The Applications group in Figure 3 includes functions such as modem-level DSP, link and network protocols, I/O access, and security services. The applications must use the CF Interfaces and Services and consist of one or more Resources. The resource interface provides a common Applications Programming Interface (API) for the control and configuration of software components.
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The various hardware elements of a SCA-compliant radio are referred to as Devices, and they can include general-purpose processors (GPPs), A/Ds, D/As, digital receivers, upconverters, field-programmable gate arrays (FPGAs), DSPs, and other types of equipment.
From a software point of view, the software proxies that act to interface to the hardware also are referred to as Devices. This may be a little confusing, but in the overall theme it does work since all communications to the underlying hardware must flow through these structures.
Devices are divided into four classes. Simple elements like A/D and D/A converters that require basic control monitoring and data connections are called Devices. More complex elements like GPPs capable of accepting and executing program code are called ExecutableDevices.
An FPGA is capable of performing a signal-processing function, but typically it cannot really execute program code although embedded PowerPC cores in the FPGAs can do some execution. In general, FPGAs first must be configured for a particular task, so they're called LoadableDevices.
The fourth class of a Device is a combination of Devices, so it's termed the AggregateDevice. An example of this class would be a board that contains both A/Ds and FPGAs.
Adapters
Adapters are Resources or Devices used to support non-CORBA-compatible elements in the domain. For that reason, Adapters provide that translation between the non-CORBA-compatible component and the CORBA-compatible resources.
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Since an Adapter implements the CF CORBA interface known to other CORBA-compatible resources, the translation service should be transparent to the CORBA-compatible resources. Some examples of Adapters are modems, security I/O, and host processing elements.
FPGA Technology in Software-Defined Radios
FPGAs are a crucial part of many SDR systems due to the outstanding performance they provide. While dynamic loading and control of FPGAs still are not mature parts of the SCA specification, FPGAs can be preconfigured to extend the hardware performance and functions of a system component outside the SCA specification. Some of their key advantages include the following:
- Replacement for Interfacing and Glue Logic: The FPGA flexible I/O pins can mimic various logic levels to implement a wide range of high-performance interfaces to components, buses, memory devices, and communications ports.
- Control Structures: The FPGA includes specialized hardware structures such as synchronous DRAM controllers for target memories. An advanced dual-clocking, timing, and synchronization system built into the FPGA logic simplifies data acquisition and timestamping and supports multichannel operation.
- Custom Signal Processing: The FPGA also provides custom signal processing afforded by its DSP structures such as block RAM, hardware multipliers, and logic slices. You can add your own IP or install commercial off-the-shelf (COTS) IP for specialized tasks. This often saves months of development time and offloads signal processing chores from other processors in the system. In this role, this newly acquired function of the FPGA often is fixed during deployed operation.
- Reconfigurability: In this role, the FPGA often is reconfigured during system initialization or run time, based on the current needs of the application. Here is where FPGAs will further extend the scope of software-defined radios.
- PowerPC Processors: The on-chip PowerPC processors can be equipped with an OS and programmed to execute C code. Since the processors are surrounded by a wealth of device interfaces, memory, and real-time signal processing hardware, they may not be allocated as freely as a generic processor within a pool of GPPs. However, these immediate resources could be extremely efficient for data flow and real-time processing tasks.
