Hardware Specific Configurations

Sometimes specialized devices are used to control and manage hardware components. This pages discusses how such devices should be setup and controlled.

USB-SD-Mux from Linux Automation

The USB-SD-Mux is an awesome tool that can mux SD cards into development boards. The main doc for the device is located at linux-automation.com.

Preparing host system

It is recommended to first install the udev rules for the mux, which will make referencing the mux easier. To do this, run the following commands:

git clone https://github.com/pengutronix/usbsdmux.git
cd usbsdmux
sudo cp contrib/udev/99-usbsdmux.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules

When you connect the mux it will be accessible now through sysfs under /dev/usb-sd-mux

$ ls /dev/usb-sd-mux/
id-000000001143

If you want to manually control the mux follow the documentation here.

Special DUT Specific Settings

Since the SD card will be used through a mux at the DUT, it is necessary in some cases to adjust the devicetree. Otherwise the SD card will not be recognized.

Xilinx Carriers

To correctly mount the rootfs the following must be added to the mmc@ff160000 and mmc@ff170000 node in the devicetree:

This is handled automatically by nebula from the CLI or the update_devicetree_for_mux method in the usbmux class.