NetSD: Remote Access to Integrated SD Cards of Embedded Devices

Digitalization continuously pervades all areas and the Internet of Things (IoT) is still on the rise. This leads to an increased need for efficiency in the development of embedded devices and systems composed thereof. Hybrid testbeds are common environments to representatively assess, e.g., hardware-software interaction, interoperability, and scalability. Although automation is inevitable to achieve efficiency, not all devices offer interfaces to be fully software-controlled. Most notably, block devices tend to be inaccessible for software outside a Device under Test (DuT), especially when the latter is in a dysfunctional state. This paper introduces the Networked SD card (NetSD) which enables remote access to removable block devices. The proposed system consists of a hardware part, which enables multiplexed access to a block device (e.g., an SD card) and a software part which enables remote access to the block device (e.g., via HTTP or network block device). NetSD thus adds testing and automation possibilities to DuTs without the need to modify their hard- or software. During the hardware design, we fund that different SD transfer modes and access profiles (read or write focus) benefit from different pull-up resistor configurations for the data lines.