Supported MCUs


Peripheral Support

The following list indicates peripherals supported in NuttX:







































































  • CONFIG_RAM_SIZE - Describes the installed DRAM (SRAM in this case)

  • CONFIG_RAM_START - The start address of installed DRAM


  • CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt stack. If defined, this symbol is the size of the interrupt stack in bytes. If not defined, the user task stacks will be used during interrupt handling.


  • CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG - Enables special STM32 clock configuration features.:

  • CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation of delay loops


Timer devices may be used for different purposes. One special purpose is to generate modulated outputs for such things as motor control. If CONFIG_STM32_TIMn is defined (as above) then the following may also be defined to indicate that the timer is intended to be used for pulsed output modulation, ADC conversion, or DAC conversion. Note that ADC/DAC require two definition: Not only do you have to assign the timer (n) for used by the ADC or DAC, but then you also have to configure which ADC or DAC (m) it is assigned to.

  • CONFIG_STM32_TIMn_PWM Reserve timer n for use by PWM, n=1,..,14

  • CONFIG_STM32_TIMn_ADC Reserve timer n for use by ADC, n=1,..,14

  • CONFIG_STM32_TIMn_ADCm Reserve timer n to trigger ADCm, n=1,..,14, m=1,..,3

  • CONFIG_STM32_TIMn_DAC Reserve timer n for use by DAC, n=1,..,14

  • CONFIG_STM32_TIMn_DACm Reserve timer n to trigger DACm, n=1,..,14, m=1,..,2

For each timer that is enabled for PWM usage, we need the following additional configuration settings:

  • CONFIG_STM32_TIMx_CHANNEL - Specifies the timer output channel {1,..,4}

NOTE: The STM32 timers are each capable of generating different signals on each of the four channels with different duty cycles. That capability is not supported by this driver: Only one output channel per timer.



  • CONFIG_STM32_JTAG_NOJNTRST_ENABLE - Enables full SWJ (JTAG-DP + SW-DP) but without JNTRST.

  • CONFIG_STM32_JTAG_SW_ENABLE - Set JTAG-DP disabled and SW-DP enabled


  • CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=1,2,3) or UART m (m=4,5) for the console and ttys0 (default is the USART1).

  • CONFIG_U[S]ARTn_RXBUFSIZE - Characters are buffered as received. This specific the size of the receive buffer

  • CONFIG_U[S]ARTn_TXBUFSIZE - Characters are buffered before being sent. This specific the size of the transmit buffer

  • CONFIG_U[S]ARTn_BAUD - The configure BAUD of the UART. Must be

  • CONFIG_U[S]ARTn_BITS - The number of bits. Must be either 7 or 8.

  • CONFIG_U[S]ARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity

  • CONFIG_U[S]ARTn_2STOP - Two stop bits


  • CONFIG_CAN - Enables CAN support (one or both of CONFIG_STM32_CAN1 or CONFIG_STM32_CAN2 must also be defined)

  • CONFIG_CAN_EXTID - Enables support for the 29-bit extended ID. Default Standard 11-bit IDs.

  • CONFIG_CAN_FIFOSIZE - The size of the circular buffer of CAN messages. Default: 8

  • CONFIG_CAN_NPENDINGRTR - The size of the list of pending RTR requests. Default: 4

  • CONFIG_CAN_LOOPBACK - A CAN driver may or may not support a loopback mode for testing. The STM32 CAN driver does support loopback mode.

  • CONFIG_STM32_CAN1_BAUD - CAN1 BAUD rate. Required if CONFIG_STM32_CAN1 is defined.

  • CONFIG_STM32_CAN2_BAUD - CAN1 BAUD rate. Required if CONFIG_STM32_CAN2 is defined.

  • CONFIG_STM32_CAN_TSEG1 - The number of CAN time quanta in segment 1. Default: 6

  • CONFIG_STM32_CAN_TSEG2 - the number of CAN time quanta in segment 2. Default: 7

  • CONFIG_STM32_CAN_REGDEBUG - If CONFIG_DEBUG_FEATURES is set, this will generate an dump of all CAN registers.


  • CONFIG_STM32_SPI_INTERRUPTS - Select to enable interrupt driven SPI support. Non-interrupt-driven, poll-waiting is recommended if the interrupt rate would be to high in the interrupt driven case.

  • CONFIG_STM32_SPIx_DMA - Use DMA to improve SPIx transfer performance. Cannot be used with CONFIG_STM32_SPI_INTERRUPT.


  • CONFIG_SDIO_DMA - Support DMA data transfers. Requires CONFIG_STM32_SDIO and CONFIG_STM32_DMA2.

  • CONFIG_STM32_SDIO_PRI - Select SDIO interrupt priority. Default: 128

  • CONFIG_STM32_SDIO_DMAPRIO - Select SDIO DMA interrupt priority. Default: Medium

  • CONFIG_STM32_SDIO_WIDTH_D1_ONLY - Select 1-bit transfer mode. Default: 4-bit transfer mode.


STM32 USB OTG FS Host Driver Support


  • CONFIG_USBHOST - Enable general USB host support

  • CONFIG_STM32_OTGFS - Enable the STM32 USB OTG FS block

  • CONFIG_STM32_SYSCFG - Needed

  • CONFIG_STM32_OTGFS_RXFIFO_SIZE - Size of the RX FIFO in 32-bit words. Default 128 (512 bytes)

  • CONFIG_STM32_OTGFS_NPTXFIFO_SIZE - Size of the non-periodic Tx FIFO in 32-bit words. Default 96 (384 bytes)

  • CONFIG_STM32_OTGFS_PTXFIFO_SIZE - Size of the periodic Tx FIFO in 32-bit words. Default 96 (384 bytes)

  • CONFIG_STM32_OTGFS_DESCSIZE - Maximum size of a descriptor. Default: 128

  • CONFIG_STM32_OTGFS_SOFINTR - Enable SOF interrupts. Why would you ever want to do that?

  • CONFIG_STM32_USBHOST_REGDEBUG - Enable very low-level register access debug. Depends on CONFIG_DEBUG_FEATURES.

  • CONFIG_STM32_USBHOST_PKTDUMP - Dump all incoming and outgoing USB packets. Depends on CONFIG_DEBUG_FEATURES.

LTDC hardware acceleration

The LTDC driver provides two 2 LTDC overlays and supports the following hardware acceleration and features:

Configured at build time:

  • background color

  • default color (outside visible screen)

Configurable by nuttx framebuffer interface:

  • cmap support (color table is shared by both LTDC overlays and DMA2D when enabled)

Configurable via the nuttx framebuffer interface (for each layer separately):

  • chromakey

  • transparency (const alpha and pixel alpha)

  • blank

  • color (if DMA2D is enabled and cmap is disabled)

  • blit (if DMA2D is enabled)

  • blend (if DMA2D is enabled and cmap is disabled)

LTDC overlays are similar to a non-destructive overlay. Both LTDC overlays will be permanently blended in the order (background -> overlay 0 -> overlay 1) and converted to a resulting video signal by the LTDC controller. That means each operation with a LTDC overlay (Overlay 0 and Overlay 1) via nuttx framebuffer interface will be visible immediately. Think about continuous blending between both overlays.

DMA2D hardware acceleration

The DMA2D driver implements the following hardware acceleration:

Configurable via the nuttx framebuffer interface:

  • cmap support (color table is shared by all DMA2D overlays and LTDC overlays)

Configurable via the nuttx framebuffer interface (for each layer separately):

  • color (fill memory region with a specific ARGB8888 color immediately), if cmap is disabled

  • blit (copy memory region to another memory region with pixel format conversion if necessary)

  • blend (blend two memory regions and copy the result to a third memory region with pixel format conversion if necessary), if cmap is disabled

Blit and blend operation using a fixes memory size defined by the background layer. DMA2D controller doesn’t support scaling.

DMA2D overlays are similar to destructive overlays. They are invisible. They can be used for image preprocessing. The memory region affected by the operations (color, blit, blend) can be addressed by the area control command before. The configured overlay transparency of DMA2D overlays will be used for subsequently blend operation and is valid for the whole overlay.


FPU Configuration Options

There are two version of the FPU support built into the STM32 port.

  1. Non-Lazy Floating Point Register Save

    In this configuration floating point register save and restore is implemented on interrupt entry and return, respectively. In this case, you may use floating point operations for interrupt handling logic if necessary. This FPU behavior logic is enabled by default with:

  2. Lazy Floating Point Register Save.

    An alternative implementation only saves and restores FPU registers only on context switches. This means: (1) floating point registers are not stored on each context switch and, hence, possibly better interrupt performance. But, (2) since floating point registers are not saved, you cannot use floating point operations within interrupt handlers.

    This logic can be enabled by simply adding the following to your .config file:


Development Environment

Either Linux or Cygwin on Windows can be used for the development environment. The source has been built only using the GNU toolchain (see below). Other toolchains will likely cause problems.

GNU Toolchain Options

Toolchain Configurations

The NuttX make system has been modified to support the following different toolchain options.

  1. The NuttX buildroot Toolchain (see below), or

  2. Any generic arm-none-eabi GNU toolchain.

All testing has been conducted using the NuttX Codesourcery toolchain. To use a different toolchain, you simply need to modify the configuration. As an example:

CONFIG_ARM_TOOLCHAIN_GNU_EABI : Generic arm-none-eabi toolchain


NuttX is built using command-line make. It can be used with an IDE, but some effort will be required to create the project.

Makefile Build

Under Eclipse, it is pretty easy to set up an “empty makefile project” and simply use the NuttX makefile to build the system. That is almost for free under Linux. Under Windows, you will need to set up the “Cygwin GCC” empty makefile project in order to work with Windows (Google for “Eclipse Cygwin” - there is a lot of help on the internet).

Using Sourcery CodeBench from Download and install the latest version (as of this writing it was sourceryg++-2013.05-64-arm-none-eabi)

Import the project from git. File->import->Git-URI, then import a Exiting code as a Makefile progject from the working directory the git clone was done to.

Select the Sourcery CodeBench for ARM EABI. N.B. You must do one command line build, before the make will work in CodeBench.

Native Build

Here are a few tips before you start that effort:

  1. Select the toolchain that you will be using in your .config file

  2. Start the NuttX build at least one time from the Cygwin command line before trying to create your project. This is necessary to create certain auto-generated files and directories that will be needed.

  3. Set up include paths: You will need include/, arch/arm/src/stm32, arch/arm/src/common, arch/arm/src/armv7-m, and sched/.

  4. All assembly files need to have the definition option -D __ASSEMBLY__ on the command line.

Startup files will probably cause you some headaches. The NuttX startup file is arch/arm/src/stm32/stm32_vectors.S. With RIDE, I have to build NuttX one time from the Cygwin command line in order to obtain the pre-built startup object needed by RIDE.

NuttX EABI “buildroot” Toolchain

A GNU GCC-based toolchain is assumed. The PATH environment variable should be modified to point to the correct path to the Cortex-M3 GCC toolchain (if different from the default in your PATH variable).

If you have no Cortex-M3 toolchain, one can be downloaded from the NuttX Bitbucket download site ( This GNU toolchain builds and executes in the Linux or Cygwin environment.

NXFLAT Toolchain

If you are not using the NuttX buildroot toolchain and you want to use the NXFLAT tools, then you will still have to build a portion of the buildroot tools – just the NXFLAT tools. The buildroot with the NXFLAT tools can be downloaded from the NuttX Bitbucket download site (

This GNU toolchain builds and executes in the Linux or Cygwin environment.

  1. You must have already configured NuttX in <some-dir>/nuttx.

    tools/ lpcxpresso-lpc1768:<sub-dir>

  2. Download the latest buildroot package into <some-dir>

  3. unpack the buildroot tarball. The resulting directory may have versioning information on it like buildroot-x.y.z. If so, rename <some-dir>/buildroot-x.y.z to <some-dir>/buildroot.

  4. cd <some-dir>/buildroot

  5. cp boards/cortexm3-defconfig-nxflat .config

  6. make oldconfig

  7. make

  8. Make sure that the PATH variable includes the path to the newly built

    NXFLAT binaries.

Protected Mode Build

The “protected” mode build uses the Cormtex-M4 MPU to separate the FLASH and SRAM into kernel-mode and user-mode regions. The kernel mode regions are then protected from any errant or mischievous behavior from user-space applications.

Common notes for all protected mode builds follow:

  1. It is recommends to use a special make command; not just ‘make’ but make with the following two arguments:

    make pass1 pass2

    In the normal case (just ‘make’), make will attempt to build both user- and kernel-mode blobs more or less interleaved. That actual works! However, for me it is very confusing so I prefer the above make command: Make the user-space binaries first (pass1), then make the kernel-space binaries (pass2)

  2. At the end of the build, there will be several files in the top-level NuttX build directory:

      nuttx_user.elf    - The pass1 user-space ELF file
      nuttx_user.hex    - The pass1 Intel HEX format file (selected in defconfig)          - Symbols in the user-space ELF file
      nuttx             - The pass2 kernel-space ELF file
      nuttx.hex         - The pass2 Intel HEX file (selected in defconfig)        - Symbols in the kernel-space ELF file
    The J-Link programmer will except files in .hex, .mot, .srec, and .bin
  3. Combining .hex files. If you plan to use the .hex files with your debugger or FLASH utility, then you may need to combine the two hex files into a single .hex file. Here is how you can do that.

    1. The ‘tail’ of the nuttx.hex file should look something like this (with my comments added):

        $ tail nuttx.hex
        # 00, data records
        :10 9DC0 00 01000000000800006400020100001F0004
        :10 9DD0 00 3B005A0078009700B500D400F300110151
        :08 9DE0 00 30014E016D0100008D
        # 05, Start Linear Address Record
        :04 0000 05 0800 0419 D2
        # 01, End Of File record
        :00 0000 01 FF
      Use an editor such as vi to remove the 05 and 01 records.
    2. The ‘head’ of the nuttx_user.hex file should look something like

      this (again with my comments added):

      $ head nuttx_user.hex
      # 04, Extended Linear Address Record
      :02 0000 04 0801 F1
      # 00, data records
      :10 8000 00 BD89 01084C800108C8110208D01102087E
      :10 8010 00 0010 00201C1000201C1000203C16002026
      :10 8020 00 4D80 01085D80010869800108ED83010829

      Nothing needs to be done here. The nuttx_user.hex file should be fine.

    3. Combine the edited nuttx.hex and un-edited nuttx_user.hex file to produce a single combined hex file:

      $ cat nuttx.hex nuttx_user.hex >combined.hex

    Then use the combined.hex file with the to write the FLASH image. With GDB this would be:

    gdb> mon reset
    gdb> mon halt
    gdb> mon clrbp
    gdb> load combined.hex

    If you do this a lot, you will probably want to invest a little time to develop a tool to automate these steps.

Supported Boards