Monday, September 24, 2012
Playstation 4 technical speculations
Playstation 4 uses AMD chips based on the A8-3859 APU (accelerated processing unit) and Radeon HD 7670 GPU GPU supports HDMI1.4a Inside sources have leaked information to the press claiming that the CPU in the next-generation PS4 (codenamed Orbis) is an AMD Llano A8-3850. The chip will supposedly be paired with an AMD Radeon 7670 GPU with 1GB of integrated VRAM. With all due respect to IGN, this is the sort of report that deserves a considerably better review than they apparently gave it. Sony may well be working with that level of AMD hardware, but that's not the same as shipping said configurations. Let's start with the APU. The A8-3850 was one of AMD's earliest Llano chips; a 100W 2.9GHz quad-core with an integrated Radeon 6550D. It didn't ship in high quantity -- AMD chose to emphasize shipping out mobile Llano's rather than their desktop counterparts. Llano is a much stronger mobile chip than it is on the desktop; AMD has been unable to scale the chip to higher clock speeds (think 3GHz+) without dramatically increasing its TDP. Llano's Achilles heel is the interconnect between its CPU and GPU; the communication channel is very similar to an old-school motherboard northbridge implementation. It's easy for the CPU to transfer data to the GPU but much more difficult for the GPU to do the same -- which means it's also much harder for AMD to take advantage of Llano's array of GPU cores as a general-purpose compute array. Bandwidth is quite limited; Llano's GPU is critically dependent on main memory bandwidth to function well. Now, let's talk about the Radeon 7670. It's a rebranded HD 6760, based on the budget Turks 40nm GPU. According to IGN, "When the APU is paired with the HD 7670, however, Sony will be able to utilize an asymmetrical CrossFire configuration to share the load of realtime graphics processing." That's technically true, but the benefits of Hybrid Crossfire are limited to DX10/11 games (it's unclear how AMD would scale the benefit to OpenGL and older DX9 titles are often slower than they'd be with just the dGPU.) Scaling benefits are also erratic and vary significantly from game to game. The reason we don't believe reports that Sony would adopt the Llano+6760 is that AMD has much better hardware either already shipping or coming in the very near future -- certainly well before the PS4's launch date. Llano may have done a great job getting AMD's foot in the door, but the chip is based on AMD's four-year-old Shanghai CPU. AMD has no plans to continue building Llano at nodes below 32nm, and console manufacturers always plan to scale a CPU through multiple process nodes. The current PS3 is produced on a 45nm/40nm process, having begun life at 90nm. If Llano's GPU was good, Trinity's is expected to be significantly better. More importantly, its GPU is based on Cayman, which means it's a substantial improvement over the HD 5000-era part baked into Llano. Similarly, AMD might well target a budget price point for whatever GPU the PS4 eventually uses, but it probably won't be derived from a graphics architecture that'll already be three years old by the time the system ships.