What am I looking at?
Well, the first thing to note is that we're looking at something very different from a standard R700 die (we know that Latte is based on AMD's R700 line originally). This makes it more difficult than we'd hoped to analyse, as comparison to existing AMD die shots would generally be our main strategy. There are a few things we can say so far, though:
- The die is exactly 11.88 x 12.33mm (146.48mm²)
- The large orange block on the left is the 32MB of eDRAM (MEM1).
Up: It's 40.72mm², and takes up 27.8% of the die.
- The smaller orange block above it seems to be about 3MB of eDRAM (
Up: It's 4.25mm²). This might be the framebuffer for Wii mode, or the L2 texture cache, or something else, we're not 100% sure at this point.
- In the lower left there is what appears to be a dual-core ARM (used for security/streaming purposes) and possibly a DSP (or custom logic for the video streaming).
- Along the bottom and right sides of the chip are likely DDR3 controllers. The top and left sides of the chip are probably for communication with the CPU.
- All the small dark orange/black blocks you see over the GPU part of the die are SRAM blocks. The number and formation of them should give us clues as to what part of the chip does what.
- The eight squarish groupings on the right hand side are possibly the VLIW5 shader clusters. However, due to the apparent increased amount of SRAM there, along with the unusual layout and the general changes to the die, it's entirely possible that the number of shaders in each cluster has changed from R700 dies. In fact, at this point it's even possible that the microarchitecture itself has changed, a la the VLIW4 used in some of AMD's 6000 series GPUs. Therefore, we could have a fairly unusual number of shader cores.
- It's likely there's some legacy Broadway hardware on there for BC purposes.
Up: To clarify, Wii's "Broadway" GPU (inc. eDRAM) was 8mm x 9mm, or 72mm² on a 90nm process. That would only account for about 10-20% of the die space on a 146.48mm² 40nm chip, if they just slapped Broadway on there. However, given
Shiota's comment here, many of the Wii BC functions should actually be handled by the Wii U's GPU hardware, so the actual amount of die space used purely for Wii BC should be very small, possibly just 5-10%.
I'll be updating this post as more info is figured out, so check back for updates.