96Boards Carbon


Zephyr applications use the 96b_carbon configuration to run on the 96Boards Carbon hardware. It is based on the STMicroelectronics STM32F401RET Cortex-M4 CPU and also contains a nRF51822 chip connected over SPI for BLE connectivity.

The 96Boards Carbon board is built with two chips: an STMicroelectronics STM32F401RET Cortex-M4 CPU and an nRF51822 chip connected to the Cortex-M4 CPU over SPI for Bluetooth LE connectivity. Even though both chips exist on the same physical board, they must be programmed separately:

  • The 96b_carbon configuration is used when developing programs for the main chip on the board, the STM32F401RET. Users will likely want to write applications targeting this chip, using the 96b_carbon configuration, since it is connected to all of the breakout I/O headers.
  • The 96b_carbon_nrf51 configuration should be used for programming the secondary nRF51822 chip. Most users will likely not develop applications for this chip, since Zephyr already provides a sample application that can be flashed onto the nRF51822 to provide Bluetooth functionality to applications on the main STM32F401RET chip.

For instructions on how to set up the nRF51822 to develop Bluetooth applications, see Providing Bluetooth to 96b_carbon.

After you have flashed your nRF51, you can perform basic validation of this Bluetooth setup using the instructions below.

96Boards Carbon

96Boards Carbon


96Boards Carbon provides the following hardware components:

  • STM32F401RET6 in LQFP64 package
  • ARM® 32-bit Cortex®-M4 CPU with FPU
  • 84 MHz max CPU frequency
  • VDD from 1.7 V to 3.6 V
  • 512 KB Flash
  • 96 KB SRAM
  • GPIO with external interrupt capability
  • 12-bit ADC with 16 channels
  • RTC
  • Advanced-control Timer
  • General Purpose Timers (7)
  • Watchdog Timers (2)
  • USART/UART (4)
  • I2C (3)
  • SPI (3)
  • SDIO
  • USB 2.0 OTG FS
  • DMA Controller
  • Bluetooth LE over SPI, provided by nRF51822
More information about STM32F401RE can be found here:

Supported Features

The Zephyr 96b_carbon board configuration supports the following hardware features:

Interface Controller Driver/Component
NVIC on-chip nested vector interrupt controller
SYSTICK on-chip system clock
UART on-chip serial port
GPIO on-chip gpio
PINMUX on-chip pinmux
FLASH on-chip flash
SPI on-chip spi
I2C on-chip i2c
USB OTG FS on-chip USB device

More details about the board can be found at 96Boards website.

The default configuration can be found in the defconfig file:


Connections and IOs


  • LED1 / User1 LED = PD2
  • LED2 / User2 LED = PA15
  • LED3 / BT LED = PB5
  • LED4 / Power LED = VCC

Push buttons

  • BUTTON = BOOT0 (SW1)

External Connectors

Low Speed Header

PIN # Signal Name STM32F401 Functions
13 AIN12 PC2
15 AIN14 PC4
21 I2C1_SCL PB6
23 I2C1_SCA PB7
25 I2C2_SCA PB3
27 I2C2_SCL PB10
PIN # Signal Name STM32F401 Functions
2 SPI2_SS PB12
12 VCC2 VCC2
14 AIN13 PC3
16 AIN15 PC5
22 I2C1_SCL PB8
24 I2C1_SDA PB9
26 AIN10 PC0
28 AIN11 PC1
30 NC NC

External Clock Sources

STM32F4 has two external oscillators. The frequency of the slow clock is 32.768 kHz. The frequency of the main clock is 16 MHz.

Serial Port

96Boards Carbon board has up to 4 U(S)ARTs. The Zephyr console output is assigned to USART1. Default settings are 115200 8N1.


96Boards Carbon board has up to 2 I2Cs. The default I2C mapping for Zephyr is:

  • I2C1_SCL : PB6
  • I2C1_SDA : PB7
  • I2C2_SCL : PB10
  • I2C2_SDA : PB3


96Boards Carbon board has up to 2 SPIs. SPI1 is used for Bluetooth communication over HCI. The default SPI mapping for Zephyr is:

  • SPI1_NSS : PA4
  • SPI1_SCK : PA5
  • SPI1_MISO : PA6
  • SPI1_MOSI : PA7
  • SPI2_NSS : PB12
  • SPI2_SCK : PB13
  • SPI2_MISO : PB14
  • SPI2_MOSI : PB15


96Boards Carbon board has a USB OTG dual-role device (DRD) controller that supports both device and host functions through its mini “OTG” USB connector. Only USB device functions are supported in Zephyr at the moment.

  • USB_DM : PA11
  • USB_DP : PA12

Programming and Debugging

There are 2 main entry points for flashing STM32F4X SoCs, one using the ROM bootloader, and another by using the SWD debug port (which requires additional hardware). Flashing using the ROM bootloader requires a special activation pattern, which can be triggered by using the BOOT0 pin. The ROM bootloader supports flashing via USB (DFU), UART, I2C and SPI. You can read more about how to enable and use the ROM bootloader by checking the application note AN2606, page 109.


Installing dfu-util

It is recommended to use at least v0.8 of dfu-util. The package available in debian/ubuntu can be quite old, so you might have to build dfu-util from source.

Flashing an Application to 96Boards Carbon

Connect the micro-USB cable to the USB OTG Carbon port and to your computer. The board should power ON. Force the board into DFU mode by keeping the BOOT0 switch pressed while pressing and releasing the RST switch.

Confirm that the board is in DFU mode:

$ sudo dfu-util -l
dfu-util 0.8
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2014 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to [email protected]
Found DFU: [0483:df11] ver=2200, devnum=15, cfg=1, intf=0, alt=3, name="@Device Feature/0xFFFF0000/01*004 e", serial="3574364C3034"
Found DFU: [0483:df11] ver=2200, devnum=15, cfg=1, intf=0, alt=2, name="@OTP Memory /0x1FFF7800/01*512 e,01*016 e", serial="3574364C3034"
Found DFU: [0483:df11] ver=2200, devnum=15, cfg=1, intf=0, alt=1, name="@Option Bytes /0x1FFFC000/01*016 e", serial="3574364C3034"
Found DFU: [0483:df11] ver=2200, devnum=15, cfg=1, intf=0, alt=0, name="@Internal Flash /0x08000000/04*016Kg,01*064Kg,03*128Kg", serial="3574364C3034"
Found Runtime: [05ac:8290] ver=0104, devnum=2, cfg=1, intf=5, alt=0, name="UNKNOWN", serial="UNKNOWN"

You should see following confirmation on your Linux host:

$ dmesg
usb 1-2.1: new full-speed USB device number 14 using xhci_hcd
usb 1-2.1: New USB device found, idVendor=0483, idProduct=df11
usb 1-2.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-2.1: Product: STM32 BOOTLOADER
usb 1-2.1: Manufacturer: STMicroelectronics
usb 1-2.1: SerialNumber: 3574364C3034

Then build and flash an application. Here is an example for the Hello World application.

# On Linux/macOS
cd $ZEPHYR_BASE/samples/hello_world
mkdir build && cd build

# On Windows
cd %ZEPHYR_BASE%\samples\hello_world
mkdir build & cd build

# Use cmake to configure a Ninja-based build system:
cmake -GNinja -DBOARD=96b_carbon ..

# Now run ninja on the generated build system:
ninja flash

Connect the micro-USB cable to the USB UART (FTDI) port and to your computer. Run your favorite terminal program to listen for output.

$ minicom -D <tty_device> -b 115200

Replace <tty_device> with the port where the board 96Boards Carbon can be found. For example, under Linux, /dev/ttyUSB0. The -b option sets baud rate ignoring the value from config.

Press the Reset button and you should see the the following message in your terminal:

Hello World! arm

Verifying Bluetooth Functionality

This section contains instructions for verifying basic Bluetooth functionality on the board. For help on Zephyr applications in general, see Build an Application.

  1. Flash the nRF51 with the hci_spi sample application as described in Providing Bluetooth to 96b_carbon.

  2. Install the dfu-util flashing app, as described above.

  3. Build and flash the samples/bluetooth/ipsp application for 96b_carbon. See the instructions above for how to put your board into DFU mode if you haven’t done this before:

    # On Linux/macOS
    cd $ZEPHYR_BASE/samples/bluetooth/ipsp
    mkdir build && cd build
    # On Windows
    cd %ZEPHYR_BASE%\samples\bluetooth\ipsp
    mkdir build & cd build
    # Use cmake to configure a Ninja-based build system:
    cmake -GNinja -DBOARD=96b_carbon ..
    # Now run ninja on the generated build system:
    ninja flash
  1. Refer to the instructions in Bluetooth: IPSP Sample for how to verify functionality.

Congratulations! Your 96Boards Carbon now has Bluetooth connectivity. Refer to Bluetooth for additional information on further Bluetooth application development.


The 96b_carbon can be debugged by installing a 100 mil (0.1 inch) header into the header at the bottom right hand side of the board, and attaching an SWD debugger to the 3V3 (3.3V), GND, CLK, DIO, and RST pins on that header. Then apply power to the 96Boards Carbon via one of its USB connectors. You can now attach your debugger to the STM32F401RET using an SWD scan.