AH TechTalk: Snapdragon 810 Has Last Laugh Against Samsung

The Qualcomm Snapdragon 810 has received a lot of attention recently and unfortunately, not all has been positive. As a recap, the Snapdragon 810 is Qualcomm's current flagship System-on-Chip. It pairs a quad-core ARM Cortex-A53 processor with a quad-core ARM Cortex-A57 processor in a reasonably conventional layout. The A53 cores may be clocked at up to 1.6 GHz and the ARM Cortex-A57 core can reach up to 2.1 GHz. The 810 includes the Adreno 430 GPU for high-end video performance, too, however the Snapdragon 810's troubles are not related to performance but instead to the heat output of the processor. When the Snapdragon 810 was not yet in production but instead was being previewed, its performance was measured in Qualcomm's reference hardware. By reference hardware, this is usually a smartphone or tablet design picked as being comparable to possible models that might contain the new processor. At this time, the Snapdragon 810 was shown to have comparable performance to what we knew about the up-and-coming Samsung Exynos 7420 processor. And given that both processors are essentially made from very similar components (the Exynos 7420 has a quad core Cortex-A53 chip paired up with a quad core Cortex-A57 at similar clock speeds), this was no surprise.

However, production smartphones featuring the Snapdragon 810 are being reported as "overheating," somewhat sensationally by the source website, which is written very much from a Samsung perspective. Yes; Samsung did not use the Qualcomm Snapdragon 810 processor in the Galaxy S6 but instead opted for an in-house chip, the Exynos 7420. And the key difference between the Snapdragon 810 and the Exynos 7420? That the Qualcomm chip is built on a 20nm die size and the Exynos on a 14nm die size. The smaller the die size, the smaller the chip and the less voltage that must be applied in order to drive the processor. Power consumption (and heat output) is proportional to the square of the voltage applied, which means that a small drop in voltage (such as dropping from 20nm to 14nm die size) can have a disproportionately large impact on power consumption and waste heat).

This means that in the real world, the small, cramped space of a modern smartphone is not the ideal home for the high performance Qualcomm chip. As the processor temperature rises, so the higher powered processor cores are shut down in order to keep the heat output low. This means that when put under sustained load, devices powered by the 810 show reduced performance; they are thermally limited. If a chip is overheating, in other words if the device is uncomfortably hot when used, then this may be adjusted by lowering the thermal limits and so running the processor cooler and slower. We've already seen HTC update the One M9's software with what appears to be a tweak in how the processor handles individual cores and their clock speeds. Sony appear to be working on a similar fix for the Xperia Z3+ and Z4 devices.

Samsung's Exynos 7420 is as fabulous a processor as the Qualcomm Snapdragon 810, but it happens to be built on a smaller die size and so produces less heat. However, there is a very important consideration when it comes to die sizes: the smaller the die size, the harder the processor is to manufacturer and the more error-prone the process. This results in a lower yield, that is, the higher the proportion of faulty processors following manufacturing. The lower the yield, the more expensive each processor is per unit, as those wasted processors must be paid for. We've seen rumors that Samsung's brand new 14nm manufacturing process has been less than perfect. Perhaps this is why no other manufacturer has (yet) been able to buy the Exynos 7420 System-on-Chip for use in its own handsets - and this is an important point.

Unfortunately, Qualcomm's public relations department have perhaps let the side down here. We have written about Qualcomm's announcement claiming that the overheating issues were caused by pre-production SoCs, revision 1 units. The version used in production handsets is revision 2, but we've seen a number of devices launching with revision 2.1, which has a number of subtle changes (including the GPU clock speed is raised by 30 MHz to 630 MHz and there have been some memory management improvements). What we are unsure about is how much heat the reference design is able to remove from the processor and what the manufacturers' component specifications state is the thermal output of the 810. Did Qualcomm underestimate the 810's TDP (thermal design power)? The TDP shows a smartphone designer the amount of heat the chassis will need to dissipate under normal operations; if the processor produces more heat than the chassis was designed to cope with, then the processor will run hot. If matters are this simple, either Qualcomm underestimated the Snapdragon 810's TDP or smartphone engineers have provided inadequate cooling for the processor. The Sony Xperia Z4 Tablet, powered by the Snapdragon 810, appears to have less of a cooling issue but then the tablet chassis has more space available for cooling.

However, if Samsung aren't making their Exynos 7420 processor available to the rest of the market, but the Snapdragon 810 may be tuned through software control, those manufacturers with a smartphone powered by the Qualcomm flagship processor did not have much in the way of a choice. Samsung's jump to the 14nm die size is going to help sell the Galaxy S6, but until they start selling the 7420's manufacturing process to other manufacturers, Qualcomm may still have the market sewn up.

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