Develop Seamless Interconnection Among Multiple General-Purpose Boards

The control thread instructs the DAC what voltage to output, and it then retrieves the actual voltage value from the ADC in the MCU (Code List 3). Note how the channel to the MCU is used identically to the channel that goes to the DAC, which is simply another thread on the XCore.

Data throughput from this software implementation of the link was low— around 10 kbits/s. Such a software link is ideal for low-data-rate applications, such as the example given. The capability also wasn’t included in the MCU, which would otherwise enable the use of multiple channel ends. Thus, more than one simultaneous connection is disallowed. This could be added easily, though. On larger MCUs, the XMOS system switch’s routing capabilities could be added to the firmware, allowing multiple XMOS Links on one device.

For some applications, an MCU isn’t the right choice. Source is available for XMOS Links in an FPGA at www.xlinkers.org/projects/xlink_fpga.

CONCLUSION
An XMOS Link provides a versatile solution for inter-chip communications and can be readily implemented on a standard microcontroller. Its transition-based nature and credit scheme allows for the possibility of a low-speed link in software. However, the link scales well to very high data rates with minimal overhead. Crucially, inter-chip connections located at the application level are simple, and large complex systems are able to be created without difficulty.

All of the project source code can be found on the Internet at www.xlinkers.org/node/306.