sditch - (micro)SD (sw)itch - microSD card mux control script
This is a script designed to run on a Raspberry Pi to control a microSD card MUX, switching a microSD card between a USB card reader/writer and a single-board computer (SBC such as another Raspberry Pi or similar). This allows the microSD card to be (re)imaged or copied, and the SBC to be booted from that card, without physical access -- good for automated testing (and remote access during a pandemic!)
The actual MUX hardware consists of a pair of sn74sbt3257 chips interfaced to the control computer through GPIO lines. One GPIO controls the !OE (not output enable, i.e., output disable) line and the other controls the S (select) line on the mux chips. The A inputs on the chips are connected to the microSD card socket, and the B1/B2 outputs are connected to two microSD outputs (we used the SparkFun microSD card sniffers to provide the microSD card connectors to plug into the two devices; we may produce a single thin PCB in the future, and will publish the board design if we do so).
The script is also designed to manage a PDU controlling the SBC; it's set for a Raritan PDU at this point but this can be readily adjusted.
These are the commands accepted by the script:
- status - status of the microSD mux
- muxoff - microSD card not connected (mux off)
- pi - microSD card connected to Pi
- reader - microSD card connected to reader
- [re]boot - microSD card connect to Pi, Pi started
- poweron - ...same as boot
- poweroff - shutdown and poweroff the Pi
- shutdown - ...same as poweroff
- read file - microSD card contents placed in file (.gz)
- write file - microSD card written from file (.gz)
- writeon file - ...write followed by poweron
- mount - microSD card partitions mounted under /mnt/sd
- serial - start minicom for serial console monitoring
- video - start a video stream for attached CSI camera (useful for watching a video monitor)