There were a number of threads I did not have time nor space to fully pursue in my recent EETimes article (“the article”) on the A5_3. The first was the question: was the Apple TV overpowered with the A5_2? The short answer is yes. The long answer leads into the second question: for what was the A5_2 designed?
As noted in the article both the CPU and GPU received a haircut in A5_3. The CPU was reduced by removing one whole core and some cache from the remaining core. The GPU was also reduced by more than 50%. As was argued in the article the size of the two-core GPU remained relatively constant, for the first A5 and the A5_2. In making this assertion the GPU, or more generally video dedicated circuitry, of the A5_2 was identified as a cluster of eight blocks. Four of these blocks are seen on the A5_3. If in fact the GPU was represented by the single block identified by Chipworks then the haircut would have been all that much shorter based on the GPU size of the original A5. It is also worth noting that while the die area for the GPU remained relatively constant from the A5 to A5_2, the actual blocks and layout appeared quite different. Further, there were three fewer digital blocks on the A5_3 compared to the A5_2. So, even if you accept the Single v. Double Core marketing there was a reduction on CPU cache, GPU size and the number of digital blocks in the A5_3. One thus arrives at the short answer. The A5_2 was overpowered for the Apple TV.
Now the second question. For what was the the A5_2 actually designed? Since its introduction in the AppleTV the A5_2 went on to appear in the iPad mini and the 5th generation iPod touch. In spite of the Single v. Double Core marketing the actual design remained the same. At the moment the iPad and iPod in which the A5_2 finds itself provide similar computing requirements. They would run very similar applications, of course the same OS, and both require the ability to compute video for an essentially 1080 display and the a 1080P video camera. Two 1080 streams seem to fit nicely with the 8 blocks mentioned above, that have two fold symmetry. The Apple TV on the other hand does not require the two 1080P streams. So, the answer to our second question is that the A5_2 appears to have been designed from the get-go for the iPad mini and iPod Touch in which it now finds itself.
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