Platforms are particular physical FPGA systems. The set of local devices offered varies from platform to platform. Some offer local DDR memory and some offer high-speed serial connections. The actual wired platform interface to a given class of devices may also vary from platform to platform. For example, the wired interface to local memory may change from Avalon to AXI.
AFUs must attach to platform interfaces through an AFU top-level interface. The code in the platforms tree bridges the gap between platform offerings and AFU requirements. AFUs declare their top-level interface class, platforms declare the set of interfaces they offer, and the afu_platform_config script attempts to bridge the gap by defining a shim between the platform's interface and the AFU's expectations. Often this is merely a matching of wires, perhaps transforming wire names or repackaging them in SystemVerilog interfaces.
AFU requirements are defined in afu_top_ifc_db. The schema is defined in the README file. AFU writers may also write their own JSON classes. AFUs declare their interface requirements in the AFU's packager JSON file, using syntax described in README_AFU. Users may add directories containing their own top-level interface specifications to afu_platform_config's search path. Execute afu_platform_config --help for details.
The platform_db directory holds descriptions of interfaces offered by specific platforms. This includes the set of available local devices, the width and number of banks of local memory, etc. Like AFU requirements, the set of directories searched for platform databases may be extended using an environment variable. See afu_platform_config --help. The platform database also holds tuning parameters, such as optimal buffer depths for CCI-P read and write requests. Tuning parameters are exposed in SystemVerilog packages in platform_if/rtl/device_cfg.
The platform_if tree holds SystemVerilog files with standard device interfaces and configuration files for loading the RTL into both Quartus and simulators. Most RTL will:
`include "platform_if.vh"Scripts generated by afu_platform_config will automatically add the directory holding platform_if.vh to the search path.