Samsung is an electronics powerhouse that has its fingers in virtually every segment of the market. It only makes sense that a company with resources like that would develop its own hardware to power many of its devices, and that’s why Samsung began producing its own custom ARM system-on-a-chip (SoC) called Exynos back in 2010. Samsung has just announced an updated version of the Exynos 5 Octa with a new GPU, and hopefully some bug fixes.
The first eight-core Exynos was known internally as the 5410, whereas this new chip is the Exynos 5 Octa 5420. The similarity in model numbers should tell you that the two share a lot of features. Both SoCs come with four ARM Cortex-A15 processing cores, and four Cortex-A7 cores. Samsung uses ARM’s big.LITTLE design to share the workload between the faster A15 cores, and the slower, more efficient A7s.
The 5420 bumps the clock speed of the application processors a little bit. The A15 goes from 1.6GHz to 1.8GHz. The smaller A7 cores are now running at 1.3GHz, up from 1.2GHz. Samsung claims the raw processing power of the new Exynos has been boosted by 20 per cent.
The big.LITTLE configuration is designed to allow seamless switching between high power cores and more efficient ones to improve battery life. The first Exynos 5 Octa used a specific implementation of big.LITTLE called Cluster Migration. That means either the A15 cores or the A7s are active, but never a mix of the two. Maybe it’s not fair to call it an eight-core chip, but the Samsung marketing machine cannot be stopped.
Samsung talked up the Exynos 5 Octa quite a lot when it was announced, but the SoC never saw wide scale use beyond the international Galaxy S4. Part of the reason is that the Exynos is hard to manufacture, but there was also a troublesome bug in the CCI-400 coherent bus interface. Developers noticed the bizarre behaviour caused by this issue, and Samsung was eventually forced to admit that coherence between the two CPU islands was disabled on the 5410. Basically, switching between the A15 and A7 cores caused all caches to be flushed from memory. That’s trouble on both the performance and battery life fronts – both of which big.LITTLE is supposed to improve.
Samsung doesn’t like to talk about the coherency bug, so there’s no word on whether or not it’s been fixed in the 5420, but it probably is. Otherwise, why release a new Exynos 5 Octa running Cluster Migration so soon after the last?
Moving beyond past mistakes, Samsung is also hoping to amp up graphical performance with the new Exynos. The 5420 includes an ARM Mali-T628 MP6 GPU, which is a departure from the PowerVR SGX544MP3 used in the 5410. This is actually Samsung coming home to Mali, which it has traditionally used – the PowerVR in the 5410 was the outlier. The Mali-T628 in this version of the Exynos is in a six-core configuration, which no other part has.
Samsung’s numbers indicate the Mali-T628 GPU in the Exynos 5420 offers double the performance of the PowerVR from the 5410. If that’s even close to accurate, it would put Samsung far out ahead of the most recent iPad in terms of graphical prowess.
Beefing up the GPU is a good thing, but the Exynos 5 Octa 5420 feels like a do-over for Samsung – an opportunity to fix that embarrassing coherence bug. Future versions of the Exynos could move beyond Cluster Migration altogether and implement one of the more interesting big.LITTLE configurations like big.LITTLE MP, which allows all cores to be active for intelligent scheduling. That would be better placed to compete with Qualcomm chips, which can dynamically enable cores as needed.
The new Exynos is set to go into production in August, so it could hit devices later this year. Perhaps we’ll see it in the Galaxy Note 3? (Although previous rumours have indicated otherwise).
You might also want to read: Cortex-A12 and Mali-T622: The mid-range power that ARM was missing.