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New Freescale i.MX7 SoCs take on low-power Linux IoT

Jun 22, 2015 — by Eric Brown 11,230 views

[Updated: 7:00PM] — Freescale unveiled two Linux-ready, 28nm i.MX7 SoCs with one or two Cortex-A7 cores, Cortex-M4 MCUs, and much lower power consumption than the i.MX6.

The single-core, 800MHz i.MX7 Solo (i.MX7S) and dual-core, 1GHz i.MX7 Dual (i.MX7D) follow last month’s single-core i.MX6 UltraLite as the first i.MX system-on-chips to move to a Cortex-A7 architecture. The i.MX7 Series is also Freescale’s first new i.MX family to move backward in performance, although significantly upward in power efficiency — a testament to how the Internet of Things is changing the semiconductor business. The i.MX7 ships with Linux, and supports Android, and targets IoT, wearables, secure Point-of-Sale equipment, smart home controls, and industrial products.

The up-to-1GHz Cortex-A7 cores provided here are slower than the i.MX6’s up to 1.2GHz Cortex-A9 cores, and in ways that go beyond the clock rate comparison. In addition, there’s no mention of the earlier Vivante GPUs or 3D acceleration in general. Like the UltraLite, there’s only a simple 2D image processing engine.


On the other hand, the i.MX7 is much more power efficient than the Cortex-A9-based i.MX6, which debuted in 2011, and has been one of the leading SoCs used in embedded Linux. Freescale touts the i.MX7’s Cortex-A7 and Cortex-M4 cores for having a core efficiency levels of 100 μW/MHz and 70 μW/MHz, respectively. The SoC’s overall power efficiency is 15.7 DMIPS/mW, and a new Low Power State Retention (LPSR) mode runs at 250 μW, claims the chipmaker.

i.MX7S and i.MX7D at a glance
(click image to enlarge)

The bulk of the power savings come from switching to the newer Cortex-A7 architecture, as well as to a 28nm “ultra low leakage process,” as compared to the i.MX6’s 40nm process. The i.MX7 also features a new discrete power domain architecture. In the LPSR sleep mode, the i.MX7 is claimed to consume only 250 μW, while supporting DDR self-refresh mode, GPIO wakeup, and memory state retention.

The i.MX7 SoCs are paired with a new Freescale PF3000 PMIC, which was optimized to work with new i.MX7 power management features. The PF3000 features up to four buck converters, six linear regulators, an RTC supply, and a coin-cell charger. The chip is said to optimize power delivery to peripherals and system memory resources in addition to processor cores. The PMIC also supports one-time programmable memory for controlling startup sequence and output voltages, with no external components required.

Like the single-core i.MX6 SoloX SoC announced in February, the i.MX7 adds a Cortex-M4 microcontroller unit (MCU) core for offloading processing. The Cortex-M4 can run an RTOS such as Freescale’s own MQX, at up to 266MHz, compared to 200MHz on the SoloX.

Heterogeneous processing and high-end crypto

The i.MX7 also seems to share some of the SoloX’s new core management and security technologies. All of the i.MX7 cores can be individually power enabled using heterogeneous processing technology “in order to meet the bursty, high-performance needs of running Linux, graphical user interfaces, wireless stacks or other high-bandwidth data transfers,” says Freescale. “When high levels of processing are not needed, the work can be transferred to the smaller, lower powered Cortex-M4, enabling the power gating of the Cortex-A7 core.”

On the security side, the i.MX7 integrates Elliptic Curve Cryptography technology, active tamper detection, secure boot, and other hardware-enabled security features. The chip’s independently controlled and secured resource domains provide partitioning in order to isolate security threats and enable a hardware firewall, says Freescale.

i.MX7D (left) and i.MX7S block diagrams
(click images to enlarge)

The i.MX7S and i.MX7D are pin-to-pin and power compatible with each other. They are each equipped with a NEON multimedia engines, as well as 512KB L2 cache and 256KB SRAM. They also support 16/32-bit DDR3, DDR3L, LPDDR3, and LPDDR2 RAM, as well as NOR, QSPI, SD, NAND, and eMMC 5.0 flash memories.

In addition to differing in the speed and number of its Cortex-A7 cores, the dual-core i.MX7D is the only one to offer a PCIe x1 expansion lane, as well as an E Ink compatible ePD controller for e-reader devices. The latter supports power-sipping color or monochrome displays of up to 2048 x 1536 pixels at 106Hz.

The i.MX7D also offers dual gigabit Ethernet controllers instead of one. Both SoCs enable their GbE controllers with AVB (audio video bridging) support.

Although there does not appear to be a full GPU, the i.MX7 SoCs provide parallel RGB and MIPI-DSI display connections, as well as parallel and MIPI-CSI camera interfaces. You get USB OTG and host I/O, as well as “inter-chip” USB,” says Freescale. Other I/O includes four SPI interfaces, four single-ended-input 12-bit ADCs, and two CAN ports. You will also find I2C, UART, and more (see block diagrams above).

The i.MX7 series is supported by a SABRE development board, which includes the PF3000 PMIC, WiFi ac, and Bluetooth 4.1. You also get an SD card pre-installed with Linux. Android OS is available as an option.

Last month, in addition to announcing the stripped-down, 528MHz Cortex-A7 UltraLite, Freescale unveiled new i.MX6 DualPlus and i.MX6 QuadPlus system-on-chips that offer optimized GPUs and memory support, but keep the same 21 x 21mm packages, and remain with the same allotment of Cortex-A9 cores. The upgraded i.MX6 Plus SoCs are designed for automotive instrument clusters and infotainment systems, among other embedded applications. The two Plus models are also said to offer improved memory utilization.

i.MX8 coming soon?

A previously tipped SoC called the i.MX8 appears to be primarily aimed at automotive applications, according to marketing materials that have appeared on the web. The i.MX8 looks like it will be announced this year, with availability in 2016 or 2017.

Freescale roadmap slides showing i.MX7 and i.MX8
(click images to enlarge)

The 28-nm fabricated SoC will use 64-bit, ARMv8 Cortex-A53 cores and will be designed for advanced driver information systems and other multimedia intensive applications. Like i.MX7, the i.MX8 will also include a Cortex-M4 core.

Further information

Samples of the single-core, 800MHz i.MX7 Solo (i.MX7S) and dual-core, 1GHz i.MX7 Dual (i.MX7D) are available now, with full production planned for November. The PF3000 PMIC is available now, along with a KITPF3000FRDMEVM evaluation board and KITPF3000FRDMPGM programming board. More information on the i.MX7 Series may be found on the i.MX7 product page, and more on the PMIC may be found on Freescale’s PF3000 PMIC product page .

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