Revision as of 17:35, 17 March 2019

Mars I is the first many-core ARM SoC microarchitecture designed by Phytium Technology for the Chinese server market.

Process technology

Mars I is designed for TSMC's 28 nm process.

Architecture

• 64 ARM cores
• 28 nm process
• 2 GHz
• FTC-661/0 Xiaomi core
• System memory
  • DDR3
  • 1600 MT/s

This list is incomplete; you can help by expanding it.

Block diagram

Entire SoC

Panel

Core

Main article: Xiaomi Core

See Xiaomi Core.

Panel Architecture

Phytium organizes their processors using a grid-layout they call Panels they call Panel-based data affinity architecture. Each panel consists of 8 independent ARMv8-compatible cores. Phytium "Mars" processor consists of 8 such panels for a total of 64 cores. Panels are interconnected with a 2-dimensional mesh network-on-a-chip level 2 cache with 4 MiB per panel for a total of 32 MiB.

In addition to the main die, Mars uses an additional Cache & Memory chips (CMC) auxiliary chips. "Mars" uses 8 such chips connected to the main die providing 16 MiB of level 3 cache for a total of 128 MiB as well as 8 dual-channel DDR3-1600 memory controllers for a total maximum bandwidth of 204 GiB/s. Mars also provides two 16-lane PCIe 3.0 interfaces. The chips incorporates ECC and parity protection on all caches, tags, and TLBs.

Panel

Each Panel consists of 8 cores - each ARMv8-compatible, supporting AArch32 and AArch64 modes, Exception Levels EL0-EL3, as well as ASIMD-128 operations. Each core has its own inclusive L1 cache and a shared L2 cache (4 MiB per panel). Each panel contains two Directory Control Units (DCU) which are in charge of maintaining directory-based cache coherency and one routing cell for managing the inter-panel communication.

On TSMC's 28 nm process, a panel is 6,000 µm x 10,600 µm (63.6 mm²).

Cache & Memory Chip (CMC)

The solve the complexity involved in having more than eight memory controllers on a chip, Xiaomi uses a coupled auxiliary Cache & Memory Chip (CMC) to scale the bandwidth with computing power. In the case of Phytium "Mars" chip which contains 64 cores on 8 panels, eight CMC chips are used which provides 16 DDR3 controllers (8x2) along with 16 MiB of data L3 cache and 2 MiB of data ECC. Phytium proprietary interface is used between the processor and the CMC chip.

Memory access Latency(ns) Local L1 cache hit ~2 Local L2 cache hit ~8 Affinitive L2 cache hit ~20 Affinitive L3 cache hit ~36 Affinitive DDR access ~70

• Panel & NoC operates @ 2 GHz
• CMC operates @ 1.5 GHz

Interconnects & Hawk

Hawk is Pythium cache coherence protocol which implements a distributed directory-based global cache coherency across all the panels. Hawk is a MOESI-like package-based protocol. The network has a node on each panel called a Directory Control Unit (DCU) which is responsible for interfacing between the L2 caches in each panel to the CMCs (see § Panel Architecture). Phytium noted that it's optimized for exclusive atomic accesses.

Xiaomi implements a 2D concentrated mesh architecture on-die connecting each of the panels. Phytium "Mars" chip contains 8 panels which are organized in two rows of four panels each. Switching is relatively low latency with 3 cycles per hop. On average, packets will have around 9 cycles latency from any other panel. This network results in a bandwidth of 384 GiB/s each cell.

Destination Latency 0 3 1 6 2 9 3 12 4 15 5 12 6 9 7 6 Average 9

Die

SoC

• Mars is fabricated on TSMC's 28 nm process
• 10 metal layers
• ~180 million instances
• 639.576 mm² die size
• FCBGA Package
  • ~3000 pins
• 0.9 V_CORE, 1.8 V_IO
• 2 GHz, 120 W

Bibliography

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