Web service is a common Internet application that enables interactions of machines over a network. As to establish ubiquitous Internet, enabling Web services on embedded systems is certainly among the development trend in near future. This paper presents an implementation of REST style or RESTful Web services on embedded system. The prototype had been implemented using a Xilinx Spartan-3E Starter FPGA board for home device control application on a 100Mbps LAN environment.

The growth of XML usage raises the necessity for embedded XML parser implementation. Embedded systems differed from conventional computing platforms for its limited resources. Among existing XML parsers, SAX and VTD-XML appear to be potential candidates for embedded implementation. The former utilizes minimum resources to perform forward-only XML streaming; while the latter provides random access to XML document at moderate resources. This paper proposes a new idea of Roll-Back Streaming XML (RBStreX) parser for embedded XML parsing. RBStreX is a "pull" type SAX parser that can perform backward referencing through its "roll-back" mechanism. Its resource requirement is only slightly higher than that of SAX and much lower than that of VTD-XML. A simple RBStreX had been designed using VHDL and simulated using Altera Quartus II software.

This Communication reports on FPGA prototyping of an embedded web service that sends XML messages under two different packages, namely Simple Object Access Protocol (SOAP) and Representational State Transfer (REST). The request and response messages are communicated through a 100 Mbps local area network between a Spartan-3E FPGA board and washing machine simulator. The performances of REST-based and SOAP-based web services implemented on reconfigurable hardware are then compared. In general, the former performs better than the latter in terms of FPGA resource utilization (~12% less), message length (~57% shorter), and processing time (~4.5 μs faster). This work confirms the superiority of REST over SOAP for data transmission using reconfigurable computing, which paves the way for adoption of these low-cost systems for web services of consumer electronics such as home appliances.