The New Sleep States: S0ix

A bunch of PC makers got together and defined the various operating modes that ACPI PCs can be in. If everyone plays by the same rules there are no surprises, which is good for the entire ecosystem.

System level power states are denoted S0 - S5. Higher S-numbers indicate deeper levels of sleep. The table below helps define the states:

ACPI Sleeping State Definitions
Sleeping State Description
S0 Awake
S1 Low wake latency sleeping state. No system context is lost, hardware maintains all context.
S2 Similar to S1 but CPU and system cache context is lost
S3 All system context is lost except system memory (CPU, cache, chipset context all lost).
S4 Lowest power, longest wake latency supported by ACPI. Hardware platform has powered off all devices, platform context is maintained.
S5 Similar so S4 except OS doesn't save any context, requires complete boot upon wake.

S0 is an operational system, while S1/S2 are various levels of idle that are transparent to the end user. S3 is otherwise known as Suspend to RAM (STR), while S4 is commonly known as hibernate or Suspend to Disk (this one is less frequently abbreviated for some reason...).

These six sleeping states have served the PC well over the years. The addition of S3 gave us fast resume from sleep, something that's often exploited when you're on the go and need to quickly transition between using your notebook and carrying it around. The ultra mobile revolution however gave us a new requirement: the ability to transact data while in an otherwise deep sleep state.

Your smartphone and tablet both fetch emails, grab Twitter updates, receive messages and calls while in their sleep state. The prevalence of always-on wireless connectivity in these devices makes all of this easy, but the PC/smartphone/tablet convergence guarantees that if the PC doesn't adopt similar functionality it won't survive in the new world.

The solution is connected standby or active idle, a feature supported both by Haswell and Clovertrail as well as all of the currently shipping ARM based smartphones and tablets. Today, transitioning into S3 sleep is initiated by closing the lid on your notebook or telling the OS to go to sleep. In Haswell (and Clovertrail), Intel introduced a new S0ix active idle state (there are multiple active idle states, e.g. S0i1, S0i3). These states promise to deliver the same power consumption as S3 sleep, but with a quick enough wake up time to get back into full S0 should you need to do something with your device.

If these states sound familiar it's because Intel first told us about them with Moorestown:

In Moorestown it takes 1ms to get out of S0i1 and only 3ms to get out of S0i3. I would expect Haswell's wakeup latencies to be similar. From the standpoint of a traditional CPU design, even 1ms is an eternity, but if you think about it from the end user perspective a 1 - 3ms wakeup delay is hardly noticeable especially when access latency is dominated by so many other factors in the chain (e.g. the network).

What specifically happens in these active idle power states? In the past Intel focused on driving power down for all of the silicon it owned: the CPU, graphics core, chipset and even WiFi. In order to make active idle a reality, Intel's reach had to extend beyond the components it makes.

With Haswell U/ULT parts, Intel will actually go in and specify recommended components for the rest of the platform. I'm talking about everything from voltage regulators to random microcontrollers on the motherboard. Even more than actual component "suggestions", Intel will also list recommended firmwares for these components. Intel gave one example where an embedded controller on a motherboard was using 30 - 50mW of power. Through some simple firmware changes Intel was able to drop this particular controller's power consumption down to 5mW. It's not rocket science, but this is Intel's way of doing some of the work that its OEM partners should have been doing for the past decade. Apple has done some of this on its own (which is why OS X based notebooks still enjoy tangibly longer idle battery life than their Windows counterparts), but Intel will be offering this to many of its key OEM partners and in a significant way.

Intel's focus on everything else in the system extends beyond power consumption - it also needs to understand the latency tolerance of everything else in the system. The shift to active idle states is a new way of thinking. In the early days of client computing there was a real focus on allowing all off-CPU controllers to work autonomously. The result of years of evolution along those lines resulted in platforms where any and everything could transact data whenever it wanted to.

By knowing how latency tolerant all of the controllers and components in the system are, hardware and OS platform power management can begin to align traffic better. Rather than everyone transacting data whenever it's ready, all of the components in the system can begin to coalesce their transfers so that the system wakes up for a short period of time to do work then quickly return to sleep. The result is a system that's more frequently asleep with bursts of lots of activity rather than frequently kept awake by small transactions. The diagram below helps illustrate the potential power savings:

Windows 8 is pretty much a requirement to get the full benefits, although with the right drivers in place you'll see some improvement on Windows 7 as well. As most of these platform level power enhancements are targeted at 3rd generation Ultrabooks/tablets it's highly unlikely you'll see Windows 7 ship on any of them.

All of these platform level power optimizations really focus on components on the motherboard and shaving mWs here and there. There's still one major consumer of power budget that needs addressing as well: the display.

For years Intel has been talking about Panel Self Refresh (PSR) being the holy grail of improving notebook battery life. The concept is simple: even when what's on your display isn't changing (staring at text, looking at your desktop, etc...) the CPU and GPU still have to wake up to refresh the panel 60 times a second. The refresh process isn't incredibly power hungry but it's more wasteful than it needs to be given that no useful work is actually being done.

One solution is PSR. By including a little bit of DRAM on the panel itself, the display could store a copy of the frame buffer. In the event that nothing was changing on the screen, you could put the entire platform to sleep and refresh the panel by looping the same frame data stored in the panel's DRAM. The power savings would be tremendous as it'd allow your entire notebook/tablet/whatever to enter a virtual off state. You could get even more creative and start doing selective PSR where only parts of the display are updated and the rest remain in self-refresh mode (e.g. following a cursor, animating a live tile, etc...).

Display makers have been resistant to PSR because of the fact that they now have to increase their bill of materials cost by adding DRAM to the panel. The race to the bottom that we've seen in the LCD space made it unlikely that any of the panel vendors would be jumping at the opportunity to make their products more expensive. Intel believes that this time things will be different. Half of the Haswell ULT panel vendors will be enabled with Panel Self Refresh over eDP. That doesn't mean that we'll see PSR used in those machines, but it's hopefully a good indication.

Similar to what we've seen from Intel in the smartphone and tablet space, you can expect to see reference platforms built around Haswell to show OEMs exactly what they need to put down on a motherboard to deliver the sort of idle power consumption necessary to compete in the new world. It's not clear to me how Intel will enforce these guidelines, although it has a number of tools at its disposal - logo certification being the most obvious.

Platform Retargeting & Platform Power Other Power Savings & The Fourth Haswell
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  • Kepe - Friday, October 05, 2012 - link

    Let's see. I think we can agree that the Samsung Galaxy S III was the most important Android phone launch of the summer, so it should get comparable treatment if Anandtech was completely neutral. Let's compare the articles about the SGS III vs. iPhone 5

    Doing a search on anandtech.com gives us 8 articles/news posts about the SGS III vs. 13 articles/news posts about the iPhone 5.

    SGS 3:

    Five news stories about product announcements
    Performance Preview article
    Preview article
    Review article

    iPhone 5:

    Why iPhone 5 isn't launched in 2011 article
    Analyzing rumours about iPhone 5 article
    New SoC in iPhone 5 article
    iPhone 5 Live Blog from the product launch seremony
    Three news stories about new features and product announcements
    iPhone 5 Hands On article
    Lack of simultaneous voice and LTE/EVDO article
    Analyzing Geekbench results article
    Sunspider Performance Analysis article
    Performance Preview article
    iPhone 5 Display Thoroughly Analyzed article

    + The upcoming iPhone 5 Review article
    + articles such as "iOS6 Maps Thoroughly Investigated"

    Look at the difference. It's quite clear which device gets more coverage. And it's the same thing for older iPhones. Articles such as "Camping out for the new iPhone 3GS".

    This is NOT equal treatment of all products. This is why my trust for Anandtech has started to slip. Yes, Anandtech still is the best place for reviews, but one really has to wonder if those reviews still are as neutral and objective as they used to be.
    Reply
  • vFunct - Saturday, October 06, 2012 - link

    It's an android device. Android devices do not matter. Everyone uses iPhones anyways, They are better. Apple makes better products, including laptops.

    No need to waste space on Android.
    Reply
  • Haugenshero - Saturday, October 06, 2012 - link

    Please take your pointless apple fanboy drivel to another site that doesn't care about actual hardware and software and just like shiny things. Reply
  • cjl - Saturday, October 06, 2012 - link

    Apple's (iOS) current sales are only 20% of the overall smartphone market share, while Android is over 60%, so if either one of the two is largely irrelevant, it's apple. Reply
  • HisDivineOrder - Sunday, October 07, 2012 - link

    Shhhh, icks-nay on the facts-nay.

    You might cause a fanboy's head to explode near one of those inconveniently placed explosive barrels we walk by in real life.

    Just imagine a chain reaction. Caused by an Apple fan's mind being blown. You might take out an entire city block.

    Do you want that kind of devastation on your karma? Think different. ;)
    Reply
  • vFunct - Sunday, October 07, 2012 - link

    The Android market is the cheap giveaways.

    No one willingly pays money for an Android phone.

    Not everyone can afford the premium quality of an Apple product. They will have to settle for an inferior Android devices instead until they can afford higher quality products.
    Reply
  • Kepe - Monday, October 08, 2012 - link

    Nice trolling there. Now go back under the bridge and stay there =) Reply
  • Old_Fogie_Late_Bloomer - Tuesday, October 09, 2012 - link

    "Not everyone can afford the premium quality of an Apple product. They will have to settle for an inferior Android devices instead until they can afford higher quality products."

    Ha ha ha! Well done, if you're screwing around.

    But seriously, if you actually believe that, seek psychiatric help. :-P
    Reply
  • Spunjji - Thursday, October 18, 2012 - link

    Hahahahahahahahahahahahahahahahahahahahaha Reply
  • solipsism - Tuesday, October 09, 2012 - link

    And how many of the 20% is on one phone? Let me know when you figure out how to cover every single Androd-based device that hits the market in a given year. Reply

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