It's amazing how much functionality you can now squeeze into a small USB stick. Here's what we'll be putting into ours, together with some photographs of our pre-production prototypes.
The USB device shown here is the central component for constructing our IEEE 802.15.4 based wireless networks. The hardware design has been finished for some time and we have been making extensive use of this pre-production build for internal software development.
On the top of the PCB is the radio module which we selected for the initial design. The module is supplied by ST Microelectronics and features their SN260 802.15.4 network coprocessor, which is a rebranded version of the Silicon Labs EM260 device. This configuration will be used for our initial production run of beta testing devices, after which we plan to replace the module with our own fully integrated radio design.
On the reverse side of the PCB is an ARM Cortex M3 microcontroller which runs all the real-time code that is required for managing the wireless network. It also provides support for interfacing to the host system via USB. The microcontroller used here is the ST Microelectronics STM32-F103RE device, which provides adequate flash storage to hold both the executable application code and firmware upgrade images. This will allow us to release firmware upgrades that can easily be installed over the standard USB interface.
We decided to use the eCos real time operating system as the basis for application development on the ARM microcontroller. This is a fully featured open source RTOS which supports a range of popular embedded platforms. As part of porting eCos to our own hardware we made a number of contributions to the publicly available STM32 port, including the USB driver implementation. We are currently using the latest public CVS version of eCos which is available from the eCos project website.
The design shown here will form the basis of a strictly limited release of uncertified development kits for beta test customers. We are aiming to make these kits available to interested developers later in the year, and we will be providing more details once we have finalised our manufacturing arrangements.