AMD’s 2016 APUs to be powered by ‘Excavator’ x86 cores – slides

Advanced Micro Devices will not use its next-generation high-performance “Zen” micro-architecture for its accelerated processing units next year, if excerpts from an alleged AMD presentation published by a web-site are to be believed. While the slides reveal AMD’s intentions, they do not answer all the questions about the forthcoming chip.

“Bristol Ridge”: “Zen” or “Excavator” cores?

AMD’s code-named “Bristol Ridge” APU due in 2016 will rely on “Excavator” cores and “Carrizo” design with minimum changes, based on slides published by BenchLife. The presentation published by the web-site was allegedly demonstrated to AMD’s partners on the 27th of March, 2015. The presentation is fairly detailed when it comes to technical information about “Bristol Ridge” and AMD’s next-generation APU platform. However, the presentation contains a number of typos, which may indicate that the web-site has obtained a preliminary version of the document*.

The first rumours about “Excavator” cores inside “Bristol Ridge” emerged in January, which means that the document does not contradict the previously released information. However, in May, a slide from another AMD presentation (which was allegedly a preliminary presentation for the company’s financial analysts day) revealed that “Bristol Ridge” was to be based on up to four “Zen” cores.

Unfortunately, the presentation published by the Chinese web-site does not contain any proper release milestones schedule for “Bristol Ridge”, but only says that the new APU will hit the market in July, 2016. Typically, when a semiconductor company is working on a project, it sets milestones for it. There are target timeframes for tape-out, availability of engineering samples, mass production start and so on. If the milestones are not listed, it may mean that either the company’s plans are not solid or the company has issues with execution.

Since slides about “Bristol Ridge” published by two different sources contradict each other, it may mean that either AMD is choosing between options regarding its next-gen desktop APUs, or the information about “Zen”-based APUs in 2016 is fake. To release “Bristol Ridge” featuring “Carrizo” architecture and “Excavator” cores, AMD needs to improve clock-rate potential of its latest APU. To launch a brand-new accelerated processing unit featuring “Excavator” cores, AMD will have to design an all-new chip from the ground up. Based on what we know about “Zen” from unofficial sources, the new APUs and CPUs will feature a layout that will be completely different when compared to today’s processors.

“Bristol Ridge”: “Carrizo” for desktops

Just like AMD’s current-gen mobile APU, the “Bristol Ridge” will integrate a basic input-output controller, which supports USB 3.0, PCI Express 3.0 x8 to connect to GPUs, PCI Express 3.0 x4 to connect to code-named “Promontory” core-logic sets, PCI Express 3.0 x2 with Serial ATA support to connect to HDDs and SSDs as well as SD, SPI, eSPI and I2S interfaces. The chip is expected to use AM4 form-factor previously known as FM3 (as the document names it). While the APU resembles “Carrizo”, it will come either in pin grid array (PGA) or land grid array (LGA) form-factor. Moreover, “Carrizo” has more advanced I/O capabilities.

AMD’s “Bristol Ridge” accelerated processing unit will integrate four “Excavator” (XV) cores (two dual-core modules) with 2MB of L2 cache (1MB of cache per module, 512KB per core), AMD Radeon graphics processor with eight compute units (512 stream processors) based on the GCN 1.2 instruction set architecture, a dual-channel DDR4 memory controller, a special high-performance bus to connect x86 cores to graphics cores and DRAM as well as heterogeneous system architecture features (compatible with the HSA 1.0 specifications).

Multimedia, security and input/output capabilities of “Bristol Ridge” will remain unchanged from “Carrizo”. The APU will feature universal video decoder 6.0 (UVD6) with HEVC decoding support for ultra-high-definition (UHD) video, video encoder engine 3.1 (VCE3.1) and audio co-processor 2 (ACP2). In addition to TrustZone technology, AMD’s new chip will also support TPM 2.0, crypto acceleration and secure boot.

The upcoming desktop APU from AMD will support HDMI 2.0 output, which means it will be able to display 3840*2160 video with 120Hz refresh rate, stereo-3D UHD video and so on. The APU will support up to three displays.

Just like “Carrizo”, “Bristol Ridge” will also feature advanced power management capabilities, including connected standby, adaptive voltage and frequency scaling (AVFS), clock stretcher, STAPM and so on.

“Bristol Ridge”: “Carrizo” on steroids?

Without any doubts, “Bristol Ridge” in the form described by the document is a derivative from “Carrizo”. The only question is whether the chip is actually a re-badged “Carrizo”, or a new APU tailored to work at higher clock-rates.

AMD claims that “Carrizo” was designed to be extremely energy-efficient and highly integrated, but was not developed to operate at extreme clock-rates. To maximize transistor density (integration) and lower power consumption, AMD used high-density chip design libraries (HDL) for the chip. According to the company, usage of high density libraries and automated design methods (akin to those used for graphics processing units) helped the company to reduce sizes of “Excavator” cores by 23 per cent compared to “Steamroller” cores inside “Kaveri” and reduce their power consumption by whopping 40 per cent.

When CPU makers design microprocessors that should operate at high clock-rates, they use high-performance chip design libraries, which decreases transistor density and makes chips bigger (and costlier). The companies then adjust their designs in a bid to optimize sizes, frequencies and power consumption. In general, high-performance chips differ from low-power chips, even though that difference may be negligible in some cases.

While “Carrizo” is not supposed to run at high frequencies, maximum clock-rate of such chips is actually 3.40GHz (which may or may not be enabled by a particular PC maker due to TDP limitations).

According to a slide published by BenchLife, “Excavator” cores inside “Bristol Ridge” will operate at ~4GHz clock-rates, which is a significant improvement over “Carrizo”. Theoretically, it may indicate that the “Bristol Ridge” is a new chip that was partly re-designed using high-performance libraries. Thanks to higher clock-rates and 10 per cent higher IPC [instructions per clock] performance of “Excavator” vs. “Steamroller”, expect “Bristol Ridge” to be faster than “Kaveri” in general-purpose applications.

The upcoming APU will also support DDR4 memory, which may mean that the chip is different from “Carrizo”. While this is possible, it may also demonstrate that “Carrizo” also technically supports DDR4, but it is not enabled due to power consumption or cost concerns.

Thanks to higher clock-rates and DDR4 support, graphics processing performance of “Bristol Ridge” should be higher compared to that of “Kaveri”.

The “Bristol Ridge” chip is expected to be made using an unknown 28nm fabrication process and will have up to 95W thermal design power. By contrast, “Carrizo” has maximum TDP of 35W.

Final words

AMD’s “Bristol Ridge” accelerated processing units will offer considerably higher performance than “Carrizo” thanks to higher frequencies, improved memory bandwidth and other optimizations. Moreover, the new APUs will also be faster than “Kaveri”. However, do not expect any breakthroughs from “Excavator”. The “Bulldozer” architecture is clearly outdated and AMD decided not to invest a lot in its enhancement. In fact, AMD also did not improve its integrated graphics processor anyhow compared to “Kaveri”.

If “Bristol Ridge” products arrive in the third quarter of 2016, they will face tough competition from Intel’s “Skylake” processors. Being made using more advanced process technology and featuring new micro-architectures for both general-purpose and graphics-processing cores, the new chips from Intel promise to offer high performance in all types of applications.

AMD did not comment on the news-story.

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KitGuru Says: Re-introducing “Carrizo” for desktops next year is hardly something that AMD management wants. It is obvious that the chip will be slower compared to Intel’s offerings in many, if not all, applications. The only reason why AMD may plan to introduce “Bristol Ridge” with “Excavator” cores is because its “Zen”-based APUs are not ready and AMD just cannot sell “Kaveri” for three years.

While the prospects of “Bristol Ridge” do not look exactly good, keep in mind that the information comes from unofficial sources and next year AMD may introduce something completely different.

*Note: The images originally published by BenchLife have been altered for better viewing experience.

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