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One truly unique aspect of FPGA-based prototyping for validating SoC design is its ability to work standalone. This is because the FPGAs can be configured, perhaps from a flash EEPROM card or other self-contained medium, without supervision from a host PC. The prototype can therefore run standalone and be used for testing the SoC design in situations quite different to those provided by other modeling techniques, such as emulation, which rely on host intervention.
In extreme cases, the prototype might be taken completely out of the lab and into real-life environments in the field. A good example of this might be the ability to mount the prototype in a moving vehicle and explore the dependency of a design to variations in external noise, motion, antenna field strength and so forth. For example, the authors are aware of mobile phone baseband prototypes which have been placed in vehicles and used to make on-the-move phone calls through a public GSM network.
Chip architects and other product specialists need to interact with early adopter customers and demonstrate key features of their algorithms. FPGA-based prototyping can be a crucial benefit at this very early stage of a project but the approach is slightly different to the mainstream SoC prototyping.
Another very popular use of FPGA-based prototypes out of the lab is for pre- production demonstration of new product capabilities at trade shows. We will explore the specific needs for using a prototype outside of the lab in Chapter 12 but for now let’s consider a use of FPGA-based prototyping by the Research and Development division of The BBC in England (yes, that BBC) which illustrates both out-of-lab usage and use at a trade-show.
The powerful ability of FPGAs to operate standalone is demonstrated by a BBC Research & Development project to launch DVB-T2 in the United Kingdom. DVB-T2 is a new, state-of-the-art open standard, which allows HD television to be broadcast from terrestrial transmitters.
The reason for using FPGA-based prototyping was that, like most international standards, the DVB-T2 technical specification took several years to complete, in fact 30,000 engineer-hours by researchers and technologists from all over the world. Only FPGAs gave the flexibility required in case of changes along the way. The specification was frozen in March 2008 and published three months later as a DVB Blue Book on 26 June 2008.
Because the BBC was using FPGA-based prototyping, in parallel with the specification work, a BBC implementation team, led by Justin Mitchell from BBC Research & Development, was able to develop a hardware-based modulator and demodulator for DVB-T2.
The modulator, shown in Figure 19, is based on a Synopsys HAPS ® -51 card with a Virtex-5 FPGA from Xilinx. The HAPS-51 card was connected to a daughter card that was designed by BBC Research & Development. This daughter card provided an ASI interface to accept the incoming transport stream. The incoming transport stream was then passed to the FPGA for encoding according to the DVB-T2 standard and passed back to the daughter card for direct up-conversion to UHF.
Figure 19: DVB-T2 prototype at BBC Research and Development (Source: BBC)
The modulator was used for the world’s first DVB-T2 transmissions from a live TV transmitter, which were able to start the same day that the specification was published.
The demodulator, also using HAPS as a base for another FPGA-based prototype, completed the working end-to-end chain and this was demonstrated at the IBC exhibition in Amsterdam in September 2008, all within three months of the specification being agreed. This was a remarkable achievement and helped to build confidence that the system was ready to launch in 2009.
BBC Research & Development also contributed to other essential strands of the DVB-T2 project including a very successful "PlugFest" in Turin in March 2009, at which five different modulators and six different demodulators were shown to work together in a variety of modes. The robust and portable construction of the BBC’s prototype made it ideal for this kind of PlugFest event.
Justin explains what FPGA-based prototyping did for them as follows:
“One of the biggest advantages of the FPGA was the ability to track late
changes to the specification in the run up to the transmission launch date. It
was important to be able to make quick changes to the modulator as changes
were made to the specification. It is difficult to think of another technology that
would have enabled such rapid development of the modulator and demodulator
and the portability to allow the modulator and demodulator to be used
standalone in both a live transmitter and at a public exhibition.”
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