ST STM32L Discovery

This page discusses issues unique to NuttX configurations for the STMicro STM32L-Discovery development board. The STM32L-Discovery board is based on the STM32L152RBT6 MCU (128KB FLASH and 16KB of SRAM).

The STM32L-Discovery and 32L152CDISCOVERY kits are functionally equivalent. The difference is the internal Flash memory size (STM32L152RBT6 with 128 Kbytes or STM32L152RCT6 with 256 Kbytes).

Both boards feature:

  • An ST-LINK/V2 embedded debug tool interface,

  • LCD (24 segments, 4 commons),

  • LEDs,

  • Pushbuttons,

  • A linear touch sensor, and

  • Four touchkeys.

LEDs

The STM32L-Discovery board has four LEDs. Two of these are controlled by logic on the board and are not available for software control:

LD1 COM:   LD2 default status is red. LD2 turns to green to indicate
           that communications are in progress between the PC and the
           ST-LINK/V2.
LD2 PWR:   Red LED indicates that the board is powered.

And two LEDs can be controlled by software:

User LD3:  Green LED is a user LED connected to the I/O PB7 of the
           STM32L152 MCU.
User LD4:  Blue LED is a user LED connected to the I/O PB6 of the
           STM32L152 MCU.

These LEDs are not used by the board port unless CONFIG_ARCH_LEDS is defined. In that case, the usage by the board port is defined in include/board.h and src/stm32_autoleds.c. The LEDs are used to encode OS-related events as follows:

SYMBOL

Meaning

LED3

LED4

LED_STARTED

NuttX has been started

OFF

OFF

LED_HEAPALLOCATE

Heap has been allocated

OFF

OFF

LED_IRQSENABLED

Interrupts enabled

OFF

OFF

LED_STACKCREATED

Idle stack created

ON

OFF

LED_INIRQ

In an interrupt

N/C

N/C

LED_SIGNAL

In a signal handler

N/C

N/C

LED_ASSERTION

An assertion failed

N/C

N/C

LED_PANIC

The system has crashed

OFF

Blinking

LED_IDLE

STM32 is is sleep mode

N/U

Serial Console

The STM32L-Discovery has no on-board RS-232 driver. Further, there are no USART pins that do not conflict with the on board resources, in particular, the LCD: Most USART pins are available if the LCD is enabled; USART2 may be used if either the LCD or the on-board LEDs are disabled.

PA9 USART1_TX LCD glass COM1 P2, pin 22 PA10 USART1_RX LCD glass COM2 P2, pin 21 PB6 USART1_TX LED Blue P2, pin 8 PB7 USART1_RX LED Green P2, pin 7

PA2 USART2_TX LCD SEG1 P1, pin 17 PA3 USART2_RX LCD SEG2 P1, pin 18

PB10 USART3_TX LCD SEG6 P1, pin 22 PB11 USART3_RX LCD SEG7 P1, pin 23 PC10 USART3_TX LCD SEG22 P2, pin 15 PC11 USART3_RX LCD SEG23 P2, pin 14

NOTES:

  • GND and (external) 5V are available on both P1 and P2. Note: These signals may be at lower voltage levels and, hence, may not properly drive an external RS-232 transceiver.

  • The crystal X3 is not installed on the STM32L3-Discovery. As a result, the HSE clock is not available and the less accurate HSI must be used. This may limit the accuracy of the computed baud, especially at higher BAUD. The HSI is supposedly calibrated in the factory to within 1% at room temperatures so perhaps this not a issue.

  • According to the STM32L-Discovery User Manual, the LCD should be removed from its socket if you use any of the LCD pins for any other purpose.

    I have had no problems using the USART1 with PA9 and PA10 with a 3.3-5V RS-232 transceiver module at 57600 baud. I have not tried higher baud rates.

  • There is no support for a USB serial connector on the STM32L-Discovery board. The STM32L152 does support USB, but the USB pins are “free I/O” on the board and no USB connector is provided. So the use of a USB console is not option. If you need console output, you will need to disable either LCD (and use any USART) or the LEDs (and use USART1)

Debugging

If you are going to use a debugger, you should make sure that the following settings are selection in your configuration file:

CONFIG_DEBUG_SYMBOLS=y     : Enable debug symbols in the build
CONFIG_ARMV7M_USEBASEPRI=y : Use the BASEPRI register to disable interrupts

OpenOCD

I am told that OpenOCD will work with the ST-Link, but I have never tried it.

This is an open source server for the ST-Link that I have never used.

Configurations

Each STM32L-Discovery configuration is maintained in a sub-directory and can be selected as follow:

tools/configure.sh STM32L-Discovery:<subdir>

Where <subdir> is one of the following sub-directories.

NOTE: These configurations use the mconf-based configuration tool. To change any of these configurations using that tool, you should:

  1. Build and install the kconfig-mconf tool. See nuttx/README.txt see additional README.txt files in the NuttX tools repository.

  2. Execute ‘make menuconfig’ in nuttx/ in order to start the reconfiguration process.

Configuration sub-directories

nsh:

Configures the NuttShell (nsh) located at apps/examples/nsh.

NOTES:

  1. The serial console is on UART1 and NuttX LED support is enabled. Therefore, you will need an external RS232 driver or TTL serial-to- USB converter. The UART1 TX and RX pins should be available on PA9 and PA10, respectively.

    The serial console is configured for 57600 8N1 by default.

  2. Support for NSH built-in applications is not enabled.

  3. By default, this configuration uses the ARM EABI toolchain for Windows and builds under Cygwin (or probably MSYS). That can easily be reconfigured, of course.

    Build Setup:

        CONFIG_HOST_WINDOWS=y                   : Builds under Windows
    CONFIG_WINDOWS_CYGWIN=y                 : Using Cygwin

System Type::

    CONFIG_ARM_TOOLCHAIN_GNU_EABI=y      : GNU EABI toolchain for Windows

  4. SLCD. When the LCD is enabled and the LEDs are disabled, the USART1 serial console will automatically move to PB6 and PB7 (you will get a compilation error if you forget to disable the LEDs).

    SIGNAL

    FUNCTION

    LED

    CONNECTION

    PB6

    USART1_TX

    LED Blue

    P2, pin 8

    PB7

    USART1_RX

    LED Green

    P2, pin 7

    To enable apps/examples/slcd to test the SLCD:

    Binary Formats:

    CONFIG_BINFMT_DISABLE=n                 : Don't disable binary support
CONFIG_BUILTIN=y                        : Enable support for built-in binaries

    Application Configuration -> NSH Library:

    CONFIG_NSH_BUILTIN_APPS=y               : Enable builtin apps in NSH
CONFIG_NSH_ARCHINIT=y                   : Needed to initialize the SLCD

    Application Configuration -> Examples:

    CONFIG_EXAMPLES_SLCD=y                  : Enable apps/examples/slcd