An interactive Linux computer made from three 8-pin chips
Summary
Dmitry Grinberg builds a hand-solderable computer from three eight-pin chips that runs Debian interactively. The computer consists of a microcontroller, PSRAM and a USB-serial chip. Debian boots with eight megabytes of RAM in about one minute.
Ideas
- A microcontroller emulates the MIPS CPU expected by Linux.
- SPI PSRAM provides eight megabytes of RAM.
- Shared pins connect RAM and SD card through carefully chosen protocol states.
- A custom boot loader updates the firmware from a FAT partition.
- Extreme restrictions make every hardware and software abstraction visible.
Insights
- Artificial limits encourage solutions that standard designs would never require.
- A computer is defined by its capabilities, not by the number of parts or its speed.
- Knowledge of protocols can partly make up for missing pins through time multiplexing.
Facts
- vi, make, objdump and gcc run on the emulated MIPS platform.
Recommendations
- Build with a conservative clock first and check each bus individually.
- Read the schematic, flashing instructions and pin-sharing logic in full before soldering.
References
Links to the original source and the Web Archive open in a new tab.