ARM Powered Rack Mount USB Test Equipment


This is a device which [Limpkin] has been developing at his day job. It’s a high-speed testing interface for use with Physics experiments. We find it interesting because it uses an ARM microcontroller to implement CDC and MSD over USB.

The design is in two parts to make it work in a rack-mount situation. That big white connector allows cards to be swapped out. You can see the board on the right has a USB-A connector. When plugged in this enumerates as a control device (CDC) and a mass storage device (MSD) using fat32 as a file system.

The platform is being developed with open hardware and open source software in mind. If you’re working on a project that uses either of these USB functionalities this makes a swell reference. The ARM Cortex-M3 chip that he’s using is an AT91SAM3U but it should not be too hard to port the code for other similarly-capable ARM processors.

8 thoughts on “ARM Powered Rack Mount USB Test Equipment

    1. From reading the linked article (and looking at the PCB picture up there), I’d guess that the USB mass-storage and control functions aren’t the only work this processor is going to be called upon to perform. From the linked page: “This development platform is primarily aimed at facilitating the realization of high speed (several GHz) functions that quantum physicist need for their experiments, as well as providing data collection capabilities.” I expect the 8 bit Atmega is less capable in the several-GHZ operations regime than the ARM is.

    2. Considering this is a “high speed testing interface”, it almost certainly requires the high speed USB (480Mbit/sec) this 32-bit MCU provides. That alone is reason enough to use it.

      Any 8-bit MCU with USB at best supports 12MBit/sec, 40x slower. But the real speed will be much slower still, limited by the 8-bit MCU; which even if it spends 100% of its time transferring data to USB, can’t keep the pipeline full. You can’t even send real-time 44Khz 16-bit stereo with such a pitiful MCU.

    1. MSC and CDC are both classes defined by the USB-IF. Lay people do indeed call them mass storage devices, but the correct abbreviation is MSC. Don’t believe me…search the spec for MSD and MSC. Also of note, CDC is communications device class…not control.

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