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TI's Sitara SDK moves to mainline Linux

Mar 31, 2014 — by Eric Brown 5,871 views

TI released Sitara Linux SDK 7.0, now based on the mainline Linux kernel. The SDK supports the Sitara AM335x, and coming soon, the new Sitara AM4x and AM5x.

The Sitara Linux Software Development Kit 7.0 incorporates the Texas Instruments Arago Linux distribution and a stable mainline Linux kernel. The SDK also includes the U-Boot bootloader, a Yocto Project OpenEmbedded Core file system, and Linaro toolchain.

Texas Instruments is initially making the SDK available for the Sitara AM335x, which encompasses a half dozen ARM Cortex-A8 system-on-chips ranging from 800MHz to 1GHz. Higher-end models, including the AM3359 SoC found on the BeagleBone Black, feature a 3D graphics accelerator and TI’s programmable PRU-ICSS subsystem for customizing industrial I/O.

TI Sitara AM335x versions compared
(click image to enlarge)

According to TI, all future Linux-supported ARM processors will go mainline, including the upcoming Cortex-A9 based Sitara AM4x and Cortex-A15-based Sitara AM5x (see farther below). The server-oriented, Cortex-A15 based KeyStone will also gain mainline support.

Sitara Linux SDK architecture
(click image to enlarge)

Linking the SDK to’s latest mainline kernel makes it easier for developers to “continuously access the latest devices, features, and bug fixes, says TI. Mainline Linux refers to those extra robust kernel releases during the year that have been designated by as “stable.” The current stable Linux kernel, v3.12, was released last November.


The mainline approach is said to enable a regular cadence of incremental updates, thereby easing kernel migration by letting developers build upon previous versions. Using mainline Linux streamlines the conversion of product code bases between kernel environments, as well as across a manufacturer’s product lines, says TI.

Mainline kernel development process
(click image to enlarge)

TI says it is collaborating with the community on code reviews “with stringent acceptance criteria.” TI was listed as one of the top five Linux kernel contributors in a 2013 Linux Foundation Kernel Report.

The company says it will continue to maintain stress tests for the Linux kernel across various customer use cases and applications. In addition, TI provides “easy-to-read change logs and release notes,” to help customers decide when to migrate, says the company.

Commitment to LTS

In a related move, TI also said it is committed to offering annual support for long-term stable (LTS) kernels in its Linux SDKs, starting in the fourth quarter with an update to the Sitara SDK. The LTS support will offer a long-term, community-based kernel that extends across the embedded lifecycle, and supports upstream activities for embedded engineers, says TI.

There’s been increasing focus on LTS support in the Linux kernel community, under the direction of lead kernel maintainer Greg Kroah-Hartman. In 2011, the Linux Foundation launched a Long Term Support Initiative (LTSI) working group for the two to three year lifespan of consumer electronics.

It does not appear that other existing Cortex-A8 Sitara lines will get the updated, mainline-based SDK. These include the 600MHz Sitara AM35x, the 800MHz Sitara AM37x, and the 800MHz Sitara AM38x. Also missing from the list are the half dozen ARM9-based Sitara AM1x processors, such as the AM1808 found in the Lego Mindstorms EV3 robot kit.

Coming soon: Sitara AM4x and AM5x

TI announced the Sitara AMx4 and AMx5 SoCs back in November at the SPS IPC Drives show in Germany. Designed as upgrades to the Sitara AM335x, the Linux- and Android-ready SoCs move up to dual-core Cortex-A9 and Cortex-A15 designs, respectively.

Sitara AM4x and AM5x features
(click image to enlarge)

The Sitara AM4x and AM5x provide a redesigned PRU-ICSS (Programmable Real-Time Unit and Industrial Communication Subsystem), adding a second PRU. This enables custom I/O development for simultaneous industrial Ethernet protocols and motor feedback protocols.

The 1GHz AM4x, due to ship in the first half of 2014, is optimized for industrial drive applications. It provides integrated industrial Ethernet communications, motor control peripherals, a sigma-delta modulator for current sensing, as well as position feedback protocols. Various fieldbus communication options are also available.

On the AM4x, supported Ethernet protocols include EtherCAT, PROFINET, EtherNet/IP, PROFIBUS, PowerLink, and Sercos 3. The protocols are designed to help connect drives to PLC (programmable logic controller) and HMI (human machine interface) systems. The second PRU adds support for newer motor control feedback protocols such as the EnDAT 2.2 protocol for precise feedback and position control.

Sitara AM4x block diagram
(click image to enlarge)

Like TI’s OMAP5432, the Sitara AM5x offers dual, 1.5GHz Cortex-A15 cores. Due to ship in 2H 2014, it also supplies a redesigned, dual PRU-ICSS subsystem, but it’s unclear whether it will support precisely the same features as the AM4x. Instead of focusing on drive controls, its main target is multimedia HMIs with touchscreen control.

Like the AM4x, the AM5x supports QSPI, GPIO, and PWM interfaces, as well as dual gigabit Ethernet ports. Unlike the AM4x, it also offers multimedia accelerators, DDR3 ECC support, and PCI Express expansion.

According to a Mar. 12 Control Design report, the AM4x and AM5x are part of a larger trend in industrial automation to replace PLCs with similar controls integrated on the control processor. The story also notes that TI is collaborating with 3S-Smart Software to integrate its Linux-based CoDeSys 3.5 PLC software with the AM5x.

Further information

TI’s Sitara Linux SDK 7.0, supporting the latest mainline Linux kernel, is now available for download for the AM335x family of processors. Support for the AM4x and AM5x will be added later this year. More information should be available here. More information on the Sitara AM4x may be found in TI’s AM4x data sheet (PDF).

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