Section: New Results

Software Radio Programming Model

Software defined radio (SDR) technology has evolved rapidly and is now reaching market maturity. However, no standard has emerged for programming the new type of machine that will manage the access to the radio channel. Mickaël Dardaillon, Kevin Marquet, Tanguy Risset have been working in collaboration with the CEA LETI on compiling waveform for heterogeneous Multi-processor SoCs . This research leaded to a prototype compiler for the Magali MP-SoC developped in Mickael Dardaillon' PhD thesis (passed in November 2014) which was the first attempt to compile the spdf format to a real architecture [18] , [16] , [17] . This study highlighted in particular the fact that spdf was a good computation model for waveform description langage, easier to compile than dynamic dataflow format.

To enable non-trivial computation on very resource-constrained platforms powered by energy harvested from RF communications, an embedded OS has to save and restore program state to and from non-volatile memory. By doing so, the application program does not lose all progress when power is lost, which happens very often in environmentally-powered systems. This can be achieved [13] thanks to an incremental checkpointing scheme which aims at minimizing the amount of data written to non-volatile memory, while keeping the execution overhead as low as possible.

A VHDL implementation of the three available options of the IEEE 802.15.4 physical layer was developed [29] in the context of FIT/CorteXlab. This parametrized design was validated on a Nutaq platform which combines Xilinx Virtex-6 FPGA and tunable Radio420x RF transceiver. This work participates to the building of an open source hardware SDR library similar to GNU radio but targeted to FPGA-based platforms.

A FIR filter is specified by its coefficients (real numbers) and its input and output formats. The implementation of a FIR should be as accurate as its output format allows, but no more. This very simple specification enables the automatic construction of FIR filter implementations that are provably accurate at a minimal hardware cost [19] . The corresponding FIR generator is available in FloPoCo.

The fixed-point Atan2 function is very useful to recover the phase of a complex signal. A careful study of three implementation techniques (including a novel one based on two-variable quadratic approximation) shows that, on current FPGAs, the good old CORDIC technique is more efficient than multiplier-based techniques [46] .