At Hannover Fair 2007, SERCOS International announced its support for a soft master implementation for SERCOS III. This will make SERCOS III the only bus on the market that offers both hardware and software based master implementations. This would allow SERCOS III users to choose between a software-based interface using off-the-shelf hardware, such as a PC; or current SERCOS III FPGA hardware, which requires minimal development effort and has minimum burden on the CPU. Via such a soft master, control systems and other automation devices that act as master within a SERCOS III network will be able to exchange real-time data with any SERCOS III slave device using a standard Ethernet Controller. SERCOS International announced its willingness to work with any company that is interested in developing such a soft master concept.
In today's SERCOS III, any device with a standard Ethernet interface (e.g., a notebook computer) can be connected directly (without any additional hardware or software) to any unused SERCOS III port without influencing the real-time behaviour or the performance of the SERCOS III real-time network. However, such devices cannot take part in the real-time data exchange. Instead they communicate with the SERCOS III network nodes exclusively using the NRT channel (Non-Real-Time channel). A soft master will allow standard Ethernet devices to exchange both real-time and non-real-time data.
Today's SERCOS III products use a specific SERCOS III hardware for master and slave products. This hardware executes important functions to process the real-time data as fast as possible, as well as to realize the hardware-based synchronization. This approach is also advantageous because the host CPU is not loaded with communication tasks, so that very robust and easily testable designs can be realized.
However, a soft master will make it possible to implement the SERCOS III Master completely in software, replacing SERCOS III hardware by a standard Ethernet controller. SERCOS-specific hardware functions are then moved to the hardware-related and real-time capable portion of a master driver. Such a concept is interesting for PC-based control platforms that already have an Ethernet interface onboard because additional hardware is not required in order to support SERCOS III.
The achievable synchronization accuracy of a SERCOS III real-time network using a soft master is dependant on the performance of the PC hardware and the characteristics of the operating system used. Measurements with off-the-shelf PC hardware in combination with typical real-time operating systems have shown that synchronization accuracy well below 1 µs can be achieved. Thus, even challenging motion applications can be realized.
"The trend to multi-core processor architectures will facilitate the acceptance of soft master solutions in the future, as communication and application tasks can be clearly separated", says Peter Lutz, Managing Director of SERCOS International. "For this reason we regard soft master as a meaningful addition to the existing SERCOS III master hardware designs."