Revision as of 10:31, 2 February 2018

Mongoose 1 (M1) is an ARM microarchitecture designed by Samsung for their consumer electronics. This was Samsung's first in-house developed high-performance low-power ARM microarchitecture.

History

The Mongoose 1 (M1) microarchitecture was Samsung's first in-house design which was done entirely from scratch. A design team was assembled and in roughly 3 years, they've gone from requirements to tape-out. The design was done at Samsung's Austin R&D Center (SARC) which was founded in 2010 for the sole purpose of developing high-performance, low-power, complex CPU and System IPs. A large portion of the design team consists of many ex-AMD Austin engineers as well as ex-IBMers.

Process Technology

M1 was fabricated on Samsung's 14 nm process.

Architecture

The M1 is Samsung's first in-house design from scratch.

• ARM v8.0
  • AARch64 (A64)
  • AARch32 (A32)
    • Thumb support
• 2.6 GHz clock frequency
  • 2.3 GHz for multi-core workloads
• Sub 3-watt/core
• 14 nm process (FinFET)
• Core
  • Advanced branch predictor
  • 4-way instruction decode
    • Most instructions map to a single µOP, with a few exceptions
  • 4-way µOP dispatch and retire
  • Out-of-order execution
    • Out-of-order load and stores
  • Multistride/multistream prefetcher
  • Low-latency and low-power caches

Block Diagram

Core Cluster Overview

Individual Core

Memory Hierarchy

• Cache
  • L1I Cache
    • 64 KiB, 4-way set associative
      • 128 B line size
      • per core
    • Parity-protected
  • L1D Cache
    • 32 KiB, 8-way set associative
      • 64 B line size
      • per core
    • 4 cycles for fastest load-to-use
    • 16 B/cycle load bandwidth
    • 16 B/cycle store bandwidth
  • L2 Cache
    • 2 MiB, 16-way set associative
      • 4x banks (512 KiB each)
    • Inclusive of L1
    • 22 cycles latency
    • 16 B/cycle/CPU bandwidth

Mongoose 1 TLB consists of dedicated L1 TLB for instruction cache (ITLB) and another one for data cache (DTLB). Additionally there is a unified L2 TLB (STLB).

• TLBs
  • ITLB
    • 256-entry
  • DTLB
    • 32-entry
  • STLB
    • 1,024-entry
    • Per core

• BPU
  • 4K-entry main BTB
  • 64-entry µBTB
  • 64-entry return stack

Overview

Mongoose 1 was an entirely brand new architecture from the ground up that implemented the ARMv8 ISA. The architecture supports both AArch64 and AArch32 including Thumb modes. The architecture is a quad-core design which was intended to be paired with another low-power ARM IP core.

Core

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Pipeline

Front-end

Fetch & pre-decoding

With the help of the branch predictor, the instructions should already be found in the level 1 instruction cache. The L1I cache is 64 KiB, 4-way set associative and has its own iTLB consisting of 256 entries. Up to 24 bytes are read from it each cycle into the instruction queue which allows them to hide very short branch bubbles. The instruction queue is a slightly more complex component than a simple buffer. The byte stream gets split up into the ARM instructions its made off, including dealing with the various mis-aligned ARM instructions such as in the case of thumb mode.

Decoding

From the instruction queue the instructions are sent to decode. Decode is a 4-way decoder which can handle both the ARM AArch64 and AArch32 instructions. Up to four µOPs are decoded and sent to the re-order buffer.

Micro-Sequencer

For some complex ARM instructions such as the ARMv7 load-store multiples instructions which result in multiple µOPs being emitted, M1 has a side micro-sequencer that will get invoked and emit the appropriate µOPs.

Die

Core Floorplan

Core Cluster Floorplan

References

• Burgess, Brad. "Samsung exynos M1 processor." Hot Chips 28 Symposium (HCS), 2016 IEEE. IEEE, 2016.