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PULPonFPGA: Lightweight Virtual Memory Support - Software Cache

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Short Description

While high-end heterogeneous systems-on-chip (SoCs) are increasingly supporting heterogeneous uniform memory access (hUMA) as envisioned by the Heterogeneous System Architecture (HSA) foundation, their low-power counterparts targeting the embedded domain still lack basic features like virtual memory support for accelerators. As opposed to simply passing virtual address pointers, explicit data management involving copies is needed to share data between host processor and accelerators which hampers programmability and performance.

At IIS, we use an evaluation platform based on the Xilinx Zynq-7000 SoC [1] with PULPonFPGA [2] implemented in the programmable logic to study the integration of programmable many-core accelerators into embedded heterogeneous SoCs. We have developed a mixed hardware/software solution to enable lightweight virtual memory support for many-core accelerators in heterogeneous embedded SoCs [3,4]. While our current solution allows the programmer to share virtual address pointers between the host processor and the accelerator in a completely transparent manner, it still requires the programmer to manually orchestrate DMA transfers between the accelerator's low latency tightly-coupled data memory (TCDM), an L1 scratchpad memory, and the shared main memory to optimally exploit the system's memory hierarchy and to achieve high performance.

The idea of this project is to enhance our solution with a software cache similar to [5] that uses part of the TCDM to filter the accelerator's accesses to shared data structures living in main memory, and to spare the programmer from manually setting up the DMA transfers, thereby increasing performance and programmability, respectively. To this end, you will need to:

... Study existing software caches such as [5].
... Design and implement your own software cache suitable for the heterogeneous platform at hand.
... Set up operation on the evaluation platform, and characterize the enhanced solution using heterogeneous benchmark applications.

Status: Available

Looking for Interested Master Students
Supervision: Pirmin Vogel, Andrea Marongiu


20% Theory, Algorithms and Simulation
5% VHDL, FPGA Design
60% Accelerator Runtime Development (C)
5% Linux Kernel-Level Driver Development
10% User-space Runtime and Application Development for Host and Accelerator


VHDL/System Verilog, C
Embedded Linux experience
Experience with Linux kernel-level driver development, GCC and GDB is of advantage.


Luca Benini


  1. Xilinx Zynq-7000 All-Programmable SoC link
  2. PULP link
  3. P. Vogel, A. Marongiu, L. Benini, "Lightweight Virtual Memory Support for Many-Core Accelerators in Heterogeneous Embedded SoCs", Proceedings of the 10th International Conference on Hardware/Software Codesign and System Synthesis (CODES+ISSS'15), Amsterdam, The Netherlands, 2015. link
  4. P. Vogel, A. Marongiu, L. Benini, "Lightweight Virtual Memory Support for Zero-Copy Sharing of Pointer-Rich Data Structures in Heterogeneous Embedded SoCs", IEEE Transactions on Parallel and Distributed Systems, vol. PP, no. 99, 2016. link
  5. C. Pinto, L. Benini, "A Highly Efficient, Thread-Safe Software Cache Implementation for Tightly-Coupled Multicore Clusters", Proceedings of the 24th International Conference on Application-Specific Systems, Architectures and Processors (ASAP'13), Washington, DC, USA, 2013. link
  6. D. J. Sorin, M. D. Hill, D. A. Wood, "A Primer on Memory Consistency and Cache Coherence", Morgan & Claypool Publishers, 2011. link

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