System and Circuit Level Power Modeling of Energy-Efficient 3D-Stacked Wide I/O DRAMs Karthik Chandrasekar TU Delft Christian Weis $, Benny Akesson*, Norbert Wehn $ & Kees Goossens # $ * #

Motivation for 3D-stacking of DRAMs Problem Statement - Power Modeling Circuit-level DRAM architecture & power model System-level DRAM power model (DRAMPower) Comparison: Results and Analysis Summary Overview 19-Mar-131Karthik Chandrasekar / TU Delft

[I/O power per bit: 0.7mW in TSV vs 2.3mW in PoP vs 4.6mW in Off-Chip – Samsung] The Performance Vs. Power Factor Motivation: Why 3D-Stacked DRAMs? 19-Mar-13Karthik Chandrasekar / TU Delft2 Images & Data Courtesy: HMC, JEDEC 42.6, FineTech, Nvidia, Samsung  

An accurate 3D-DRAM Power Model to design DRAM-stacked SoCs What’s missing? [Problem Statement] 19-Mar-13Karthik Chandrasekar / TU Delft3

Circuit-level Power Model – Modeling the DRAM architecture at the circuit-level in SPICE – Pros: Accurate and detailed – Cons: Slow, requires circuit-level understanding of DRAM architecture & technology specifications for DRAMs are publicly unavailable System-level Power Model (like Micron’s) – Based on vendor provided datasheet measures and JEDEC specifications – Pros: Fast, easy to integrate & employs simple models for memory operations – Cons: Accuracy is unclear. Not directly applicable for 3D-DRAMs and is not verified against circuit-level models or hardware measurements. Approaches to power modeling 19-Mar-13Karthik Chandrasekar / TU Delft4 Need: Fast, Simple & Accurate Model

Develop A System-Level 3D-DRAM Power Model i.e. as accurate as What’s the solution? 19-Mar-13Karthik Chandrasekar / TU Delft5 A Circuit-Level 3D-DRAM Power Model

19-Mar-13Karthik Chandrasekar / TU Delft6 Circuit-Level DRAM Modeling Baseline DRAM Model (Weis) DATE‘11 and DAC‘13 NGSPICE - PTM/BSIM 1T1C Cell to Banks 2D to 3D (New) Based on DATE ‘11 & JEDEC Wide IO – x512 4 Banks/Channel 4 Channels TSV Routing – Data, Cmd & Addr – Control, Clock & Power No ODT (On Die Termination) – Low Freq. & IO Capacitance No DLL (Delay Locked Loop) TSV model from IMEC/GaTech

System-Level Power Model (DRAMPower) 19-Mar-13Karthik Chandrasekar / TU Delft7 Problem with Micron’s model: Not directly applicable for 3D-DRAMs (Multiple voltage domains and IO) Accuracy is unclear (State transitions not addressed & Approx. workload used) Not verified against circuit-level models or hardware power measurements. Comparison to Micron model Adapting to 3D-DRAMs: Considers multiple voltage domains: (a) Core (b) Derived (Wordline) Includes IO power consumption (Incl. I/O Pads, Buffers, Bumps, Drivers & Pins) RD operation Energy (Generic equation): Modeling for Accuracy: Models memory state transitions – from active to power-down Models self-refresh accurately (functional correctness & timing difference) Most importantly: Is almost as accurate as the circuit-level model

Self-Refresh Operation - Accuracy 19-Mar-13Karthik Chandrasekar / TU Delft8 MicronSREFNOP SREXNOP Timings< SR EF >< XSDLL > Active Current Bckgnd CurrentIDD6 IDD2N ActualSREFNOP SREXNOP Timings< RFC-RP > < R P >< SREF >< X S > Active Current IDD5- IDD3N IDD5- IDD2N Bckgnd CurrentIDD3P0 IDD2P0 IDD6 IDD2N Actual Internal Refresh No DLL We furnish new equations in the system-level power model to address such accuracy issues

Experiment I: – Different Operations – Different Granularity Results: – Less than 2% difference – Adapted Micron SR (200): 72% diff. Experiment II: – H.263 Encoder & EPIC Encoder – JPEG Encoder & MPEG2 Decoder – Different Loads and Power Modes Results: – Less than 2% difference – Adapted Micron: 12% diff. (SR 500MHz) The 2% difference is due to the use of JEDEC-specified averaged IDD currents. Comparison: Results & Analysis 19-Mar-13Karthik Chandrasekar / TU Delft9 Shows the accuracy of the system-level power model

Key Highlights: Presented an accurate datasheet-based system-level power model for Wide I/O 3D-stacked DRAMs. Verified the system-level model for accuracy against as a detailed SPICE-based circuit-level 3D-DRAM architecture and power model. Observed < 2% difference in power and energy estimates for different memory operations and for any variations in memory load. Other Important Contributions: Provided estimates for IDD current measures for different JEDEC 3D-DRAM configurations, in place of the as yet unavailable datasheets (in the paper). The system-level power model (DRAMPower) has been released online as an open-source 3D-DRAM power estimation tool. Download link: Summary 19-Mar-13Karthik Chandrasekar / TU Delft10