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We've known for a long time that Microsoft'southward HoloLens relied on a custom "HPU," or Holographic Processing Unit, to provide the headset's mixed-reality mode and augmented reality capabilities. At Hot Fries this week, the company really released some details on how the flake works and what information technology's capable of.

Co-ordinate to Microsoft, the HPU can handle a trillion pixel operations per 2nd. While a diversity of designs were floated, including a partnership with Movidius, Microsoft ultimately went with a custom design that packs 24 Tensilica DSP cores and 8MB of enshroud into a single package, aslope 1GB of DDR3. The cores were customized with additional instructions (EETimes reports 300 new instructions, while The Register claims 10). "We used programmable elements wherever possible and fixed function hardware where nosotros needed information technology to see our performance goals." Nick Baker, a technologist at Microsoft, told Hot Chips. "Nosotros took co-blueprint to an farthermost with this project."

HoloLens-HPU-die-plot

Image by EETimes

The scrap is designed to process feedback from the HoloLens' multiple cameras and process it in real time, and shares processing duties with a 14nm Intel Cherry-red Trail Cantlet SoC. With Intel having discontinued its Atom tablet and smartphone processors it'southward not clear what'due south side by side for HoloLens, and Microsoft hasn't commented on whether it volition develop a second-generation HPU or bring the hardware to market at a lower price betoken more than suitable for the consumer and corporate market. Ability consumption for the HPU is also reported differently, with EETimes claiming the chip operates "in a ability budget lower than the 4W Intel Atom-based Cherry Trail SoC that acts as its host processor," while The Annals states "The HPU draws less than 10W and includes PCIe and standard serial interfaces."

At present, the HPU operates at less than 50% of its maximum theoretical capacity. While this undoubtedly keeps power consumption down, it likewise gives Microsoft a way to extend its pattern and brand more use of it in the future without building a make-new fleck. The current HPU is built on 28nm technology at TSMC, which ways a dice-compress to 14nm could besides amend power consumption and battery life (or allow the bit to leverage more of its processing capabilities in a hereafter product).

Microsoft's slides imply that the data sent to the Cherry-red Trail SoC is extensively processed to minimize information transfer requirements and power consumption. The company evaluated a number of potential solutions earlier settling on the DSPs, including sharing a workload across both CPU and GPU and using an array of traditional CPU cores. The available slides suggest that power consumption remains a formidable barrier to making AR work in clothing headsets — time to come designs will probable focus on minimizing ability consumption for both AR and VR. On the other paw, gamers take clamored for higher-resolution displays and larger viewing frustums — and these are the kind of features that tend to increase weight and ability draw, not reduce it.

Based on what Microsoft has revealed about HoloLens' HPU, information technology's clear that the existing solution has some legs — but without knowing more well-nigh Redmond's long-term plans, we tin't say if we'll ever see the hardware in consumer toll points. Right now, HoloLens is a $3,000 solution and marketed to developers only.