Design and Realization of a Prototype Hardware Platform for ...

The MegaWatch Wireless PlatformMaster's Thesis - Emanuel Corthay6 The MegaWatch Hardware Platform DesignRFCustomPeripheralCustomInterfaceHardwareDataProcessingFPGAStandardBusPeripheralsProcessorMemorySoftwareConfigurationFigure 10 General System PrincipleApplicationSoftwareThe FPGA is basically composed of a large number of logical cells that can implementfundamental logic functions like logical gates, flip-flop and so on. Each cell is configured accordingto a static RAM memory that is loaded at startup from a configuration file sent to the chip. Theresult is a flexible hardware logic system with a software component to configure the embeddedlogic. The FPGA also has drawbacks. It is generally more expensive than an ASIC solution forlarge production, consumes more power (the configuration memory essentially) and runs at lowerfrequency than an ASIC version (fixed wired network). But such a system is very powerful to test adesign (prototyping) before mass production, or for custom, low volume solutions. The reason issimple: you can program a complete system in software that you want your hardware FPGA logicgates to do, and if it does not work as expected, you can simply change the code! The advantageof the software approach (its flexibility) and of the hardware approach (its fast speed for dedicatedtasks) is thus united in a single FPGA circuit.For our application, where flexibility is a requirement, an FPGA solution is ideal. The radiosubsystem can be programmed into this FPGA, changed and tested at will. Also, once a goodradio subsystem runs on the FPGA, a real hardware, gate-level circuit design can be createdautomatically from the FPGA configuration software, and integrated later as part of a dedicatedASIC circuit.6.3.2 Design choiceAltera has a chip family called Excalibur with the nice property of having both an FPGA andcomplete ARM9 processor system in a single chip. It also has the appropriate and integrated toolsto easily combine an FPGA and ARM design into a powerful and versatile system.Moreover, a Linux distribution for the ARM processor architecture exists and is being activelydeveloped as a joint and distributed free software effort around the globe. This last argument setthe operating system that will be used to Linux as the application development environment.The selected Altera Excalibur ARM EPXA1F484C3 [15] chip has the following characteristics:• An ARM922T processor running at 133 MHz• A SDRAM SDR and DDR memory controller (512 Mo max)• Internal 32 Ko SRAM memory• Internal 16 Ko double access SRAM memory• External memory interface of maximum 4 times 32 Mo• Interrupt controller, UART and timers• FPGA with 100’000 logical gates running at 24 MHz26 / 83