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CB2

Product Profile

The BIGTREETECH CB2, compatible with the Raspberry Pi CM4 form factor, uses two 100-pin high-speed board-to-board (BTB) connectors for easy and quick connection with external expansion baseboards. It offers an alternative with similar IO capabilities, including Micro HDMI, USB, Gigabit Ethernet, DSI, and CSI outputs. Additionally, it features 2.4G and 5G WiFi, Bluetooth 5.2, the Rockchip RK3566 SoC, 2GB LPDDR4 RAM, and 32GB eMMC storage.

Product Link: BIGTREETECH Official Website

Features Highlights

  • CPU: Rockchip RK3566, quad-core Cortex-A55 @1.8GHz
  • GPU: Mali-G52 1-Core-2EE
  • NPU: 0.8 TOPS NPU
  • RAM: 2GB/4GB LPDDR4
  • Onboard EMMC
  • MIPI DSI display support
  • Dual-lane MIPI CSI-2 Camera Interface
  • 3x USB 2.0 ports, 1x USB 3.0 port
  • PCIe 2.1 1x1 Lane
  • Gigabit Ethernet +433Mbps WiFi+BT5.0
  • 40-pin GPIO
  • BTB socket that is completely identical to the one on the Raspberry Pi CM4

Specifications

Dimensions 40mm x 55mm
Mounting Dimensions 33mm x 48mm
Input Voltage 5V±5%/2A
Output Voltage 3.3V±2%/100mA
Output Voltage 1.8V±2%/100mA
WiFi 2.4G/5G, 802.11 ac/a/b/g/n/ wireless standards

Dimensions

Peripheral Interface

Pin Description

PIN Connector Signal Description
1 A connector_01 GND
2 A connector_02 GND
3 A connector_03 GBIT_MDI3_P
4 A connector_04 GBIT_MDI1_P
5 A connector_05 GBIT_MDI3_N
6 A connector_06 GBIT_MDI1_N
7 A connector_07 GND
8 A connector_08 GND
9 A connector_09 GBIT_MDI2_N
10 A connector_10 GBIT_MDI0_N
11 A connector_11 GBIT_MDI2_P
12 A connector_12 GBIT_MDI0_P
13 A connector_13 GND
14 A connector_14 GND
15 A connector_15 1000M_LED
16 A connector_16 CAMERAB_PDN_L
17 A connector_17 100M_LED
18 A connector_18 SPDIF_TX_M2
19 A connector_19 PWM3_IR
20 A connector_20 NC
21 A connector_21 WORKING_LEDEN_H
22 A connector_22 GND
23 A connector_23 GND
24 A connector_24 GPIO0_C3
25 A connector_25 GPIO4_C2
26 A connector_26 GPIO4_C5
27 A connector_27 GPIO4_C3
28 A connector_28 GPIO0_C0
29 A connector_29 GPIO0_A0
30 A connector_30 GPIO3_D7
31 A connector_31 GPIO0_C1
32 A connector_32 GND
33 A connector_33 GND
34 A connector_34 NC
35 A connector_35 GPIO0_B3
36 A connector_36 GPIO0_B4
37 A connector_37 GPIO0_A6
38 A connector_38 GPIO3_C3
39 A connector_39 GPIO4_A2
40 A connector_40 GPIO3_C2
41 A connector_41 GPIO3_C4
42 A connector_42 GND
43 A connector_43 GND
44 A connector_44 GPIO3_C1
45 A connector_45 GPIO4_A3
46 A connector_46 GPIO1_A1
47 A connector_47 GPIO4_C6
48 A connector_48 GPIO1_A0
49 A connector_49 GPIO0_C0
50 A connector_50 GPIO0_C7
51 A connector_51 GPIO0_D0 DEBUG UART
52 A connector_52 GND
53 A connector_53 GND
54 A connector_54 GPIO3_A1
55 A connector_55 GPIO0_D1 DEBUG UART
56 A connector_56 GPIO4_B3
57 A connector_57 SDC0-CLK SDCARD Clock signal
58 A connector_58 GPIO4_B2
59 A connector_59 GND
60 A connector_60 GND
61 A connector_61 SDC0-D3 SDCARD Data3 signal
62 A connector_62 SDC0-CMD SDCARD CMD signal
63 A connector_63 SDC0-D0 SDCARD Data0 signal
64 A connector_64 NC
65 A connector_65 GND
66 A connector_66 GND
67 A connector_67 SDC0-D1 SDCARD Data1 signal
68 A connector_68 NC
69 A connector_69 SDC0-D2 SDCARD Data2 signal
70 A connector_70 NC
71 A connector_71 GND
72 A connector_72 NC
73 A connector_73 GPIO0_B5
74 A connector_74 GND
75 A connector_75 GPIO3_D2
76 A connector_76 GPIO3_D3 SDCARD detect
77 A connector_77 VCC_5V 5V IN /2A
78 A connector_78 NC
79 A connector_79 VCC_5V 5V IN /2A
80 A connector_80 GPIO4_B5
81 A connector_81 VCC_5V 5V IN /2A
82 A connector_82 GPIO4_B4
83 A connector_83 VCC_5V 5V IN /2A
84 A connector_84 3V3 3.3v out /200mA
85 A connector_85 VCC_5V 5V IN /2A
86 A connector_86 3V3 3.3v out /200mA
87 A connector_87 VCC_5V 5V IN /2A
88 A connector_88 1V8 1.8v out /100mA
89 A connector_89 GPIO3_B4
90 A connector_90 1V8 1.8v out /100mA
91 A connector_91 NC
92 A connector_92 PWRON
93 A connector_93 RECOVERY
94 A connector_94 NC
95 A connector_95 GPIO4_A1
96 A connector_96 NC
97 A connector_97 GPIO4_A5
98 A connector_98 GND
99 A connector_99 PMIC_PWRON
100 A connector_100 AP-RESET
101 B connector_1 USB_OTG0_ID
102 B connector_2 PCIE20_CLKREQn_M 2
103 B connector_3 USB_OTG0_DM
104 B connector_4 LINEOUTL
105 B connector_5 USB_OTG0_DP
106 B connector_6 LINEOUTR
107 B connector_7 GND
108 B connector_8 GND
109 B connector_9 PCIE20_PERSTn_M2
110 B connector_10 PCIE20_REFCLKP
111 B connector_11 GPIO4_B0
112 B connector_12 PCIE20_REFCLKN
113 B connector_13 GND
114 B connector_14 GND
115 B connector_15 MIPI_CSI_RX_D0N
116 B connector_16 PCIE20_RXP
117 B connector_17 MIPI_CSI_RX_D0P
118 B connector_18 PCIE20_RXN
119 B connector_19 GND
120 B connector_20 GND
121 B connector_21 MIPI_CSI_RX_D1N
122 B connector_22 PCIE20_TXP
123 B connector_23 MIPI_CSI_RX_D1P
124 B connector_24 PCIE20_TXN
125 B connector_25 GND
126 B connector_26 GND
127 B connector_27 MIPI_CSI_RX_CLK0N
128 B connector_28 USB3-DM
129 B connector_29 MIPI_CSI_RX_CLK0P
130 B connector_30 USB3-DP
131 B connector_31 GND
132 B connector_32 GND
133 B connector_33 MIPI_CSI_RX_D2N
134 B connector_34 MIC1_IN
135 B connector_35 MIPI_CSI_RX_D2P
136 B connector_36 MIC2_IN
137 B connector_37 GND
138 B connector_38 GND
139 B connector_39 MIPI_CSI_RX_D3N
140 B connector_40 MIPI_CSI_RX_CLK1N
141 B connector_41 MIPI_CSI_RX_D3P
142 B connector_42 MIPI_CSI_RX_CLK1P
143 B connector_43 GPIO4_A7
144 B connector_44 GND
145 B connector_45 HP_SNS
146 B connector_46 USB2_HOST2_DP
147 B connector_47 HP_DET_L
148 B connector_48 USB2_HOST2_DM
149 B connector_49 SARADC_VIN2
150 B connector_50 GND
151 B connector_51 HCEC HDMI CEC
152 B connector_52 USB3_HOST1_DP
153 B connector_53 HHPD HDMI Hotplug
154 B connector_54 USB3_HOST1_DM
155 B connector_55 GND
156 B connector_56 GND
157 B connector_57 MIPI_DSI_TX0_D0N
158 B connector_58 USB3_HOST1_SSTXP
159 B connector_59 MIPI_DSI_TX0_D0P
160 B connector_60 USB3_HOST1_SSTXN
161 B connector_61 GND
162 B connector_62 GND
163 B connector_63 MIPI_DSI_TX0_D1N
164 B connector_64 USB3_HOST1_SSRXP
165 B connector_65 MIPI_DSI_TX0_D1P
166 B connector_66 USB3_HOST1_SSRXN
167 B connector_67 GND
168 B connector_68 GND
169 B connector_69 MIPI_DSI_TX0_CLKN
170 B connector_70 HTX2P HDMI TX2 Positive.
171 B connector_71 MIPI_DSI_TX0_CLKP
172 B connector_72 HTX2N HDMI TX2 Negative.
173 B connector_73 GND
174 B connector_74 GND
175 B connector_75 MIPI_DSI_TX1_D0N
176 B connector_76 HTX1P HDMI TX1 Positive.
177 B connector_77 MIPI_DSI_TX1_D0P
178 B connector_78 HTX1N HDMI TX1 Negative.
179 B connector_79 GND
180 B connector_80 GND
181 B connector_81 MIPI_DSI_TX1_D1N
182 B connector_82 HTX0P HDMI TX0 Positive.
183 B connector_83 MIPI_DSI_TX1_D1P
184 B connector_84 HTX0N HDMI TX0 Negative.
185 B connector_85 GND
186 B connector_86 GND
187 B connector_87 MIPI_DSI_TX1_CLKN
188 B connector_88 HTXCP HDMI CLK Positive.
189 B connector_89 MIPI_DSI_TX1_CLKP
190 B connector_90 HTXCN HDMI CLK Negative.
191 B connector_91 GND
192 B connector_92 GND
193 B connector_93 MIPI_DSI_TX1_D2N
194 B connector_94 MIPI_DSI_TX1_D3N
195 B connector_95 MIPI_DSI_TX1_D2P
196 B connector_96 MIPI_DSI_TX1_D3P
197 B connector_97 GND
198 B connector_97 GND
199 B connector_99 HSDA HDMI I2C
200 B connector_100 HSCL HDMI I2C

Interface Introduction

SW1 Button Explanation

Pressing and holding down SW1 will short-circuit the eMMC signal line to GND, prohibiting communication between SoC and eMMC.

40 pin GPIO

The calculation method for GPIO pins is as follows:

GPIO4_B2 = (‘B’ - ‘A’) * 8 + 2 = 1 * 8 + 2 = gpiochip4/gpio10

GPIO3_D7 = (‘D’ - ‘A’) * 8 + 7 = 3 * 8 + 7 = gpiochip3/gpio31

Flashing the System

Download the System Image

Only use the image provided in bigtreetech/CB2/releases

Write System to MicroSD Card

  1. Download the balenaEtcher software from balena.io/etcher, install, and run it.

  2. Insert the MicroSD card via a card reader.

  3. Select your downloaded image.

  4. Select the MicroSD card and click "Flash" (WRITE the image will format the MicroSD card. Be careful not to select the wrong storage device, otherwise the data will be formatted).

  5. Wait for the process to complete.

Writing System onto eMMC

Using RKDevTool (Windows) to Write the eMMC

Download and unzip RKDevTool.zip from the GitHub repo bigtreetech/CB2 to your computer. DO NOT insert a MicroSD card.

  1. Turn the DIP switch 4 (USBOTG) and 3 (RPIBOOT) to the ON position to enter BOOT mode.

  2. Then, connect the Type-C cable to the computer.

  3. Install the driver:

    1. In “Device Manager”, if you see “Unknown Device”, it indicates that the computer is missing drivers.

    2. Open the DriverAssistant tool in the downloaded RKDevTool folder, click “①Uninstall Driver”, then click “② Install Driver” to ensure that the latest version of the driver is installed.

    3. After the installation is complete, hold down the “Recovery” button, replug the Type-C cable. "Device Manager" should now recognize a “Rockusb Device”, indicating that the driver installation is successful.

  4. Open the “RKDevTool” software:

    Note

    The parameters in the software are set by default as shown in the image. Normally, you only need to set the “4 actual path of the .img system”. If the parameters in your software do not match those in the image, manually adjust them to match.

    1. Find the path where the downloaded RKDevTool is located.

    2. Open the RKDevTool tool.

    3. The software will recognize a “LOADER” or “MASKROOM” device.

    4. Select the system to be written (the OS image must be unzipped as a .img file beforehand; RKDevTool does not support directly writing compressed .xz files).

    5. Check “Write by Address”.

    6. Click “Run” to start writting the system.

    7. “Download image OK” indicates that the system has been successfully burned.

  5. After writing is complete, toggle the USB OTG switch to the OFF position to boot normally. Note: Files on the eMMC cannot be accessed by the computer like those on a MicroSD card, so you cannot modify the system.cfg configuration file to set up the WiFi network. Instead, use an Ethernet cable or USB-to-UART connection to configure the terminal.

Writing System onto eMMC Using a MicroSD Card

  1. First, write the system onto the MicroSD card. Then, insert the MicroSD card into the motherboard's card slot and wait for the system to boot.

  2. Connect to the system terminal via Ethernet cable, WiFi, or USB to UART, and log in to the system.

    CB2 image minimal username and password

    login as: root
password: root

    CB2 image with Klipper username and password

    login as: biqu
password: biqu

    root account

    login as: root
password: root

Execute the command sudo nand-sata-install. In the interface that pops up, select 2 Boot From eMMC - system on eMMC and then select OK

  1. Select "Yes" to start erasing and writing the system onto the eMMC.

  2. Choose the filesystem "1 ext4" and then select "OK".

  3. Wait for the writing process to complete.

  4. Upon completion, you will be prompted whether to power off. Select “Power off” to shut down the system.

  5. After the system has powered down, disconnect the power supply, remove the MicroSD card, and then reconnect power. The system should now boot from the eMMC.

Erasing eMMC

When using a MicroSD card as the system card instead, it's best to erase the data on the eMMC to prevent the motherboard from booting from it by mistake.

Using RKDevTool (Windows) to Erase eMMC

  1. Refer to the steps in Using RKDevTool to Write the eMMC (Windows) to connect the motherboard to the computer.

  2. Open the RKDevTool.

    1. Find the path where the downloaded RKDevTool is located.

    2. Open the RKDevTool.

    3. The software will recognize a LOADER device. If it recognizes MASKROOM, it indicates there is no data in the eMMC, hence no erase operation is necessary.

    4. Click Advanced Function.

    5. Click EraseAll to begin erasing data from the eMMC.

    6. Erasing sectors success indicates the erasure is complete.

Erasing eMMC After Booting from MicroSD Card

  1. Refer to the steps in Writing System onto eMMC Using a MicroSD Card and log into the system terminal.

  2. Run the command sudo mkfs /dev/mmcblk1 and then enter y to confirm.

System Configuration

Using Ethernet

Ethernet is plug-and-play and requires no additional setup.

Setting Up WiFi

After the system image has been written, the MicroSD card will have a FAT32 partition recognized by the computer. In this partition, there is a system.cfg file. Open it and replace Your SSID with your actual WiFi name and Your Password with the actual password.

Configuring Overlays

Open the armbianEnv.txt file in the BOOT partition and set the values for overlays. The configurati on file supports only one line of overlays at a time; if multiple overlays are enabled, only the last line will take effect. If you need multiple overlays, place the contents of multiple configurations on the same line separated by a space. For example, if you need to use a DSI screen, MCP2515 SPI to CAN module, and I2C1 simultaneously

overlays=dsi mcp2515 i2c1

Configuring the Display

  1. Open the "armbianEnv.txt" file in the BOOT partition.

  2. The default overlay is set to "hdmi," meaning the system uses an HDMI screen by default. This can be changed to match the actual screen being used, such as:

  3. hdmi: HDMI screen

  4. dsi: DSI screen

  5. tft_35: SPI Screen

For tft_35, there is also a tft35_spi_rotate parameter for system-level screen rotation, with default "0" meaning no rotation, other options include 90, 180, 270.

Note

Only one screen type can be used at a time.

  1. To configure KlipperScreen, open the system.cfg file in the BOOT partition. Set the screen type with the parameter ks_src, and the rotation angle with ks_angle.

Using SPI to CAN

Open the armbianEnv.txt file in the BOOT partition and add mcp2515 to the overlays configuration.

Using CSI Camera and Crowsnest Configuration

For both RPi v1.3 ov5647 and RPi v2 imx219 cameras, no specific configuration in "armbianEnv.txt" is required as they are plug-and-play. "crowsnest.conf" file configuration is as follows:

device: /dev/video0
# The CSI camera node is fixed as video0

custom_flags: --format=UYVY
# The current system's CSI camera does not support the default YUYV, so it needs to be set to the supported UYVY format.

Using Bluetooth

  1. To scan for Bluetooth devices, enter the following command, and a list of Bluetooth devices will appear as shown below:

    bluetoothctl --timeout 15 scan on

  2. Find your Bluetooth device, for example, if your device name is "HONOR xSport PRO", locate the corresponding Bluetooth MAC ID as shown below.

  3. To connect to a Bluetooth device, enter the following command, connection success is shown as below

    bluetoothctl connect E0:9D:FA:50:CD:4F

    1. If there's an issue while connecting, as shown below, please restart the Bluetooth device and repeat steps 1 and 2 to connect.

    2. If there's an issue while connecting, as shown below, please enter the following commands and then repeat steps 1 and 2:

      bluetoothctl remove E0:9D:FA:50:CD:4F # Your Bluetooth device's corresponding MAC ID
rfkill block bluetooth
sleep 3s
rfkill unblock bluetooth
pulseaudio -k
pulseaudio –start

  4. If you exit voice playback during the use of Bluetooth and cannot reuse it, manually delete the corresponding playback process. Use the ps command to view the process number, then use kill -9 <process_number> to delete the corresponding playback process.

Setting up 3.5mm Headphones Port

  1. Enter the command: 

    aplay -l

Check for the corresponding sound card, as shown in the image (the sound card for the headphone port shown in the image corresponds to card 0).

  1. Enter the command:

    amixer -c 0 contents # 0 represents the card 0 found in the previous `aplay -l` command

    Check the settings for playback and recording channels, as shown in the image.

  2. Enter the command:

    amixer -c 0 cset numid=1 3

    Set the playback channel, as shown in the image.

  3. Enter the command:

    amixer -c 0 cset numid=2 1

    Set the recording channel, as shown in the image.

  4. Enter the following command to play audio, with the audio file directory xxx and the audio file name xxxxx.wav:

aplay -D plughw:0,0 /path/to/file.wav
  1. Enter the following command to record (where 10 represents recording for 10 seconds), storing the recording in directory /path/to/, file name file.wav.
sudo arecord -Dhw:0,0 -d 10 -f cd -r 44100 -c 2 -t wav /path/to/file.wav
  1. Enter the following command to play the recording:
aplay -D plughw:0,0 /path/to/file.wav

SSH Connect to Device

SSH Application

Install the ssh application Mobaxterm: https://mobaxterm.mobatek.net/download-home-edition.html

  1. After powering on, wait for the system to boot, which typically takes about 1 to 2 minutes.

  2. Once the device is connected to WiFi or an Ethernet cable is plugged in, it will automatically be assigned an IP address.

  3. Access the router management interface to find the device's IP (it should be BTT-CB2 here).

  4. Open Mobaxterm and click "Session", and click "SSH", inset the device IP into Remote host and click "OK" (Note: your computer and the device needs to be in the same network).

  5. Login as: biqu password: biqu

Precautions

Boot from eMMC

When booting from eMMC, do not insert a MicroSD card. When booting from a MicroSD card, it is necessary to erase the data in the eMMC.

  1. About 10 seconds after powering on, the system enters the kernel phase. At this time, the blue light stays on, and the green light flashes continuously, indicating that the system is running normally.

  2. user account

    login in as biqu
    login as: biqu
password: biqu
    login in as root
    login as: root
password: root

  3. The PCIe M.2 interface does not support hot-plugging; the solid-state drive must be connected in advance for the device to be recognized.