Microsoft has talked up its well-regarded virtual reality headset called HoloLens, but has been a little stingy on some technical details, such as what's powering the device.
However, it finally took the wraps off that mystery at an appropriate show. Microsoft detailed for the first time its custom CPU for HoloLens at Hot Chips, an annual semiconductor conference held at Stanford University every August.
Hot Chips is a great show, and I miss attending it even more than IDF, since a variety of chip vendors show up to talk. Between the extreme technical detail from Ph.D. engineers and some brutal accents, it requires your full attention, but that's not a hard thing to do because the insights are often fascinating.
At this year’s show, Microsoft revealed its Holographic Processing Unit (HPU) chip used in HoloLens. The HPU is a 24-core DSP design that uses Tensilica cores from Cadence. The chip uses 8MB of SRAM and a layer of 1GB of low-power DDR3 RAM, all packed into a 12mm-by-12mm BGA package.
Each DSP core is given a particular task to focus on, and the HPU can perform up to a trillion calculations per second and accelerates algorithms 200 times faster than pure software alone. It handles all of the environmental data, as well as aggregates data from sensors, and processes the wearer's gesture movements. There is a separate CPU, an Intel Atom x86 "Cherry Trail" system on chip (SOC), which has its own 1GB of RAM and runs Windows 10 and Windows apps.
The design of the HPU took several things into account: It had to be able to handle several different algorithms with varying maturity, math, branching and memory access patterns. To future-proof the device, the compute cores needed to be no more than 50 percent utilized. There had to be guaranteed latency and duty cycle requirements on processing, and no one-size-fits-all solution was considered. Microsoft considered SOC CPUs/GPUs, arrays of traditional CPUs and commercial ISPs before going with the Cadence design.
Between Surface, Xbox, Kinect and HoloLens, Microsoft has become a major force in hardware engineering, and, more important, it is bringing technology previously thought unaffordable to the mass market. Shame about those smartphones, though.
The HoloLens began shipping to developers in March, and earlier this month it began shipping to business customers and developers for a whopping $3,000. It still does not have a consumer release date.