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Google launches i.MX8M dev board with Edge TPU AI chip

Mar 5, 2019 — by Eric Brown — 4652 views

Google has launched a sandwich-style, $150 “Coral Dev Board” with an RPi-like 40-pin header that runs Linux on an i.MX8M with an Edge TPU chip for accelerating TensorFlow Lite. The USB stick version sells for $75.

Google unveiled its embedded oriented Edge TPU version of its Tensor Processing Unit AI chip in July. More details quickly followed on its Linux-driven Edge TPU dev kit and USB stick version of the Edge TPU chip called the Edge TPU Accelerator. Now Mouser has opened pre-orders for both devices selling for $150 and $75, respectively, with shipments expected soon.

Google also announced a $25 MIPI-CSI 5-megapixal camera for the dev board. There are also plans to release a compute module version of the dev board and a PCIe card version of the USB stick later this year.



Coral Dev Board
(click images to enlarge)

The Edge TPU dev kit, which appears to be Google’s first Linux hacker board, is now called the Coral Dev Board. The Edge TPU dev kit is now called the Coral USB Accelerator.

The NXP i.MX8m based Coral Dev Board appears to be an open-spec design that should fit the requirements for our Linux hacker board catalogs. It would join other open-spec i.MX8M SBCs such as the HummingBoard Pulse. Like SolidRun’s Pulse, the Coral is a sandwich-style board with a removable compute module. The big difference from the expanding field of i.MX8M boards is that the Coral SOM module integrates Google’s Edge TPU neural network co-processor.

The Edge TPU is a stripped-down version of Google’s TPU Unit designed to run TensorFlow Lite ML models on Arm Linux based IoT gateways running on boards like the Coral. The gateways connect to Google Cloud services that are optimized with full-strength Cloud TPU chips to work together via Google’s new Cloud IoT Edge framework. Edge TPU enables concurrent execution of multiple AI models per frame on a high-resolution video at 30fps.

The Cloud Edge IoT stack is designed to facilitate cloud-integrated IoT edge computing and analytics. Developers can build and train ML models in the cloud and run the models on the Cloud IoT Edge device using the Edge TPU chip, thereby enabling “local, real-time, intelligent decisions,” says Google. According to the Hackster.io report that alerted us to the Coral, more details should emerge later this week with the formal announcement of the Coral at the TensorFlow Dev Summit in Sunnyvale, Calif., Mar. 6-7. Yet, Google has already exhaustively documented the Coral Dev Board, SOM, and USB Accelerator.

 
Coral USB and PCIe Accelerators

The 65 x 30 mm Coral USB Accelerator connects to Linux-based systems via a USB Type-C port to accelerate ML inferencing via its integrated Edge TPU chip. The Type-C port also draws 500mA power from the system.



Coral USB Accelerator
(click image to enlarge)

The USB Accelerator can even work with a Raspberry Pi board, although only at USB 2.0 speeds. The stick computer is built around a 32-bit, 32MHz Cortex-M0+ chip with 16KB of flash and 2KB of RAM.


PCI-E Accelerator
(click image to enlarge)

The PCI-E Accelerator card will be available later this year. Like the USB Accelerator, it can accelerate TensorFlow Lite inferences on Linux systems via the built-in Edge TPU chip. Google lists a 30 x 22mm footprint, but the illustration suggests there are two different configurations with different PCIe connectors.

 
Coral SOM

The Coral System-on-Module, which joins numerous i.MX8M based compute modules, most recently including Embedian’s SMARC-iMX8M, measures 48 x 40 x 5mm. (The teaser page erroneously calls its 40 x 40mm.) The removable module runs Debian Linux on the quad-core version of the up to 1.5GHz Cortex-A53 SoC, which also includes a Vivante GC7000Lite GPU and VPU and a 266MHz Cortex-M4 MCU.



Coral SOM, front and back
(click image to enlarge)

The Coral SOM adds the Edge TPU chip, which communicates with the i.MX8M via PCIe and I2C/GPIO. There’s also a crypto coprocessor, 1GB LPDDR4, and 8GB eMMC.

The 1GB RAM limitation is really the only head-scratcher among all the Coral SOM and SBC specs. Almost every other i.MX8M board we’ve seen starts at 2GB to 4GB, and few even offer a 1GB option. Perhaps the idea is that you’re primarily prototyping the Edge TPU chip with cloud support so you do not need to stress the i.MX8M itself.



Coral SOM block diagram and Edge TPU chip
(click images to enlarge)

The Coral SOM’s wireless module supplies dual-band 802.11b/g/n/ac and Bluetooth 4.1 with BLE. PMICs are available both for the i.MX8M and the Edge TPU chip.

 
Coral Dev Board

The Coral carrier board is listed as a Raspberry Pi-like 85 x 56mm in the photo and on the Mouser page, but it’s shown as 88.1 x 59.9 x 22.38 including the topside fan thermal unit in the datasheet. In any case, the board has a somewhat Raspberry Pi like layout and offers a “Raspberry Pi like” 40-pin GPIO connector. The Coral SOM connects to the baseboard with 3x 100-pin connectors.



Coral Dev Board, front and back
(click image to enlarge)

The Coral board is equipped with a microSD slot, as well as GbE, USB 3.0 host, USB Type-C OTG, USB Type-C 5V power, and micro-USB 2.0 serial console ports. Media I/O includes a full-size, 4Kp60-ready HDMI 2.0a port and 4-lane MIPI-DSI and CSI interfaces via FFC connectors.


Coral Dev Board detail view
(click image to enlarge)

There’s also a 3.5mm audio jack, 2x digital PDM mics, and a 4-pin terminal for stereo speakers (see image further below). The board runs at 0 to 50°C.


Coral Dev Board block diagram and pinout
(click images to enlarge)

The optional, $25, MIPI-CSI Coral Camera is a ribbon cable connected 5-megapixel model with a Omnivision OV5645 sensor. The 25 x 25mm camera’s block diagram is posted in the Coral datasheet.


Optional Coral Camera (left) and closeup of Coral Dev Board speaker interface
(click images to enlarge)

Specifications listed for the Coral Dev Board include:

  • Processor (via Coral SOM) — NXP i.MX8M (4x Cortex-A53 @ 1.5GHz); Vivante GC7000Lite/GC7000VLX for OpenGL/ES 3.1, OpenGL 3.0, Vulkan, OpenCL 1.2 GPU; Cortex-M4 @ 266MHz; separate Edge TPU Accelerator and crypto coprocessor
  • Memory/storage:
    • 1GB LPDDR4 RAM (via Coral SOM)
    • 8GB eMMC flash (via Coral SOM)
    • MicroSD slot
  • Wireless (via Coral SOM) — 802.11 b/g/n/ac 2×2 MIMO and Bluetooth 4.1 BLE
  • Networking — GbE port
  • Media I/O:
    • HDMI 2.0a output port (4K)
    • MIPI-DSI (4-lane)
    • MIPI-CSI (4-lane)
    • Optional 5-megapixel CSI camera
    • 3.5mm audio jack
    • 2x digital PDM microphones
    • 4-pin terminal for stereo speakers
  • Other I/O:
    • USB 3.0 host port
    • USB 3.0 Type C OTG port
    • USB 3.0 Type C 5V power port
    • Micro-USB serial console port
  • Expansion — 40-pin GPIO connector
  • Power — 5V DC via USB Type-C; 2x PMICs via Coral SOM
  • Operating temperature — 0 to 50°C
  • Dimensions — 88.1 x 59.9 x 22.38 including fan (possibly 85 x 56mm)
  • Operating system — Debian Linux

 
Further information

The Coral Dev Board with Coral SOM is available for $150 at Google and Mouser, but currently only via phone orders. The Hacker.io story suggests it should start shipping to early buyers within the week. The same schedule likely pertains to the $75 USB Accelerator. The Coral SOM and PCI-E Accelerator will be available later this year, with pricing undisclosed. More information on all these products may be found on Google’s Coral Beta website.

 

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