Zoltan Hudak / Mbed OS Blackpill_Hello

Using low cost Blackpill (STM32F411CEU6) boards with mbed.

Using Blackpill (STM32F401CCU6 or STM32F411CEU6) boards with mbed

It provides an affordable (about $3 / $6 on eBay) and flexible way for users to try out new ideas and build prototypes. The board is equipped with an STM32F401CCU6 or an STM32F411CEU6 microcontroller compatible with the NUCLEO-F401CE or the NUCLEO-F411RE platform, respectively.

Microcontroller features

• STM32F401CCU6 or STM32F411CEU6 in UFQFPN48 package
• ARM® 32-bit Cortex® -M4 CPU with FPU
• 100 MHz max CPU frequency
• VDD from 1.7 V to 3.6 V
• 256 or 512 KB Flash
• 64KB or 128 KB SRAM
• GPIO with external interrupt capability
• 1x12-bit, 2.4 MSPS ADC with 16 channels
• DMA Controller
• Up to 11 Timers (six 16-bit, two 32-bit, two watchdog timers and a SysTick timer)
• USART/UART (3)
• I2C (3)
• SPI/I2S (3 or 5)
• SDIO
• USB 2.0 full-speed device/host/OTG controller with on-chip PHY
• CRC calculation unit
• 96-bit unique ID
• RTC

Board features

• Small foot-print
• Flexible board power supply: USB VBUS or external source (3.3V, 5V)
• User LED: LED1
• Three push buttons: RESET, BOOT0, KEY
• Programming/Debug port
• USB-C connector
  
  

Board pinout

When equipped with STM32F401CCU6:

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When equipped with STM32F411CEU6:

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For more details on pin definitions see Table 8 in the Datasheet.

Using the mbed online compiler to build programs for the Blackpill board

Create a program as if it was for a NUCLEO-F401RE or NUCLEO-F411RE board (select NUCLEO-F401RE or NUCLEO-F411RE as target platform for the online compiler).
Or click here to import this demo into your online compiler.

#include "mbed.h"

DigitalOut led(PC_13);

int main()
{
    while (true) {
        led = !led;
        ThisThread::sleep_for(500ms);
    }
}

Building programs with Mbed Studio IDE

The Mbed Studio IDE is a great tool for working offline.

• It supports Mbed OS 6 (with built-in Mbed RTOS threads, mutexes, semafores ...)

• and also Mbed OS 6 Bare metal profile (no RTOS, similar to Mbed OS 2) which is suitable for small or medium size projects requiring less RAM and Flash. To use it, add a mbed_app.json configuration file to your project:

{
    "requires": ["bare-metal"]
}

As target you can select

• either the NUCLEO_F401RE or the NUCLEO_F411RE

• or the BLACKPILL custom target.

Advantages of the BLACKPILL custom target over the NUCLEO_F401RE/ NUCLEO_F411RE

• The onboard external 25 MHz crystal is used as system clock source rather than the less precise internal 16 MHz RC oscillator.

• The onboard LED works as LED1 in programs.

• The onboard KEY on STM32F411CEU6 boards works as USER_BUTTON pin in programs.

• You can use the USB peripheral in your programs and connect the board to the PC over the onboard USB connector. An example of using the USB peripheral as USBSerial (12 Mbit/s) is available here.

Building programs for the BLACKPILL custom target in Mbed Studio

• Connect an STM32 ST-Link programmer to your BLACKPILL board and PC (see below for more details).

• Create a new program in the Mbed Studio IDE.

• Right-click on the program's root folder and in the popup window select Add library...

• Copy&paste the text https://os.mbed.com/users/hudakz/code/BLACKPILL_Custom_Target into the Git or os.mbed.com URL edit box and click on the Next button.

• Open the drop-list and select default as Branch or tag and click on the Finish button.

• Open the BLACKPILL_Custom_Target folder and according to you board drag&drop the TARGET_BLACKPILL_F401CC or the TARGET_BLACKPILL_F411CE folder and the custom_targets.json file one by one to the root folder of your program.

• Delete the BLACKPILL_Custom_Target folder from your project. (Right-click and select delete).

• Open the Target drop-list and click on the button with a "chip" icon on it (Manage custom targets) .

• Open the USB device drop-list and select your STM32 ST-Link programmer.

• Open the Build target drop-list and according to your board select BLACKPILL_F401CC or BLACKPILL_F411CE.

• Click on the Save All button.

• Build your program (click on hammer button).
  
  

Programming the Blackpill board

NUCLEO ST-LINK/V2-1 and drag & drop

You can use the NUCLEO virtual disk to program the Blackpii board (drag and drop programming). To do that, an additional NUCLEO board is needed (any type equipped with ST-LINK/V2-1 will do).

• Remove the two jumpers from the CN2 connector as illustrated in Figure 8:
  
  

• Connect the NUCLEO board CN4 connector to the Blackpill board using flying wires as follows:

• Provide power for the Blackpill board through a 3.3V pin, 5V pin or over a USB cable. (The VDD_TARGET pin on the NUCLEO board CON4 does not work as source of power).
  
  
• Connect the NUCLEO board to your PC over a USB cable.
  
  
• To program the Blackpill board, click on the Compile button and save the binary to the NUCLEO virtual disk .
  For more details have a look at the User Manual, chapter 6.2.4 Using ST-LINK/V2-1 to program and debug an external STM32 application.
  
  

ST-Link V2 USB dongle and STM32 ST-LINK utility

If you would like to use an ST-Link V2 USB dongle (aka ST-Link V2 Programming Unit) to program the board apply the same wiring as specified above. If not done yet install an ST-Link/V2 driver onto your PC. Plug the ST-Link V2 dongle into your PC. Then click on the Compile button and save the binary to your local disk. Install and run the STM32 ST-LINK utility. Once the program is running open the binary built with the online compiler and click on the Program verify button.

STM32 USART system memory bootloader and Flasher-STM32

Have a look at STM32 Embedded Bootloader.

Download: FLASHER-STM32
For more details read: Appliction Note AN2606.

Using serial port (not just for debugging)

• Connect an FTDI or similar USB to Serial TTL converter to your PC and to an on-board serial port (for example PA_2, PA_3). Make sure you connect the on-board TX pin to the converter's RX pin and the on-board RX pin to the converter's TX pin.

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• In your code, create a Serial object (using TX and RX pin names of the connected serial port).

• Use printf function to send serial messages to the connected PC.
  
  

#include "mbed.h" 

// declarations needed to change the parameters of stdio UART 
extern serial_t     stdio_uart; 
extern int          stdio_uart_inited; 

int main() {
    serial_init(&stdio_uart, PA_9, PA_10); // other than Serial2
    stdio_uart_inited = 1; 
    printf("Ready for debugging\r\n");
}

Happy coding :-)