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Siracusa: A 16 nm Heterogeneous RISC-V SoC with At-MRAM Neural Engine for Energy-Efficient Extended Reality Computing


Concepts de base
Siracusa is a 16 nm heterogeneous SoC that tightly integrates a RISC-V core cluster with a novel At-MRAM neural engine to enable energy-efficient deep learning inference for extended reality applications.
Résumé

The paper introduces Siracusa, a 16 nm heterogeneous system-on-chip (SoC) designed for extended reality (XR) applications. Siracusa features a cluster of 8 RISC-V cores and a specialized neural network accelerator called N-EUREKA, which is tightly coupled to a 4 MB on-chip MRAM memory for storing neural network weights.

The key highlights of the Siracusa SoC are:

  1. Heterogeneous Architecture: Siracusa combines a RISC-V core cluster for general-purpose computing and signal processing with the N-EUREKA neural network accelerator. The two compute engines share a low-latency 256 KB L1 memory for efficient collaboration.

  2. At-MRAM Integration: N-EUREKA is tightly coupled to a 4 MB on-chip MRAM memory subsystem, enabling high-bandwidth, low-latency access to neural network weights. This "At-MRAM" integration achieves 1.7x higher throughput and 3x better energy efficiency compared to using MRAM as background memory.

  3. Scalable Weight Memory: Siracusa also includes a 4 MB SRAM tile memory that can be used as additional weight storage for larger neural networks, allowing the system to scale to more complex workloads.

  4. Efficient Collaboration: The RISC-V cores and N-EUREKA accelerator efficiently collaborate through the shared L1 memory, with a configurable priority arbiter managing their access to maximize performance and energy efficiency.

The fabricated Siracusa SoC prototype achieves a peak energy efficiency of 8.84 TOp/J for DNN inference, with an area efficiency of 65.2 GOp/s/mm^2. It demonstrates the benefits of tightly integrating non-volatile memory with a specialized neural network accelerator for energy-efficient edge computing in XR applications.

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Stats
The Siracusa SoC achieves a peak operating frequency of 360 MHz in the Cluster domain and 180 MHz in the MRAM domain at 0.8 V. At this voltage, the total power consumption of the Cluster, including the MRAM, is 332 mW. Scaling the Cluster voltage to 0.65 V reduces the power consumption by 2.2x to 151 mW, while the maximum frequency drops to 210 MHz. The octa-core RISC-V Cluster achieves a peak throughput of 120.6 GOp/s at 1.13 TOp/J for 2-bit operands, 57.5 GOp/s at 485 GOp/J for 4-bit operands, and 28.4 GOp/s at 241 GOp/J for 8-bit operands under nominal conditions.
Citations
"Siracusa couples an octa-core cluster of RISC-V digital signal processing cores with a novel tightly-coupled "At-Memory" integration between a state-of-the-art digital neural engine called N-EUREKA and an on-chip NVM based on magnetoresistive memory (MRAM), achieving 1.7× higher throughput and 3× better energy efficiency than XR SoCs using NVM as background memory." "The fabricated SoC prototype achieves an area efficiency of 65.2 GOp/s/mm2 and a peak energy efficiency of 8.84 TOp/J for DNN inference while supporting complex, heterogeneous application workloads, which combine ML with conventional signal processing and control."

Questions plus approfondies

How can the Siracusa SoC be extended to support even larger neural networks that do not fit entirely in the on-chip MRAM and SRAM memories?

To support larger neural networks that exceed the capacity of the on-chip MRAM and SRAM memories, the Siracusa SoC can be extended through several strategies: Off-Chip Memory Expansion: One approach is to incorporate external memory interfaces, such as DDR or HBM, to offload the excess data from the on-chip memories. This allows for seamless integration of larger neural networks without compromising performance. Hybrid Memory Systems: Implementing a hybrid memory system that combines on-chip MRAM and SRAM with off-chip DRAM can provide a scalable solution for accommodating larger neural networks. This approach leverages the speed of on-chip memories and the capacity of off-chip DRAM. Memory Compression Techniques: Utilizing memory compression algorithms can help reduce the memory footprint of neural networks, allowing them to fit within the constraints of the on-chip memories. Techniques like weight pruning, quantization, and sparsity can be employed to optimize memory usage. Dynamic Memory Management: Implementing dynamic memory management techniques that prioritize data movement based on the current processing requirements can help efficiently utilize the available on-chip and off-chip memory resources. By implementing these strategies, the Siracusa SoC can effectively support larger neural networks that exceed the capacity of the on-chip MRAM and SRAM memories while maintaining high performance and efficiency.

What are the potential drawbacks or limitations of the At-MRAM integration approach compared to alternative non-volatile memory integration schemes, such as in-memory computing?

While the At-MRAM integration approach offers several advantages, such as high density, non-volatility, and efficient data access, there are potential drawbacks and limitations compared to alternative non-volatile memory integration schemes like in-memory computing: Limited Write Endurance: MRAM technology has limited write endurance compared to SRAM, which can impact the longevity and reliability of the memory subsystem. Frequent write operations may degrade the MRAM cells over time, leading to potential reliability issues. Slower Write Speeds: MRAM typically has slower write speeds compared to SRAM, which can introduce latency in write-intensive applications. This can affect the overall performance of the system, especially in scenarios where rapid data updates are required. Higher Power Consumption: MRAM may consume more power during write operations compared to SRAM, leading to increased energy consumption. This can impact the overall energy efficiency of the system, especially in applications with frequent write activities. Complex Integration: Integrating MRAM into the system architecture requires specialized design considerations and may introduce complexity in the overall system design. Ensuring seamless communication and data transfer between MRAM and processing units can be challenging. Cost Considerations: MRAM technology may be more expensive than alternative memory technologies, which can impact the overall cost of the system. Cost considerations need to be taken into account when opting for an At-MRAM integration approach.

How could the Siracusa architecture be adapted to support emerging AI workloads beyond computer vision, such as natural language processing or speech recognition, while maintaining its energy efficiency and performance advantages?

To adapt the Siracusa architecture to support emerging AI workloads beyond computer vision, such as natural language processing (NLP) or speech recognition, while maintaining energy efficiency and performance advantages, the following strategies can be implemented: Specialized Accelerators: Integrate specialized accelerators tailored for NLP tasks, such as recurrent neural networks (RNNs) or transformers, to efficiently process sequential data. These accelerators can be optimized for specific NLP operations like attention mechanisms or language modeling. Flexible Memory Hierarchy: Enhance the memory hierarchy to support the unique data access patterns of NLP workloads. Implement memory structures optimized for sequential data processing and large-scale language models to minimize data movement and maximize efficiency. Dynamic Power Management: Implement dynamic power management techniques to adapt the power consumption based on the workload requirements. By intelligently scaling the power of different components based on the workload, energy efficiency can be optimized without compromising performance. Heterogeneous Computing: Utilize a heterogeneous computing approach by integrating different types of processing units, such as CPUs, GPUs, and accelerators, to handle diverse AI workloads effectively. This allows for workload-specific optimization and efficient resource utilization. Software Optimization: Collaborate with software developers to optimize algorithms and models for the Siracusa architecture. Implement efficient software frameworks and libraries that leverage the hardware capabilities of the SoC for NLP and speech recognition tasks. By incorporating these strategies, the Siracusa architecture can be adapted to efficiently support a wide range of emerging AI workloads beyond computer vision, ensuring high performance, energy efficiency, and scalability for NLP and speech recognition applications.
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