Dev Board datasheet

Overview

The Coral Dev Board is a single-board computer with a removable system-on-module (SOM) that contains eMMC, SOC, wireless radios, and the Edge TPU. You can use the Dev Board as a single-board computer when you need accelerated ML processing in a small form factor, but it also serves as an evaluation kit for the SOM. You can use the dev board to prototype internet-of-things (IOT) devices and other embedded systems that demand fast on-device ML inferencing, and then scale to production using just the 40 mm × 48 mm SOM board combined with your custom PCB hardware using board-to-board connectors.

The SOM is based on NXP's iMX8M system-on-chip (SOC), but its unique power comes from the Edge TPU coprocessor. The Edge TPU is a small ASIC designed by Google that provides high performance ML inferencing with a low power cost. For example, it can execute state-of-the-art mobile vision models such as MobileNet v2 at 100+ fps, in a power efficient manner.

Edge TPU key benefits:

  • High speed TensorFlow Lite inferencing
  • Low power
  • Small footprint

The baseboard includes all the peripheral connections you need to prototype a project, including USB 2.0/3.0 ports, DSI display interface, CSI-2 camera interface, Ethernet port, speaker terminals, and a 40-pin GPIO header.

Hardware overview

The Coral Dev Board is composed of the Edge TPU Module (SOM) and a development baseboard. The SOM connects to the baseboard with three 100-pin connectors.

The SOM is based on NXP's iMX8M system-on-chip (SOC) provides an application processor to host your embedded operating system, Wi-Fi and Bluetooth connectivity, cryptographic security, and accelerated ML inferencing. The baseboard primarily serves as a prototyping board that allows you to connect other hardware peripherals to the system.

Figures 1 and 2 illustrate the core components on the baseboard and SOM.

Figure 1. Block diagram of the baseboard components
Figure 2. Block diagram of the SOM components

Components overview

Dev board dimensions

Figure 3. Coral Dev Board dimensions

Baseboard connections

The baseboard on the Coral Dev Board provides a variety of connectors as shown in figure 4.

Figure 4. Connectors on the Coral Dev Board

GPIO header pinout

All GPIO pins are powered by the 3.3V power rail, with a programmable impedance of 40 - 255 ohms, and a max current of ~ 82 mA. You can interact with each pin using standard Linux interfaces such as device files (/dev) and sysfs files (/sys).

All GPIO pins have a 90k pull-down resistor inside the iMX8M SOC that is used by default during bootup, except for the I2C pins, which instead have a pull-up to 3.3V on the SOM. However, these can all be changed with a device tree overlay that loads after bootup.

Caution: Do not connect a device that draws more than ~ 82 mA of power or you will brownout the system.
Figure 5. Pinout for the 40-pin GPIO header

Universal Asynchronous Receiver-Transmitter (UART)

Each UARTv2 module supports the following:

  • 7- or 8-bit data words, 1 or 2 stop bits, programmable parity (even, odd, or none).
  • Programmable baud rates up to 4 Mbps.
  • 32-byte FIFO on Tx and 32 half-word FIFO on Rx supporting auto-baud.

Synchronous Audio Interface (SAI)

Each SAI module supports full duplex serial interfaces with frame synchronization, such as I2S, AC97, TDM, and codec/DSP interfaces.

Inter-Integrated Circuit (I2C)

Serial interface for external devices.

Serial Peripheral Interface (SPI)

Full-duplex enhanced Synchronous Serial Interface, with data rate up to 52 Mbit/s. Configurable to support Master/Slave modes, four chip selects to support multiple peripherals.

Pulse Width Modulation (PMW)

Operates on a frequency of 0 - 66Mhz. Provides a 16-bit counter and is optimized to generate sound from stored sample audio images. It can drive motors and generate tones. It uses 16-bit resolution and a 4x16 data FIFO to generate sound.

Serial console port

The micro-USB port (see "serial console" in figure 4) provides access to the serial console based on the CP210x USB to UART Bridge Controller. Only Linux is officially supported for serial console connections, but you might have success from another platform if you install the appropriate CP210x USB to UART Bridge Virtual COM Port (VCP) driver.

To connect, first determine the device filename for the serial connection by running this command on your Linux computer:

dmesg | grep ttyUSB

You should see two results such as this:

[ 6437.706335] usb 2-13.1: cp210x converter now attached to ttyUSB0
[ 6437.708049] usb 2-13.1: cp210x converter now attached to ttyUSB1

Then use the name of the first filename listed as a cp210x converter to open the serial console connection (this example uses ttyUSB0 as shown from above):

screen /dev/ttyUSB0 115200

You should now be connected.

HDMI port

This is a full-size HDMI 2.0a port.

By default, the output is locked at a resolution of 1920 x 1080 to avoid GPU pressure and power costs when driving higher resolution displays.

If your display does not support 1920 x 1080, you can change this setting by editing file at /etc/xdg/weston/weston.ini: In the [output] section, edit the line mode=1920x1080 to be a resolution of your choice. You may also delete this line completely, and it will then use the highest resolution supported by the monitor (but doing so can degrade the overall system performance if it is higher than 1920x1080).

USB 3.0 ports

There are three USB 3.0 ports:

  • USB Type-A host: Operates as a USB 3.0 host that can provide power. Use this port for your peripherals, such as a USB camera.

    Caution: Do not connect a device that draws more than 1 amp of power or you will brownout the system.

  • USB Type-C data: Operates as a USB "on the go" (OTG) device port, so the Dev Board appears as a USB device to a connected host device. Use this port to connect via SSH over USB or to flash the board.

  • USB Type-C power: Use this to power the board with a 2 - 3A at 5V DC connection.

Ethernet port

The Gigabit Ethernet port (RJ45) supports 10/100/1000 Mbps Ethernet/IEEE 802.3 networks.

4-pin stereo terminal

We recommend using a 4 Ohm, 3 watt speaker. A higher Ohmage results in a much quieter output.

The stereo terminal is a 4-pin 2.54mm-pitch terminal connector for stereo speakers. Wire functions are as follows (from left to right, as shown in figure 6):

  • 1: Speaker left positive
  • 2: Speaker left negative
  • 3: Speaker right positive
  • 4: Speaker right negative
Figure 6. Stereo speaker terminals

MicroSD slot

The MicroSD card meets the SD/SDIO standard, up to version 3.0. It can be used as expanded memory for the system or as the disk for the system image. If the entire system fails, you can use the SD card to reflash u-boot onto the board (see the flashing instructions).

MIPI DSI display connector

The MIPI DSI display connector is a 39-pin flex cable connector that provides 4 lanes with resolution up to 1920x1080 at 60Hz. The connector pinout is as follows.

Pin #NamePin #Name
1GND21DSI_TE
2---TP522---
3---TP2023V1V8
4---TP224---
5GND25DISP_LEDA
6MIPI_DSI_D2_P26DISP_LEDK1
7MIPI_DSI_D2_N27DISP_LEDK2
8GND28VOP_5p5_CONN
9MIPI_DSI_D1_P29VON_N5p5_CONN
10MIPI_DSI_D1_N30LED_PWM
11GND31GND
12MIPI_DSI_CLK_P32GND
13MIPI_DSI_CLK_N33--- TP21
14GND34GND
15MIPI_DSI_D0_P35DISPLAY_I2C_SCL_1V8
16MIPI_DSI_D0_N36DISPLAY_I2C_SDA_1V8
17GND37DSI_VSP_EN
18MIPI_DSI_D3_P38DSI_TS_nINT
19MIPI_DSI_D3_N39DSI_RESETB
20GND

MIPI CSI-2 camera connector pinout

The MIPI CSI-2 camera connector is a 24-pin flex cable connector that's designed for the Coral Camera Module. The connector pinout is as follows.

Pin #NamePin #Name
1GND13GND
2MIPI_CSI_D0N14MIPI_CSI_D3N
3MIPI_CSI_D0P15MIPI_CSI_D3P
4GND16GND
5MIPI_CSI_D1N17CAM_PWDNB
6MIPI_CSI_D1P18CAM_CLK
7GND19GND
8MIPI_CSI_CLKN20CAM_I2C_SCL
9MIPI_CSI_CLKP21CAM_I2C_SDA
10GND22VSYNC
11MIPI_CSI_D2N23CAM_RESETB
12MIPI_CSI_D2P243V3
Figure 7. Camera adapter card diagram

Power specifications

The Coral Dev Board must be powered by 2 - 3A at 5V DC using the USB Type-C power port (see figure 4).

Caution: Do not attempt to power the board by connecting it to your computer.

The SOM has one primary PMIC (BD71837MWV) from Rohm for the iMX8M SOC complex, LPDDR4, eMMC, and Wi-Fi/Bluetooth. It integrates 8 DC-DC buck regulators and 7 LDOs to provide all power rails required by iMX8M SOC and commonly used peripherals.

Boot mode

The baseboard includes 4 switches (indicated in figure 8) to control the boot mode. By default, they are set to boot from eMMC. You can change the boot mode as follows.

Boot modeSwitch 1Switch 2Switch 3Switch 4
Serial downloadOffOn[Don't care][Don't care]
eMMCOnOffOffOff
SD cardOnOffOnOn
Figure 8. Boot mode switches, set to boot from eMMC

System reset

You can restart the system with the RESET button shown in figure 9.

Figure 9. System reset button

Software and operation

The Dev Board factory setting includes only the u-boot bootloader software on the eMMC memory. To use the board, you need to flash the Mendel operating system (a derivative of Debian Linux). For instructions, see the Get started guide.

The Mendel system includes software that's specially-designed for the Dev Board and required to operate the Edge TPU. It also includes Python APIs that make it easy to perform inferences with TensorFlow Lite models.

For information about how to create models and run inferences on the Edge TPU, read TensorFlow models on the Edge TPU.

Caution: Avoid touching the heat sink during operation. Whether or not the fan is running, the heat sink can become very hot to the touch and might cause burn injuries.
Note: This datasheet does not provide complete details on the SOM. The following information is primarily a look at the board-to-board connectors for those interested in using the SOM with custom PCB hardware. A more detailed SOM datasheet is available upon request.

The SOM is based on NXP's iMX8M system-on-chip (SOC) and contains all the essential hardware systems, including the Edge TPU and Wi-Fi/Bluetooth radios. It is attached to the Dev Board baseboard with three 100-pin board-to-board connectors.

Figure 10. Edge TPU SOM dimensions without the fan

Board to board connectors

The Edge TPU SOM connects to the host baseboard with three 100-pin connectors, as shown in figure 11.

These are Hirose Electric 100-position connector plugs (DF40C-100DP-0.4V(51)). They connect to the corresponding 100-position connector receptacles (DF40HC(3.0)-100DS-0.4V(51)) on the baseboard.

Figure 11. Module bottom with connector locations (in millimeters), the position for pin 1 on each connector is indicated with a yellow square
Figure 12. SOM board-to-board connector pinout

Pinout by function

To ensure reliable operation and performance, the board should operate in the following environment:

  • Temperature: 0 - 50°C

Thermal solution

To maintain functional heat levels the Dev Board includes a heat sink and a fan with the following specifications:

  • Speed: 9k RPM
  • Airflow: 138 LPM (4.9 CFM)
  • Voltage: 5 V DC
  • Power (peak): 0.65 W
  • Static pressure: 42 Pa (0.17 in-H2O)
Caution: Avoid touching the heat sink during operation. Whether or not the fan is running, the heat sink can become very hot to the touch and might cause burn injuries.

Environmental and mechanical reliability tests

TestConditionsVerified
Temp cyclingNon-op, -40°C (LT) to 85°C (HT), 7 minute ramp, 23 minutes dwell, 60 minutes/cycle200 cycles
Heat soakNon-op, 85°C/85% RH200 cycles
Audio jack cycling50% manual plug/unplug, 50% uniaxial machine plug/ unplug1000 cycles
HDMI cyclingManual plug/unplug100 cycles
MicroSD cyclingManual plug/unplug100 cycles
Vibration3 axes (X, Y and Z), 15 minutes per axis, 10-500Hz. Amplitude: 2.16 Grms45 minutes
USB-C connector cyclingManual plug/unplug1000 cycles
USB-A connector cyclingManual plug/unplug1000 cycles
Micro USB connector cyclingManual plug/unplug1000 cycles
Fan run life40°C, 65% RH70k hours

Certifications

MarketCertifications
USAFCC
European UnionCE