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Around the globe, businesses and governments are seeking ways to mitigate the rapidly increasing energy consumption of data centers.
Nowhere is the issue more urgent than Japan, which aims to achieve carbon neutrality by 2050. The ambitious national commitment is driving innovation across industries, including the development of next-generation “green” data centers — facilities that combine high performance with high energy efficiency.
Fujitsu is playing a vital role in these transformative efforts. The global technology giant has been at the forefront of advanced processor development for 60 years, and in response to its home country’s 2050 carbon-neutral goal, Fujitsu is participating in a national project to develop new, more sustainable data centers.
The project’s goal: 40% energy savings compared to current data centers, while maintaining the large capacity and compactness required to handle explosive increases in data volume.
To succeed, Fujitsu knew incremental improvements wouldn’t be enough. Maximizing energy efficiency without sacrificing performance demanded a bold leap forward with a new processor architecture designed from the ground up.
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Optimized balance
Fujitsu’s answer is its FUJITSU-MONAKA processor. This highly power-efficient chip (named for a Japanese sweet made of azuki bean paste and crisp mochi wafers) marks a significant step toward greener data centers and achieving the national project’s goal of 40% energy savings.
FUJITSU-MONAKA’s innovative design carefully optimizes how its components deliver speed and reliability while keeping energy use in check. It features a 3D many-core architecture, integrating three distinct units: a core die with Arm cores, an SRAM die for last-level cache, and an I/O die supporting DDR, PCI Express Gen6, and more. The core die leverages a 2 nm process to deliver exceptional performance and low power consumption, while the SRAM and I/O dies use a 5 nm process to optimize cost and efficiency.
“By selecting the optimal process for each die, we achieve both low cost and high performance with low power consumption,” says Nobuyuki Matsui, processor development manager at Fujitsu.
FUJITSU-MONAKA is based on the Armv9 architecture and features Fujitsu’s own custom microarchitecture, both of which are optimized for state-of-the-art Arm server systems.
Fujitsu processor development manager Nobuyuki Matsui at Synopsys User Group (SNUG) Japan 2025
Ready for Arm
A non-negotiable factor of developing FUJITSU-MONAKA was compliance with Arm SystemReady. This rigorous testing program guarantees compatibility and reliability across the Arm ecosystem that powers countless devices worldwide, ensuring customers don’t encounter unexpected hardware or software issues.
But compliance with SystemReady is no simple box-checking exercise. In recent years, several Arm server designs have encountered SystemReady violations only after silicon is already manufactured. Fujitsu needed to avoid this nightmare scenario.
“In SoC [system-on-chip] development using cutting-edge processes, the cost and impact of a respin are significant,” says Matsui. “It is increasingly important to catch issues in the pre-silicon phase.”
To address these risks early, Fujitsu needed to run exhaustive tests using Arm’s Architecture Compliance Suite (ACS) packages. These tests require extremely long RTL simulations with tens of billions of cycles, as well as a dedicated software environment for simulating PCI Express devices and increasing test coverage.
Pre-silicon emulation with ZeBu
Fujitsu turned to Synopsys ZeBu Server 5, a high-speed hardware emulator, to engineer a sophisticated emulation environment.
“For efficient verification, the stability of the test environment is crucial,” says Matsui. “We created a ZeBu Server 5 emulation model connecting the exerciser as a virtual device, prepared firmware with the exerciser driver, and built the ACS execution software environment.”
- A virtual system adapter (VSA) was used to flexibly switch virtual devices at runtime, enabling comprehensive ACS execution and OS boot testing without recompilation.
- Multiple PCI Express exercisers were connected to maximize test coverage.
- Custom firmware environments supported both bare-metal and UEFI testing.
- A proprietary system-level architecture simulator also contributed to “shift-left” verification.
“By checking with the architecture simulator before hardware emulation, we could detect issues earlier,” says Matsui.
His team also equipped simulation models with advanced debugging tools, including instruction execution traces, long-term software analysis, and PCI Express transaction monitoring. ZeBu Server 5’s high-speed waveform acquisition features further enabled rapid debugging.
Testing FUJITSU-MONAKA required long ACS runs — more than 130 billion cycles in all, and nearly 60 hours of simulation — and ZeBu Server 5 save/restore functions allowed Matsui’s team to pause, resume, and troubleshoot tests as needed without losing progress.
“With ZeBu Server 5, we could save not only the emulator state, but also the state of virtual devices running on the emulation host,” says Matsui. “Using save/restore functions, we improved debugging efficiency.”
Charting the future of sustainable data centers
In the end, the FUJITSU-MONAKA processor passed the Arm SystemReady pre-silicon tests, ensuring compatibility with the global Arm ecosystem. It was a key moment in the processor’s development, and Matsui credits Fujitsu’s collaboration with Synopsys and use of ZeBu Server 5 for making it possible.
“By conducting ACS pre-silicon tests, we achieved improved verification coverage,” he says. “We performed long simulations and debugging, detected and investigated system specification and hardware logic issues, and confirmed SystemReady compliance in the pre-silicon phase, completing tape-out.”
The early detection saved valuable time and resources — but just as importantly, it provided confidence that FUJITSU-MONAKA will ultimately deliver on its promise of energy efficiency and reliability.
Set for release in 2027, FUJITSU-MONAKA marks a milestone in Japan’s journey toward carbon-neutrality. By leveraging advanced architecture, rigorous pre-silicon verification, and strategic partnerships with technology leaders like Synopsys, Fujitsu is redefining what’s possible for green data centers.
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