This week during the Hot Chips engineering conference at the Stanford Memorial Auditorium, Microsoft chip architect John Sell introduced the world to the secretive APU the company jointly developed with AMD. As it turns out, the APU is rather enormous, featuring a 363 square millimeter surface manufactured with TSMC's 28 nm HPM process technology. As a comparison, Intel's 22 nm Core i7-4770K "Haswell" chip measures 177 square millimeters.
Naturally the larger the chip becomes, the more prone it is to forming small defects on the wafer surface that could result in a repeat of the Xbox 360 "Red Ring of Death" fiasco. To generate better yields for the Xbox One generation, Microsoft reportedly designed redundancies into the chip so that if one portion becomes inoperable, the whole chip isn't totally worthless.
Sell also revealed that the chip packs 5 billion transistors that combines the CPU cores, the GPU core, 47 MB of cache and 32 MB of extra on-chip storage. He said the cache/storage aspect uses up about half of the chip's transistors, and because storage is embedded into the APU, the chip saves power because it doesn't need to constantly access the console's 8 GB of DDR 3 RAM or the 500 GB hard drive.
Sell didn't disclose just how much this chip will consume, but said that it will be power gated down to 2.5 percent. The company actually designed small islands and gates within the APU that switches off specific areas so the chip can consume less power when needed.
As previously reported, the APU has eight AMD Jaguar 64-bit CPU cores with 32 KB of instruction and data cache. Four cores will be connected to 2 MB of shared Level 2 cache along with the embedded a graphics DirectX 11.1+ core. AMD revealed this hUMA technology back in April, or rather its Heterogeneous Uniform Memory Access tech that builds upon the Heterogeneous Systems Architecture (HSA).
Essentially shared memory makes life easier for developers and provides overall improved system performance. AMD's Kaveri APUs were the first to take advantage of this tech, and the PlayStation 4 naturally also makes use of this technology given its based on an AMD APU as well.
Getting back to the Xbox One's chip, the GPU portion of the APU will reportedly be accompanied by 15 special purpose processors including four command processors (two compute, two graphics), and two dedicated vector cores for the audio subsystem. The data highways can transfer bits up to 204 GB/s across different parts of the chip, and up to 68 GB/s to the off-chip DDR3 memory.
In addition to the Xbox One's APU, Microsoft system designer Patrick O’Connor took the stage to talk about the new Kinect's processor and light sensor. The team wanted the sensor to have enough intelligence to distinguish the player from objects in the surrounding area including the couch, the lamp and so on. Thus the device can pinpoint each player less than 3.3 feet away and more than 6.6 feet away using a 70 degree field of view.
O'Connor explained that Kinect "illuminates" the room with its own modulated light, and uses the 512 x 424 sensor to see that reflected light, which will be out of phase depending on how that light is reflected off objects. The console then processes the info to weed out ambient light and to define the actual "active" image. O'Connor said that Kinect supports up to six simultaneous players, but determining who is actually playing takes some processing power.