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ST announces Cortex-A7/M4 hybrid SoC and OpenSTLinux distro

Feb 21, 2019 — by Eric Brown 4,192 views

[Updated: Feb. 23] — ST unveiled a Linux-driven “STM32MP1” SoC with dual Cortex-A7 cores and a Cortex-M4 core. The SoC will be available in April with several Raspberry Pi compatible dev boards.

STMicroelectronics announced a STM32MP1 SoC that intends to ease the transition for developers moving from its STM32 microprocessor unit (MCU) family to more complex embedded systems. Development boards based on the SoC — and equipped with connectors for Raspberry Pi and Arduino add-ons — will be available in April (see farther below).

(click image to enlarge)

A reader (asdf) has corrected our earlier claim that the STM32MP1 was ST’s first Cortex-A based product and the first to run Linux. The company launched an ARM9 based SPEAr series of processors back in 2005 that eventually evolved into the dual-Cortex-A9 SPEAr1300. This is now listed under legacy processors on the ST website, and the company lists only the STM32MP1 under microprocessors on its recently updated processor overview chart.

Aimed at industrial, consumer, smart home, health, and wellness applications, the STM32MP1 features dual, 650MHz Cortex-A7 cores running a new “mainlined, open-sourced” OpenSTLinux distro with Yocto Project and OpenEmbedded underpinnings. There’s also a 209MHz Cortex-M4 chip with an FPU, MPU, and DSP instructions. The Cortex-M4 is supported by an enhanced version of ST’s STM32Cube development tools that support the Cortex-A7 cores in addition to the M4 (see below).


Like most of NXP’s recent embedded SoCs, including the single- or -dual Cortex-A7 i.MX7 and its newer, Cortex-A53 i.MX8M and i.MX8M Mini, the STM32MP1 is a hybrid Cortex-A/M design intended in ST’s words to “perform fast processing and real-time tasks on a single chip.” Hybrid Cortex-A7/M4 SoCs are also available from Renesas, Marvell, and MediaTek, which has developed a custom-built MT3620 SoC as the hardware foundation for Microsoft’s Azure Sphere IoT framework.

As a market leader in Cortex-M MCUs, ST has made a larger leap from its comfort zone than these other semiconductor vendors. NXP and Renesas are also leading MCU vendors, but they have more recent experience with Cortex-A SoCs. NXP was crafting Linux-powered SoCs long before it changed it named from Freescale.

The SM32MP1 launch continues a trend of MCU technology companies reaching out to the Linux community. One example is Arm’s new Mbed Linux distro and Pelion IoT Platform, which orchestrates s-M and Cortex-A devices under a single IoT platform.

Inside the STM32MP1

The STM32MP1 is equipped with 32KB instruction and data caches, as well as a 256KB L2 cache. ST also supplies an optional Vivante 3D GPU with support for OpenGL ES 2.0 and 24-bit parallel RGB displays at up to WXGA (1280×800) at 60fps.

The SoC supports a 2-lane MIPI-DSI interface running at 1Gbps and offers native support for Linux and application frameworks such as Android Qt and Crank Software’s Storyboard GUI. While the GPU is pretty run-of-the-mill for Cortex-A7 SoCs it’s a giant leap from the perspective of MCU developers trying to bring up modern HMI displays.

Three SoC models are available: one with 3D GPU, MIPI-DSI, and 2x CAN FD interfaces, as well as one with 2x CAN FD only and one without the GPU and CAN I/O.

STM32MP model comparison (left) and OpenSTLinux Distrib architecture
(click images to enlarge)

The STM32MP1 is touted for its rolling 10-year longevity support and heterogeneous architecture, which lets developers halt the Cortex-A7 and run only on the Cortex-M4 to reduce power consumption by 25 percent. From this mode, “going to Standby further cuts power by 2.5k times — while still supporting the resumption of Linux execution in 1 to 3 seconds, depending on the application,” says ST. The SoC includes a PMIC and other power circuitry such as buck and boost converters.

For security, the SoC provides Arm TrustZone, cryptography, hash, secure boot, anti-tamper pins, and a real-time clock. RAM support includes 32/16-bit, 533MHz DDR3, DDR3L, LPDDR2, LPDDR3. Flash support includes SD, eMMC, NAND, and NOR.

Peripherals include Cortex-A7 linked GbE, 3x USB 2.0, I2C, and multiple UART and SPI links. Analog I/O connected to the Cortex-M4 include 2x 16-bit ADCs, 2x 12-bit DACs, 29x timers, 3x watchdogs, LDOs, and up to 176 GPIOs.

OpenSTLinux and STM32Cube

The new OpenSTLinux distribution “has already been reviewed and accepted by the “Linux community: Linux Foundation, Yocto project, and Linaro,” says ST. The Linux BSP includes mainline kernel, drivers, boot chain, and Linaro’s OP-TEE (Trusted Execution Environment) security stack. It also includes Wayland/Weston, Gstreamer, and ALSA libraries.

Three Linux software development packages are available with the STM32MP1: a quick Starter package with STM32CubeMP1 samples; a Dev package with a Yocto Project SDK that lets you add your own Linux code; and an OpenEmbedded based Distrib package that also lets you create your own OpenSTLinux-based Linux distro. ST has collaborated with Timesys on the Linux BSPs and with Witekio to port Android to the STM32MP1.

STM32 developers can “easily find their marks” by using the familiar STM32Cube toolset to control both the Cortex-M4 and Cortex-A7 chips. The toolset includes GCC-based STM32CubeProgrammer and STM32CubeMX IDEs, which “include the DRAM interface tuning tool for easy configuration of the DRAM sub-system,” says ST.

Development boards

ST is supporting its STM32MP1 SoC with four development boards due in April: the entry level STM32MP157A-DK1 and STM32MP157C-DK2 and the higher end STM32MP157A-EV1 and STM32MP157C-EV1. All the boards offer GPIO connectors for the Raspberry Pi and Arduino Uno V3.

STM32MP157C-DK2 (left) and STM32MP157C-EV1
(click images to enlarge)

The DK1/DK2 boards are equipped with 4GB DDR3L, as well as USB Type-C, USB Type-A OTG, HDMI, and MIPI-DSI. You also get GbE and WiFi/Bluetooth, and a 4-inch, VGA capacitive touch panel, among other features.

The more advanced A-EV1 and C-EV1 boards support up to 8GB DDR3L, 32GB eMMCv5.0. a microSD slot, and SPI and NAND flash. They provide most of the features of the DK boards, as well as CAN, camera support, SAI, SPDIF, digital mics, analog audio, and much more. They also supply 4x USB host ports and a micro-USB port. A 5.5-inch 720×1280 touchscreen is available.

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