Thu Sep 12 00:21:07 UTC 2024: ## Linux on a Business Card: A Tiny Computer, a Huge Feat

**A hobbyist engineer has created a working Linux computer that can fit on a business card, pushing the boundaries of miniature computing.**

The project, known as uMIPS, is a remarkable feat of engineering and a testament to the power of open-source technology. It leverages an 8-bit AVR microcontroller and a MIPS instruction set to create a tiny, but functional, Linux system.

The project’s creator, who goes by the username “skeeto” online, has been refining his design for years, continually pushing the limits of what’s possible on such a small scale. The initial 2012 version was a novelty but suffered from agonizing boot times (over 6 hours) and slow performance.

The current iteration, however, boasts a significantly improved user experience. The computer now boots in under 3 minutes and is fast enough to run a basic Linux environment, allowing users to compile programs, browse the internet, and even run a full GUI.

The tiny computer relies on a complex combination of hardware and software solutions:

* **Microcontroller:** An ATSAMD21 series chip from Atmel (now Microchip) serves as the brain of the system. It features a built-in USB interface and QSPI support for interfacing with external memory.
* **Memory:** The computer uses four Quad SPI (QSPI) PSRAM chips for memory, providing a total of 32 MB of RAM.
* **Storage:** The system utilizes a microSD card for storage, holding the Linux operating system and user files.
* **Communication:** It communicates with the outside world via two virtual serial ports that are accessible through a USB-C connection.

One of the biggest challenges facing the project was the limited resources of the microcontroller. The creator had to overcome limitations in memory, processor speed, and the Atmel chip’s notoriously buggy DMA engine. To address these issues, the project utilizes a variety of optimizations:

* **Instruction Cache:** A 2 KB instruction cache helps improve performance by reducing the need to access external memory.
* **L2 Cache:** A 2 KB L2 cache further accelerates memory access, compensating for the slow QSPI RAM.
* **Software MMU:** Instead of relying on a hardware Memory Management Unit (MMU), the computer utilizes a software-based MMU, where the operating system manually manages the TLB (Translation Lookaside Buffer).
* **Bit-Banging SPI:** To overcome the limitations of the Atmel chip’s SPI units, the creator implemented bit-banging SPI, achieving significantly faster speeds for external memory access.
* **Hypercalls:** The system utilizes hypercalls – a specialized instruction – to communicate with the emulator and manage various functions like memory mapping and SD card access.

Despite these challenges, the uMIPS project stands as a remarkable achievement. It demonstrates the power of ingenuity and open-source development, showcasing the incredible potential for tiny computers to perform complex tasks.

The project’s creator provides detailed instructions, schematics, source code, and even a pre-built image, allowing hobbyists to build their own Linux business card computer. The uMIPS project continues to evolve, with ongoing improvements and potential support for other operating systems like Ultrix and NetBSD.

The uMIPS project stands as a testament to the power of small computers and the creativity of those who push the boundaries of technology. It’s a reminder that even with limited resources, we can achieve incredible feats of engineering.

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