Bitstream Database-Driven FPGA Programming Flow Based on Standard OpenCL

Abstract

Field-programmable gate array (FPGA) vendors provide high-level synthesis (HLS) compilers with accompanying OpenCL runtimes to enable easier use of their devices by non-hardware experts. However, the current runtimes provided by the vendors are not OpenCL-compliant, limiting the application portability and making it difficult to integrate FPGA devices in heterogeneous computing platforms. We propose an automated FPGA management tool AFOCL, with a guiding principle that the software programmer should only need to use the standard OpenCL API to manage FPGA acceleration tasks. This improves portability since the same OpenCL program will work on any OpenCL-compliant computation device able to execute the same kernels, including CPUs, GPUs, and FPGAs. The proposed approach is based on pre-optimized FPGA bitstreams implementing well-defined OpenCL built-in kernels. This enables a clean separation of responsibilities between a hardware developer preparing the FPGA bitstreams containing the kernel implementations, a software developer launching computation tasks as OpenCL built-in kernels, and a bitstream distributor providing preoptimized FPGA IPs to end-users. The automated FPGA programming tool fetches bitstream files as needed from the distributor, reconfigures the FPGA, and manages the communication with the accelerator. We demonstrate that it is possible to achieve similar performance as the current FPGA vendor OpenCL implementations, while abstracting all FPGA-specific details from the software programmer. The cross-vendor potential of AFOCL is shown by porting the implementation to FPGAs from two different vendors (AMD and Altera), and to two different FPGA types PCIe and system-on-chip (SoC), and controlling all these systems with the same OpenCL host program.