Field programmable gate arrays with hardwired networks on chip

Abstract

Technology down-scaling and platform-based designs have enforced a number of application and architecture trends for system-on-chip (SOC) designs. A modern SOC is now a multi-functional machine that can execute a large number of complex applications by using tens or even hundreds of intellectual properties (IPs). Meanwhile, due to a number of constraints, e.g., short time to market, fickle market demands, and high non-recurring engineering (NRE) costs to name a few, Field Programmable Gate Arrays (FPGAs) have gained popularity to implement SOC designs. The applications in an SOC can be dynamically started and stopped thus forming multiple use-cases. The applications can also have diverse Quality-of-Service (QoS) constraints ranging from non real-time to soft, firm, and hard real-time constraints. At the same time the IP cores in an SOC are heterogenous in nature and run at diverse clock frequencies. The IPs can be microprocessors, DSP slices, memories, and ALU units, etc. The increasing number and diversity of applications and IPs require a powerful onchip communication architecture for quick integration and appropriate QoS. In contemporary FPGAs the onchip interconnect would be soft, i.e., programmed in the configurable fabric. The above-mentioned application and architecture trends have triggered a series of problems. (1) An increasing number of applications on an FPGA often requires dynamic reconfiguration of an application, which in turn can produce interference with other running applications. (2) The increasing complexity of an application may mean that it can not be mapped entirely on the FPGA, which in turn can encounter loss of state of data during intra-application dynamic partial reconfiguration. (3) The diverse natures of applications make it difficult to fulfill the Quality-of-Service constraints of an application. (4) Similarly, it is hard to achieve (physical) timing closure in an SOC, because of the increasing number and diversity of the IP cores. (5) The technology downscaling leads to FPGA architectures that are more prone to faults, e.g., configuration memories and logic elements in an FPGA can be stuck at a particular value. (6) Because communication architecture and IPs are both mapped as soft IPs in the same logic plane of the FPGA, their placement has many restrictions to allow for dynamic partial reconfiguration. In this thesis, we aim to address the above-mentioned problems by proposing the architecture and design flow of a new FPGA. As the main contribution of the thesis, we propose the FPGA architecture with a hardwired network on chip (HWNoC), and multiple test, configuration, and functional regions (TCFRs). We call it hardwired, because the NoC in an FPGA is built in silicon and not by using the reconfigurable elements. By having a HWNOC we can have a globally asynchronous locally synchronous (GALS) environment, which in turn ensures that data is not lost during inter-IP communication. The HWNOC separates the communication and computation in two disjoint planes, which alleviates restrictions on the placement of IPs. As the second contribution of the thesis, we show how we can use the HWNOC to transport unified test, configuration, and functional data to TCFRs, for testing, faster configuration, and interference-free communication during execution of applications. As the third contribution of the thesis, we demonstrate that how the proposed design flow ensures predictable application behavior by fulfilling the QoS constraints. We also present a 3-tier reconfiguration model that uses the HWNOC, which ensures contention-free communication at architecture level, to overcome the problems of interference and state-loss during inter-application and intra-application reconfiguration respectively. Another contribution of the thesis is that it proposes a non-intrusive test methodology that uses the HWNOC as a test access mechanism to test the presence of faults reliability of FPGA architecture. In other words, the proposed methodology makes sure that applications are always reconfigured and executed on a reliable region of an FPGA, and without effecting the other running applications.