CNXSoft – Embedded Software Development

Yesterday, Linaro announced the released of the IKS (In-kernel switcher) implementation for big.LITTLE processor which allows the SoC to switch between individual Cortex A7 or Cortex A15 cores to optimize power consumption. Currently, the only consumer device using supporting big.LITTLE the Samsung Galaxy S4 thanks to Samsung Exynos 5 Octa featuring 4 ARM Cortex A7 and 4 ARM Cortex A15 cores. IKS implementation can only make use of 4 cores at a time in this processor, since it must choose between A7 or A15 depending on the load. HMP (Heteregenous Multi-Processing) implementation is currently worked on in order to be able to use all 8 cores, and distributes tasks to the right core for the job. You can read my previous post for differences between IKS and HMP.

Linaro explains the current source still needs a few more modifications before being upstream to mainline. The code was developed for and tested on the VExpress TC2 development platform, so if you want to try it on another big.LITTLE processor, an MCPM backend (Multi-cluster Power Management) and possibly a special cpufreq clock driver are required.

The switcher is comprised of 4 parts:

1. Low-level power management – Responsible for powering up and down individual CPUs, enabling and disabling caches, power planes, etc.
2. Switcher core – Handles the switching process itself, including the saving of the execution context for the outbound CPU, migration of interrupts from the outbound CPU to the inbound CPU, and restoration of the execution state on the inbound CPU.
3. The core cpufreq layer – Standard Linux cpufreq subsystem augmented with a special driver that provides an adaptation layer between that subsystem and the switcher core code described above.
4. The cpufreq policy governors -  Those are made of kernel modules or user space daemons monitoring the system activity and requesting CPU frequency changes to the cpufreq core.

You can get the IKS kernel with git:

git clone git://git.linaro.org/landing-teams/working/arm/kernel.git

It seems the most important part of the source code can be found in drivers/cpufreq/arm_big_little.c, arch/arm/common/bL_switcher.c, arch/arm/common/bL_entry.c, and arch/arm/common/bL_head.S.

b.L Code specific to TC2, more exactly Dual Cluster System Control Block (DCSCB),  can be found in arch/arm/mach-vexpress/dcscb.c and arch/arm/mach-vexpress/dcscb_setup.S. [Update: Based on the comment below,  TC2 code is actually located in arch/arm/mach-vexpress/tc2_pm.c, and arch/arm/mach-vexpress/tc2_pm_setup.S.]

You may want to refer to the following resources for further details about the implementation:

• Porting documentation
• Switcher code description (slightly out of date)

Linaro 13.04 has just been released. It features Linux Kernel 3.9-rc7 and Android 4.2.2.

A lot of work has been done on ARMv8 (Cortex A53) with further work on OpenEmbedded, more testing, and updates to the GCC toolchain. Calxeda EnergyCore server has been added to LAVA, Origen Quad now gets hardware video acceleration in Android Jelly Bean. Still more cleanup has been done on the kernel side with regards to Samsung and ST SoC, and a big.LITTLE porting guide is now available (linaro login required).

Here are the highlights of this release:

• LAVA
  
  • Prototype of a new publishing system is used to overcome performance problems with android-build.linaro.org.
  • Calxeda EnergyCore support is merged in LAVA, and an isolated system has been set up for web benchmarking.
  • Fedora support is merged in LAVA. A user can submit LAVA jobs using a Fedora pre-built image.
  • Boot commands are untangled from LAVA dispatcher. They’re now read from images.
  • Nexus implementation in LAVA is generalized and reusable for other devices that support fastboot/adb.
  • Linaro Image Tools 2013.04 released
  • More xml-rpc APIs available in lava dashboard to make life easy.
  • Test Definitions now available in lava dashboard. Accumulation of meta-data via test definitions started.
• Builds and Baselines
  • Dalvik VM unit test has been automated.
  • Accelerated video playback support on Android was added for Origen Quad.
  • Skia and 0xbench tests were added into lava-test-shell.
  • Test suite builder has been set up to provide test suite binaries as an overlay for Android.
  • Toolchain integration
    • Native toolchain on Android updated to 4.8.
    • Binaries for GCC 4.7 and 4.8 based toolchains released.
    • Android tree updated to compile with 4.8 based toolchains, all related changes upstreamed.
  • ARMv7 KVM enabled kernels and images are daily built and tested in Linaro’s CI loop.
  • OpenEmbedded ARMv8 engineering build provides 64bit HipHop VM requirements for porting and optimization purposes.
  • OpenEmbedded test cases (https://wiki.linaro.org/Platform/QA/TestCases/OpenEmbedded) have been automated. See https://git.linaro.org/gitweb?p=qa/test-definitions.git;a=tree;f=openembedded for current list.
  • Linux Linaro 3.9 2013.04 released
    • updated Versatile Express patches from ARM LT
    • updated arndale/exynos patches from Samsung LT
    • a patch to enable perf in Android by Bernhard Rosenkraenzer
    • vexpress64 support (both RTSM and Foundation model)
    • panda-fix-usb topic to make USB and on-board Ethernet to work on Panda with Device Tree enabled (cherry-pick / forward port of some of the dev.omapzoom.org commits)
    • a few fixes for MMC on Snowball from STE Landing Team
    • patch from ARM LT to fix lockups/crashes seen when enabling function tracer on TC2 with the not yet mainlined cpuidle driver
  • New or updated packages available from Linaro’s Overlay PPA: edk2-uefi, gator-daemon, gator, openssl and powerdebug.
• Graphics
  • dma-buf – (upstream) debugfs support released, accepted for 3.10
  • AV playback bringup on Jelly Bean on Origen Quad complete and released to android team
  • kernel – (upstream) patches to adds common FIMD device node for all Exynos4 SoCs.
  • piglit – gles2-all and android support released via git. opencl-arm established with fixes specifically for ARM
  • audio – Channel swap for panda has been fixed in 3.9 and 3.8 as well.
  • opencl – Proof of Concept SNU CPU only OpenCL lib investigated and ported to armhf, available via git
• Kernel
  • Refactor EHCI controller code
  • Depopulate the Exynos <mach-exynos/include-mach> directory
  • Expanded Binder Unit Test – Implement base ioctl unit tests
  • Depopulate the ux500 and plat-nomadik <mach/*> and <plat/*>
  • Improve eMMC Power Management Support – Merge patches to add a skeleton for doing background operations at idle time, based on runtime PM
  • Port some of the simpler platforms to multi-platform support
    • integrator: get to a state where DT is working fully as a prerequisite
    • pci: fix PCI device tree problems when resolving IRQs
    • SPEAr
    • Finalize Nomadik DT transition by moving the clocks to DT
    • Convert u300 to DT as a prerequisite
  • Android upstreaming: ashmem
  • Android alarm-dev compat_ioctl support
  • Implement and upstream ARM 32 bit uprobes (userspace probes) support
• Power Management
  • Porting guide for big.LITTLE switcher is available (https://wiki.linaro.org/Internal/Projects/Big.Little.Switcher/Docs/porting-guide).
  • cpuidle : consolidate ARM drivers
  • DVFS for the Common Clock Framework
  • thermal: Powertop Integration – Add basic RFC patch and send for review
  • Linaro PM QA 0.4.1 2013.04 released. Fixed in this release:
  • Linaro Powerdebug 0.6.3 2013-04 released. Fixed in this release:
• QA
  • Tests to cover big.LITTLE cluster init and shutdown have been added to the big.LITTLE core test suite
  • big.LITTLE extended test case scenarios have been implemented.
  • Functional and regression tests for scheduler from ARM have been integrated, covering HMP patches.
• Toolchain
  • Linaro GCC 4.8 2013.04 released, based off the latest GCC 4.8.0+svn197294 release.
    • Initial optimized support for Cortex-A53 for arm*-*-* targets.
    • Improved support for new ARMv8-A instructions for arm*-*-* and aarch64*-*-* targets.
    • Backport of optimizations concerning whether to use Neon for 64-bit bitops for arm*-*-* targets.
  • Linaro GCC 4.7 2013.04 released, based off the latest GCC 4.7.2+svn197188 release.
    • Includes arm/aarch64-4.7-branch up to svn revision 196381.
    • Backport vectorizer cost model.
    • Turn off 64-bit Bitops in Neon.
  • Linaro GCC 4.6 2013.04 released, based off the latest GCC 4.6.3+svn197511 release. It’s the last monthly release of 4.6 series.
  • Linaro Toolchain Binaries 2013.04 released, updated to Linaro GCC 4.7 2013.04 and Linaro GCC 4.8 2013.04
• LEG
  • Linaro UEFI 2013.04 released – bugfix
  • OpenSSL optimisations
  • SCT (Self-Certification Test)is now running without any crashes.
  • ACPI topic branch is being prepared for inclusion into linux-linaro tree.

Visit https://wiki.linaro.org/Cycles/1304/Release for a list of known issues and further release details about the LEB, Android, Kernel, Graphics, Landing Team,  Platform, Power management and Toolchain (GCC / Qemu) components.

Linaro 13.03 is now available, and features Linux Kernel 3.9-rc3 and Android 4.2.2.

This month, Linaro has released their first Origen Quad Android image, as well as Tiny Android build for Arndale. The ALIP image listed in the download page is still based on Ubuntu 12.11, but as doc Bormental noticed earlier this month, the latest ALIP Quantal 13.03 image is available for download at https://releases.linaro.org/latest/ubuntu/quantal-images/alip. Some development tools (gcc, g++, vi, make..) are now included in Android, so you can develop and build natively from your Android device. Linaro has kept on cleaning the Linux kernel ARM tree for Exynos and ST Ericson SoCs. More work has been done on big.LITTLE for both IKS and HMP, as well as ARMv8 OpenEmbedded, and an initial GRUB port on ARM UEFI is now available.

Here are the highlights of this release:

Karim Yaghmour, Opersys’ CEO, gave 4 training sessions dealing Embedded Android at Linaro Connect Asia 2013, in Hong Kong, earlier this month. Charbax filmed those 4 40 to 50 minutes session with excellent video and audio quality, so I encourage you to watch all sessions if you are interested in this topic. The presentation slides are available on Slideshare.

The first training session is entitled “Android Internals”, and Karim introduces Android’s overall architecture, following the agenda below:

The second session “Working with the AOSP” deals with the following key points:

• Tools and location
• Content Building
• Build tricks
• Build system architecture
• Output images
• Using adb
• Custom toolchains and dev kits
• Compatibility Test Suite
• Basic hacks

The third session entitled “Native Android user-space” gives details about Android “rootfs”:

• Filesystem layout
• Architecture vs. filesystem
• Build system and filesystem
• adb
• Command line
• Init
• ueventd
• Boot logo
• Bionic
• Tiny Android
• Legacy integration

The fourth and last session “Using and Customizing the Android Framework” is divided into 6 main parts:

• Kickstarting the Framework
• Utilities and Commands
• Native daemons
• System Services Internals
• Creating your Own System Service
• Android Framework

If you want to go further, you may want to read “Embedded Android: Porting, Extending, and Customizing” also written by Karim available in Paperpack or Kindle versions.

If you are a developer interested in getting your code into mainline, Greg KH keynote at Linaro Connect 2013 Hong Kong is probably worth a watch. In this presentation entitled “I Don’t Want Your Code! Linux Kernel Maintainers, why are they so grumpy?”, he first describes the large amount of patches they receive (7.28 patches per hour for kernel 3.8.0), gives some statistic about developers and companies involved with the kernel (about 20% is done by individuals), tells the audience they should submit the kernel code during SoC emulation/simulation stage, so that it’s accepted and ready to use when customers get the silicons (like Intel does), and quotes Intel and IBM executives saying “Working upstream saves time and money”.

He then moves on what he does not want to see (and gets a lot): patch series with missing patches, email signature saying it’s confidential (since Linux development is done publicly, he’s legally required to delete it), patch format incorrect, patch created in wrong directory or against the wrong tree, wrong coding style, patches that won’t compile, and so on. Greg explains he tries to be as nice as possible with individual developers, but he will be very strict with developers working for companies as they should know what they are doing, and 10 to 15 minutes Linaro bashing ensues… He even explains he will not accept code from one particular developer for one year unless it’s signed off by a senior Linaro developer.

He concludes by saying that if developers wants him to accept their code, they have to “give me no excuse to reject their patch”, and once that happens he will make sure the patch is reviewed within 1 or 2 weeks, and offer semi-constructive criticism, and let you know about the status of the patch.

You can also download the presentation slides. If you want to learn in details what you have to do to submit a patch, you may want to read “How to Write and Submit a Linux Kernel Patch” presentation at FOSDEM 2010.

Linaro 13.02 is now available, and features Linux Kernel 3.8 and Android 4.2.2.

The biggest news this month is probably the first release of a preliminary ARM64 Debian/Ubuntu Raring image. Other noticeable items include work on ARMv7 KVM, more improvements to OpenEmbedded ARMv8 implementation, as well as big.LITTLE MP implementation, and some modifications to the toolchain for Cortex A7 support. Origen images are not available for download this month, and there’s still no ALIP images since they have disappeared since Linaro upgraded to Ubuntu Quantal.

Here are the highlights of this release:

Visit https://wiki.linaro.org/Cycles/1302/Release for a list of known issues and further release details about the LEB, Android, Kernel, Graphics, Landing Team,  Platform, Power management and Toolchain (GCC / Qemu) components.

Samsung launched Exynos 5 Octa at CES 2013. This processor comes with 8 cores: 4 Cortex A15 cores and 4 Cortex A7 cores, and it’s the first processor that’s been announced to work in big.LITTLE configuration, where the big cores (A15) handle demanding tasks, and the LITTLE cores (A7) handle simpler tasks such as audio playback or background tasks. This is all done to optimize power consumption. There are 2 big.LITTLE software implementations: In-kernel switcher (IKS) and heterogeneous multi-processing (HMP). The first one is easier to implements but can only use 4 cores (in Exynos 5 Octa) at a time, and the second is more complex, but can handle all 8 cores, and assign individual tasks to a particular core. For more technical details about big.LITTLE implementations, you can read my previous post.

ARM and Samsung recently uploaded a video providing an overview of big.LITTLE (but instead of IKS and HMP, it’s called “Cluster Migration Mode” and “Full MP”), and showing an interesting demo (2:44) running on TC2 development platform (2x A15, 3x A7, no GPU) that shows the load all five cores, power consumption on the big cluster and LITTLE cluster, which all vary depending on the tasks. This demo runs in Linaro Android with HMP/Full MP implementation, and the software showing the load and power consumption must be ARM Development Studio 5 (DS5).