Many modern FPGA-based soft-processor designs must include dedicated hardware modules to satisfy the requirements of a wide range of applications. Not seldom they all do not fit in the FPGA target, so their functionalities must be mapped into the much slower software domain. However, many complex soft-core processors usually underuse the available Block RAMs (BRAMs) when comparing to LUTs and registers. By taking advantage of this fact, we propose a generic low-cost BRAM-based function reuse mechanism (the BRAM-FR) that can be easily configured for precise or approximate modes to accelerate execution. The BRAM-FR was implemented in HDL and coupled to a configurable 4-issue VLIW processor. It was used to optimize different applications that use a soft-float library to emulate a Floating-Point Unit (FPU), and an image processing filter that tolerates a certain level of error. We show that our technique can accelerate the former by 1.23x and the latter by 1.52x, with a Reuse Table that fits in the BRAMs (that would otherwise be idle) of five tested FPGA targets with a marginal increase in the number of slice registers and LUTs.

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Embedded processors must efficiently deliver performance at low energy consumption. Both configurable and reconfigurable techniques can be used to fulfill such constraints, although applied in different situations. In this work, we propose DIM-VEX, a configurable processor coupled with a reconfigurable fabric, which can leverage both design time configurability and runtime reconfigurability. We show that, on average, such system can improve performance by up to 1.41X and reduce energy by up to 60% when compared to a configurable processor at the cost of additional area.

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The well-known Triple Modular Redundancy (TMR), when applied to processors to mitigate the occurrence of faults, implies that all applications have the same level of criticality (since they are all equally protected) and are executed in a homogeneous environment, which naturally would waste precious resources in terms of area and energy. However, many current systems are composed of heterogeneous cores that implement the same ISA (e.g., ARM’s big.LITTLE or DynamIQ), executing some applications that may be more critical than others and that would require different levels of protection. With that in mind, we propose ISA-DTMR, a non-intrusive approach that, taking advantage of heterogeneous systems, can protect applications at different levels in a totally transparent fashion. By using heterogeneous multicore configurations composed of configurable processors that implement the same Instruction Set Architecture (ISA), we will show that it is possible to adapt the level of protection for each application according to its reliability requirements. When compared to homogeneous processors, ISA-DTMR reduces area by up to 54.9%, and energy consumption by 30.35%, with negligible overhead on performance, for a configuration that balances performance and energy consumption. ISA-DTMR is able to provide the same level of protection for critical applications and even improve the reliability for non-critical applications.

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Because of technology scaling, the soft error rate has been increasing in digital circuits, which affects system reliability. Therefore, modern processors, including VLIW architectures, must have means to mitigate such effects to guarantee reliable computing. In this scenario, our work proposes three low overhead fault tolerance approaches based on instruction duplication with zero latency detection, which uses a rollback mechanism to correct soft errors in the pipelanes of a configurable VLIW processor. The first uses idle issue slots within a period of time to execute extra instructions considering distinct application phases. The second works at a finer grain, adaptively exploiting idle functional units at run-time. However, some applications present high instruction-level parallelism (ILP), so the ability to provide fault tolerance is reduced: less functional units will be idle, decreasing the number of potential duplicated instructions. The third approach attacks this issue by dynamically reducing ILP according to a configurable threshold, increasing fault tolerance at the cost of performance. While the first two approaches achieve significant fault coverage with minimal area and power overhead for applications with low ILP, the latter improves fault tolerance with low performance degradation. All approaches are evaluated considering area, performance, power dissipation, and error coverage.@en

It is well-known that different applications exhibit varying amounts of ILP. Execution of these applications on the same fixed-width VLIW processor will result (1) in wasted energy due to underutilized resources if the issue-width of the processor is larger than the inherent ILP; or alternatively, (2) in lower performance if the issue-width is smaller than the inherent ILP. Moreover, even within a single application distinct phases can be observed with varying ILP and therefore changing resource requirements.With this in mind, we designed the ρ-VEX processor, which is a VLIW processor that can change its issuewidth
at run-time. In this paper, we propose a novel scheme to dynamically (i.e., at run-time) optimize the resource utilization by predicting and matching the number of active data-paths for each application phase. The purpose is to achieve low energy consumption for applications with low ILP, and high performance for applications with high ILP, on a single VLIW processor design. We prototyped the ρ-VEX processor on an FPGA and obtained the dynamic traces of applications running on top of a Linux port. Our results show that it is possible in some cases to achieve the performance of an 8-issue core with 10% lower energy consumption, while in others we achieve the energy consumption
of a 2-issue core with close to 20% lower execution time.@en