC V20 is an Intel 8088-compatible processor that features the same use of microcode, though with its own characteristics. This makes it important to use this same microcode if your goal is to create a cycle-accurate emulator of this processor, as [GloriousCow]’s goal is. Cue decoding the microcode ROM in a die shot of this CPU, in order to create a usable ROM image.
As with any fabricated ROM you can technically do it by hand, the ROM section in the die shot contained 29,928 bits which even at a pretty zippy pace would take up a considerable amount of time to parse. Here you can divide-and-conquer by handing parts of the ROM off to good friends, or you can use automation and some machine vision and theoretically get an answer as soon as you have finished writing and testing the tool.
Close-up of some of the microcode bits.
Although [Travis Goodspeed]’s MaskRomTool exists exactly to automate bit detection, it was found that there wasn’t enough contrast in the die shot for it to work reliably. What it did provide were the locations of the bits and from it 42×42 pixel PNG files of each bit.
Next a convolutional neural network (CNN) was trained to determine the difference between a 0 and 1 bit. This still took the manual classifying of 1,000 images, but seemed to work fairly well. Although some bits were marked as ambiguous, it was easy enough to use Mark 1 eyeballs to run a classification on these handful of images than to tweak the CNN model.
With this microcode in hand it was then possible to match it against the V20’s internal architecture to fully determine what each part does. Although not quite finished yet, there’s a GitHub repository containing the progress so far.
The V20’s microcode has been the focal point of much legal fighting back when NEC and Intel were still duking it out in how far one could make a CPU compatible with that of a competitor.
If you are a regular reader, then the odds are you have taken apart an electronic gadget, either for a fix, or simply because your curiosity got the better of you. Once inside, it’s all but impossible to help yourself from doing at least a little reverse engineering. That’s what happened when [PRBS23] took a look inside a MasterBuilt Gravity 800 Grill for a simple wire fix. But one thing led to the next, and now open source firmware for the grill is freely available!
The thermistor along with the physical inputs are connected to a 16 pin chip, interfacing with the MCU over a 9600 baud UART connection. [PRBS23] cannot determine an ADC chip meeting these specifications, so the most likely answer is a cheap MCU programmed to act as a simple analog fronted.
The neatly labeled programming header is used to quite easily dump the firmware with the espflash utility. Analyzing this dump reveals a rather strange ADC correction function used by the original firmware. The necessity and overall utility of this function remains unclear, does corrects a maximum of around 40 degrees Fahrenheit.
Most of the other features ended up being at least somewhat easier. The CS1621 segmented display driver is reasonably well documented with datasheets making its implementation far easier. Likewise, the other odds and ends were implemented in a far more normal manner compared to the thermistors.
