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Vulcan µarch
General Info
Arch Type	CPU
Designer	Broadcomm, Cavium
Manufacturer	TSMC
Introduction	2018
Process	16 nm
Core Configs	16, 20, 24, 28, 30, 32
Pipeline
Type	Superscalar, Superpipeline
OoOE	Yes
Speculative	Yes
Reg Renaming	Yes
Stages	13-15
Decode	4-way
Instructions
ISA	ARMv8.1
Extensions	NEON
Cache
L1I Cache	32 KiB/core 8-way set associative
L1D Cache	32 KiB/core 8-way set associative
L2 Cache	256 KiB/core 8-way set associative
L3 Cache	1 MiB/core
Succession
XLP II

Vulcan is a 16 nm high-performance 64-bit ARM microarchitecture designed by Broadcom and later Cavium for the server market.

Introduced in 2018, Vulcan-based microprocessors are branded as part of the ThunderX2 family.

History

Vulcan can trace its roots all the way back to Raza Microelectronics XLR family of MIPS processors from 2006. With the introduction of their XLR family in 2009, Raza (and later NetLogic) moved to a high-performance superscalar design with fine-grained 4-way multithreading support. In 2011, Broadcom acquired NetLogic Microsystems and integrated them Broadcom's Embedded Processor Group.

In 2013, Broadcom announced that they have licensed the ARMv7 and ARMv8 architectures, allowing them to develop their own microarchitectures based on the ISA. Vulcan is the outcome of this effort which involved adopting the ARM ISA instead of MIPS and enhancing the cores in various ways.

In 2017 Cavium acquired Vulcan from broadcom which was introduced later that year. In early 2018, Vulcan-based microprocessor entered general availability under the ThunderX2 brand.

Architecture

Vulcan builds on the prior MIPS-based XLP II microarchitecture. The design has been substantially improved and changed to execute ARM (based on the ARMv8.1 ISA).

Key changes from XLP II

• Converted to ARM ISA (from MIPS)
  • Aarch64, Aarch32
• 16nm FinFET process (from 28 nm planar)
• 40% IPC improvement
• 25% higher clock (2.5 GHz, up from 2 GHz)
• Core
  • Longer pipeline (15 stages, up from 13)
  • Improved branch predictor
  • Double fetch throughput (4, up from 2)
  • New Decoder
    • Decodes ARMv8.1 (Instead of MIPS64 R5)
    • Decodes to micro-ops
      • Roughly 10-20% more µOPs
  • New loop buffer
  • Execution Engine
    • New scheduler
      • Unified schedule (from distributed)
        • 60 entries
    • Large ROB (180 entries, up from 128)
    • Execution Units
      • New FP Unit (2, up from 1)
      • Wider FP Units (128-bit, up from 64-bit)
  • Memory Subsystem
    • Double load bandwidth (128-bit, up from 64-bit)
    • New Store Data Unit
    • Half L2 Cache Size (256 KiB, down form 512 KiB)
• Memory Controller
  • DDR3 → DDR4
  • 4 → 8 channels
  • 1600 MT/s → 2666 MT/s
  • 47.68 GiB/s → 158.9 GiB/s

Block Diagram

Entire Chip

Individual Core

Memory Hierarchy

• Cache
  • L1I Cache
    • 32 KiB, 8-way set associative
  • L1D Cache
    • 32 KiB, 8-way set associative
  • L2 Cache
    • 256 KiB, 8-way set associative
  • L3 Cache
    • 1 MiB/core slice
    • Shared
  • System DRAM
    • 8 Channels
    • DDR4, up to 2666 MT/s
    • 8 B/cycle/channel (@ memory clock)
    • ECC
• TLBs
  • ITLB
    • Dedicated instruction TLB
    • DTLB
      • TLB unit for each LSU
  • STLB
    • 2048-entry
    • 4 KiB - 16 GiB pages

Overview

Scaled up from prior architectures in all vectors (performance, area, and TDP), Vulcan was designed to be a Xeon-class ARM-based server microprocessor. Vulcan features 32 high-performance custom-designed ARM cores fully compliant with ARMv8.1 along with their accompanying 1 MiB of level 3 cache slice (for a total of 32 MiB of shared last level cache). Since each core supports up to four simultaneous threads, the full configuration can support up to 128 threads. Supporting a large number of cores, are eight DDR4 channels capable of data rates of up to 2,666 MT/s, allowing for 170.7 GB/s of aggregated bandwidth.

The processor comes with 14 fully-configurable PCIe Gen3 controllers with 56 available lanes. The chip also has 2 USB 3 and 2 SATA 3 ports.

Vulcan supports up to two-way multiprocessing through their second-generation Cavium Coherent Processor Interconnect (CCPI2) capable of providing 600 Gbps of aggregated bandwidth.

Core

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All Vulcan Chips

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References

• Some information was obtained directly from Broadcom
• Some information was obtained directly from Cavium

See also

• Qualcomm's Falkor
• Intel's Skylake