This PCB Business Card Runs Linux on an Arm Cortex-M0 While Emulating a DECstation
Connects via USB-C without a discrete connector.
PCB business cards are popular among software and hardware enthusiast. Sometimes they are just artwork. Other times they contain a USB-enabled microcontroller that shows up as a keyboard or mass storage device. However, Dmitry Grinberg is a software engineer who took his business card in another direction. LinuxCard emulates a DECStation and runs Linux on an Arm Cortex-M0 core!
LinuxCard measures approximately 50 by 90 millimeters. There are a couple of chips, including the Microchip ATSAMD21E MCU, 3.3 volt linear regulator, and four QSPI RAMs. One side of the board has a Micro SD card socket, and the other features a USB-C connector.
This board is unique in several ways — the first is that the USB-C connector is an edge style. To mate with a cable, the PCB is 0.8 millimeters thick.
The other unique capability of LinuxCard is in its name. The card runs Linux on the ATSAMD21. This chip has a Cortex-M0 core. However, it is not known as a target for Linux Kernels.
Grinberg wrote software that emulates the minimum hardware necessary for a MIPS-based DECstation. And fortunately, this computer has an existing Linux kernel available! The CPU, FPU, MMU, disk drive, and serial controller are all emulated on the SAMD21! Cleverly, the emulation uses several USB CDC/virtual serial ports to connect between the emulated DEC and the modern PC.
One benefit of emulating an older processor technology and targeting a small microcontroller is that all the code for the "computer" to boot fits on a 128 megabyte SD card! Fortunately, Grinberg has an incredibly detailed blog post on emulation details for those interested in the software side of this project.
If you would like a LinuxCard, you need to build one yourself. Fortunately, the gerbers and schematic from the bottom of this post are all you need. (Make sure you download the disk images from the separate link!). Grinberg says that a batch of these may be sold in the future from this Tindie Store.