this post was submitted on 17 Feb 2025
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Celebrating/talking about repairing stuff, the right to repair stuff, and the intersection of tech and solarpunk ideals.
What does it mean to use what we have, including technology, to try to build a better, more environmentally just world?
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The MCU is an ATmega32L, which seems to be well documented. I was able to fetch a 300+ page document and a 12 page overview of the specs.
That is a microcontroller. I don't have a lot of experience with hacking around with commercial products like this. It is not capable of running something like embedded Linux or a standard real time operating system. It could in theory be running Arduino, but probably not with the ISP connector. It was likely developed with the Microchip toolchain for ISP support. In this instance, the serial port is likely used for feedback only and not some interactive like interface. There may be some functionality programmed or the port may have been disabled after it was used in the jig that did the initial programming and tests.
Most of the info you will find about using UART to hack around is related to embedded Linux where UART is a full terminal interface. Devices capable of running embedded Linux are the next level above something like an ESP32 microcontroller.
The datasheet for the ATMega32L is not really relevant to you unless you want to rebuild the entire software stack from scratch. Reverse engineering and rebuilding is a major project even for a pro dev.
The manufacturer as you perceive a brand is likely just a logistics and label maker with little to no relevance to your actual device. The components PR entire machine were likely out sourced and contract manufactured. In the world of contract manufactured goods, the software is usually just a checklist of features. As soon as the checklist is complete and verified, the dev gets paid and is never seen again. If the company wants something more or something changed it will cost a fortune for the old dev to return or a new one to read-in to the code and make changes or just start over. This kind of thing might happen when versioning is required because some part is not available or something like that during production runs.
Each run is like a one time thing. Some capital is put together and parts are sourced, then the contractor makes like 5k of the thing over the course of 2 weeks. These go in shipping containers around the world with whatever brand stickers applied. When each run is done, the software and any unique tooling are consumables to the whole affair and not something anyone cares about or keeps like a real asset of value. It is probably archived in several private databases on various employee's computers, but these are not connected in any way to aid or support your needs. It is in the best interest of the company to never give out this info.
Also getting the whole microcontroller toolchain working is a major pain in the ass. That large datasheet is because a microcontroller is a whole computer all integrated into a single chip. It is just a very simple type of computer. You need to understand all of the peripheral parts of computing to really make sense of it in practice. It is not just a microprocessor.
Embedded Linux means that there is a kernel and user space abstraction layer that makes the unique hardware irrelevant and abstracted away. Without this abstraction layer, you need to know and understand that actual hardware assembly, or use a language like C and a compiler for the actual hardware. This is the level you are facing.
I don’t intend to modify the program. I am just looking to reset the state of the software to get it out of the fault state.
Normally that can be done by using the buttons on the PCB to enter a secret combination code to:
When the software detects a fault (such as a broken pump), it saves the error code. Then if you fix the pump, the software doesn’t know the pump has been fixed. So the board has to be reset to clear the error code.
The button sequence codes are secret and known only to the manufacturer. They are very protectionist. In Europe, law requires them to make the codes available to other 3rd party technicians -- but only in the 1st ten years and they can also charge a fee. Consumers get no access under any circumstances.
My thought was theoretically a pro independent repair service would not want to pay every manufacturer for the secret info for every model they repair -- so perhaps they would attach to the USART serial port and have a way to see errors and reset the board. But if it’s as you say, then the USART is disabled and useless to repairers. Which means I’m stuffed because I cannot buy a replacement card for my machine.
If the serial port is not disabled, you conjecture that it is likely a read-only non-interactive mechanism. That still may be useful. I was able to find the secret button combination that is likely giving me an error code which I can guess the meaning of based on leaked docs for other models, but I’m not satisfied with that. I would be useful if I could get more verbose or supplemental info about the error state.
There is some chatter about GE washing machines (not what I have) include an rj-45 port and that they released some kind of open source thing called the green bean which adapts USB to serial. On the one hand, it suggests that not all manufacturers intend to prevent communication with the PCB. OTOH, this actually seems to not be for service use but for sending notifications to the user.
In the last 10 years it has become common for devs to disable and remove or encrypt to prevent reverse engineering and repairs. If the device is older, the debug info from UART is likely still present. How useful that information is may be dubious.
Most of what you are saying about functionality is not in line with how a microcontroller works. The microcontroller is not sophisticated like a real computer. It is like a very simple state machine running on the device. Basically it is like a single long script that is not running on any kind of abstraction layer. When the device is turned on, there is the script. The script is not executed by some operating system or any other complication. The entire software stack is the script. Only, the script is actual hardware registers and flags and operation codes.
There is a tiny amount of RAM that actually runs the script, like 16kb. There is the programmed memory, like 32kb. Then there is a tiny amount of electrically erasable and reprogrammable memory, like 4kb. The eeprom is the only section of memory that a microcontroller can access to write persistent data, meaning something that will still be present when power is cycled.
I doubt many people use eeprom to save any kind of error. This is more like where a serial number might be saved, or more likely the calibration values for some internal control algorithm. It is not anywhere near large enough to save something significant like the script.
It is far more likely that the script is just a state machine and is reaching an error state because of some missing or bad signal that it needs to continue running the script. This is likely your problem and the issue is like 99% likely to be hardware and not the microcontroller.
Resetting such a device is just an interrupt signal that restarts the script. There is nothing dynamic about this.
From the perspective of the original dev, the ISP programming interface has the functionality of brute forcing running code to step through each machine instruction and halt further execution while monitoring or changing any value present in any register of the internal microprocessor. This is super powerful but requires a pricy setup from the manufacturer in most cases, and a thorough understanding of the internals of a microprocessor's registers, op codes, memory addressing, interrupts, clocks, and the ALU (arithmetic logic unit).
In this type of device, text strings are far too expensive to have much, if any, value. Any such debug info is likely to be very terse. Text strings take an enormous amount of memory space to encode, so in general, these are not used very much. A microcontroller is a far simpler device than this. It is a computer in the sense of a device that can do Input/Outputs and run a control algorithm like a temperature controller with a PID loop.