Bufferless software-defined network-on-chip (NoC) is a promising alternative to conventional dynamic routing as it offers predictable data movement with real-time guarantees. Existing time-division multiplexing (TDM)-based mechanisms for predictability assume the worst-case communication pattern (e.g., all-to-all) and compute a fixed schedule wherein the cores can only communicate during the allocated time slots. These approaches lead to low application throughput as they cannot adapt to application characteristics. In this article, we present an application specific, non-TDM-based communication scheduling mechanism for bufferless software-defined NoCs. We choose the synchronous dataflow (SDF) model of computation to represent the input streaming applications. We propose ASCENT, a novel offline approach that takes the SDF-specified streaming application and the NoC architecture as input, exploits the task interactions and the timing information in the SDF, and generates the task-to-core mapping and communication schedule that is represented compactly in hardware. ASCENT achieves$5.8\times $better performance on average than existing TDM-based NoCs and manages to achieve the performance of an ideal dynamically routed NoC, yet ensuring predictability.

The advent of 5G networks motivates the need for high-performance, low-power, time-predictable hardware that can handle the aggressive real-time latency and throughput requirements of baseband processing. With newer generations like 5G, programmable hardware that can adapt readily to network specification updates becomes a critical requirement. We introduce a software-defined array-based many-core architecture, called SPECTRUM, that couples lightweight predictable hardware components with a compiler flow that orchestrates the on-chip hardware resources. This design, by construction, provides timing guarantees with a programmable architecture. Our architecture and compiler flow are designed to support basestation baseband processing computation represented using deterministic Synchronous Data Flow (SDF) model of computation. SDF is commonly used to represent signal processing applications and fits well with real-time systems requirements. We demonstrate substantial power savings with SPECTRUM compared to existing DSPs while meeting the performance requirements.

Wireless communication standards such as Long-term Evolution (LTE) are rapidly changing to support the high data-rate of wireless devices. The physical layer baseband processing has strict real-time deadlines, especially in the next-generation applications enabled by the 5G standard. Existing basestation transceivers utilize customized DSP cores or fixed-function hardware accelerators for physical layer baseband processing. However, these approaches incur significant non-recurring engineering costs and are inflexible to newer standards or updates. Software-programmable processors offer more adaptability. However, it is challenging to sustain guaranteed worst-case latency and throughput at reasonably low-power on shared-memory many-core architectures featuring inherently unpredictable design choices, such as caches and Network-on-chip (NoC). We propose SPECTRUM , a predictable, software-defined many-core architecture that exploits the massive parallelism of the LTE/5G baseband processing workload. The focus is on designing scalable lightweight hardware that can be programmed and defined by sophisticated software mechanisms. SPECTRUM employs hundreds of lightweight in-order cores augmented with custom instructions that provide predictable timing, a purely software-scheduled NoC that orchestrates the communication to avoid any contention, and per-core software-controlled scratchpad memory with deterministic access latency. Compared to many-core architecture like Skylake-SP (average power 215 W) that drops 14% packets at high-traffic load, 256-core SPECTRUM by definition has zero packet drop rate at significantly lower average power of 24 W. SPECTRUM consumes 2.11× lower power than C66x DSP cores+accelerator platform in baseband processing. We also enable SPECTRUM to handle dynamic workloads with multiple service categories present in 5G mobile network (Enhanced Mobile Broadband (eMBB), Ultra-reliable and Low-latency Communications (URLLC), and Massive Machine Type Communications (mMTC)), using a run-time scheduling and mapping algorithm. Experimental evaluations show that our algorithm performs task/NoC mapping at run-time on fewer cores compared to the static mapping (that reserves cores exclusively for each service category) while still meeting the differentiated latency and reliability requirements.

Wireless communication standards such as Long Term Evolution (LTE) are rapidly changing to support the high data rate of wireless devices. The physical layer baseband processing has strict real-time deadlines, especially in the next-generation applications enabled by the 5G standard. Existing base station transceivers utilize customized Digital Signal Processing (DSP) cores or fixed-function hardware accelerators for physical layer baseband processing. However, these approaches incur significant non-recurring engineering costs and are inflexible to newer standards or updates. Software programmable processors offer more adaptability. However, it is challenging to sustain guaranteed worst-case latency and throughput at reasonably low-power on shared-memory many-core architectures featuring inherently unpredictable design choices, such as caches and network-on chip. We propose SPECTRUM, a predictable software defined many-core architecture that exploits the massive parallelism of the LTE baseband processing. The focus is on designing a scalable lightweight hardware that can be programmed and defined by sophisticated software mechanisms. SPECTRUM employs hundreds of lightweight in-order cores augmented with custom instructions that provide predictable timing, a purely software-scheduled on-chip network that orchestrates the communication to avoid any contention and per-core software controlled scratchpad memory with deterministic access latency. Compared to a many-core architecture like Skylake-SP (average power 215W) that drops 14% packets at high traffic load, 256-core SPECTRUM by definition has zero packet drop rate at significantly lower average power of 24W. SPECTRUM consumes 2.11x lower power than C66x DSP cores+accelerator platform in baseband processing. SPECTRUM is also well-positioned to support future 5G workloads.

Coarse-Grained Reconfigurable Arrays (CGRAs) provide high performance, energy-efficient execution of the innermost loops of an application. Most real-world applications, however, comprise of deeply-nested loops with complex and often irregular control flow structures that cannot be mapped to CGRAs by existing compilers. This leads to excessive data transfer costs as the execution continuously alternates between the outer loop-nests on the host processor and the innermost loop on the CGRA accelerator. Moreover, ultra-low power CGRAs can only include limited on-chip memory to cache the configuration bitstreams and need frequent swapping of configurations in the presence of multiple innermost loops. We introduce DNestMap, a partitioning and mapping tool for CGRAs, that can judiciously extract the most beneficial code segments of multiple deeply-nested loops and effectively cache them together statically in the configuration memory through spatio-temporal partitioning. DNestMap achieves 1.58X performance improvement compared to dynamic caching of configuration contexts of the innermost loops in the CGRAs with limited on-chip memory.

Application requirements, such as real-time response, are pushing wearable devices to leverage more powerful processors inside the SoC (system on chip). However, existing wearable devices are not well suited for such challenging applications due to poor performance, and the conventional powerful many-core architectures are not appropriate either due to the stringent power budget in this domain. We propose LOCUS—a low-power, customizable, many-core processor for next-generation wearable devices. LOCUS combines customizable processor cores with a customizable network on a message-passing architecture to deliver very competitive performance/watt—an average 3.1× compared to quad-core ARM processors used in state-of-the-art wearable devices. A combination of full system simulation with representative applications from the wearable domain and RTL synthesis of the architecture show that 16-core LOCUS achieves an average 1.52× performance/watt improvement over a conventional 16-core shared memory many-core architecture. A dynamic power management mechanism is proposed to further decrease the power consumption in both computation and communication, which improves the performance/watt of LOCUS by 1.17×.

CGRAs are promising as accelerators due to their improved energy-efficiency compared to FPGAs. Existing CGRAs support reconfigurability for operations, but not communications because of the static neighbor-to-neighbor interconnect, leading to both performance loss and increased complexity of the compiler. In this paper, we introduce HyCUBE, a novel CGRA architecture with a reconfigurable interconnect providing single-cycle communications between distant FUs, resulting in a new formulation of the application mapping problem that leads to the design of an efficient compiler. HyCUBE achieves 1.5X and 3X better performance-per-watt compared to a CGRA with standard NoC and a CGRA with neighbor-to-neighbor connectivity, respectively.

The requirements' demands of applications, such as real-time response, are pushing the wearable devices to leverage more power-efficient processors inside the SoC (System-on-chip). However, existing wearable devices are not well suited for such challenging applications due to poor performance, while the conventional powerful many-core architectures are not appropriate either due to the stringent power budget in this domain. We propose LOCUS - a low-power, customizable, many-core processor for next-generation wearable devices. LOCUS combines customizable processor cores with a customizable network on a message-passing architecture to deliver very competitive performance/watt - an average 3.1x compared to quad-core ARM processors used in the state-of-the-art wearable devices. A combination of full-system simulation with representative applications from wearable domain and RTL synthesis of the architecture show that 16-core LOCUS achieves an average 1.52x performance/watt improvement over a conventional 16-core shared-memory many-core architecture.