Add a new variant (board)

What is a variant?

It is described by Arduino here

A core variant folder is an additional folder that is compiled together with the core and allows platform developers to easily add specific configurations.

Variants must be placed inside the variants folder in the current architecture.

Since STM32 core release 2.0.0 variants folder contains one folder for each STM32 MCU family.

Variants folders

Each MCU family has several MCU references. Each subfolder name can contain one or more mcu reference(s).

STM32G0xx family example

MCU name are factorized to avoid long path names, for example:

G0B1R(B-C-E)T_G0C1R(C-E)T is for G0B1RBT, G0B1RCT, G0B1RET, G0C1RCT and G0C1RET.

All generic variants are now automatically generated in the variant folder thanks the STM32_open_pin_data repository which provides all the information required for the pin configuration of products based on STM32 MCU.

This means that the generic STM32 MCU files required for a variant are generated inside each MCU folder. Only the linker script is not automatically generated. Note that the default system clock configuration is empty by default. So the default clock at reset will be used.

Generated variant files

Warning

Below files are automatically generated so do not modify them. Only the generic_clock.c can be modified to add default system clock configuration and so will not be overwritten.

board_entry.txt: contains generic variant declaration to ease board addition in the boards.txt file. See Arduino boards.txt specification.
generic_clock.c: contains the default system clock configuration: WEAK void SystemClock_Config(void)
PinNamesVar.h: contains specific PinName definitions of the MCU
PeripheralPins.c: contains list of available PinName per peripheral.
variant_generic.cpp: contains Digital PinName array and Analog (`Ax) [pin number] array
variant_generic.h: contains all definition required by the variant: STM32 [pin number] definitions, peripheral pins for default instances: Serial, I2C, SPI, Tone, Servo, ...

Tip

The example of all the steps below are available in this PR: Add generic G0B1R(B-C-E)T, G0C1R(C-E)T and Nucleo-G0B1RE

Define a new generic variant

Before adding a specific board, it is a good practice to add the generic entry of the STM32 MCU as it is possible to use it with the specific board.

Note

A folder name can reference several MCU references so several boards entry could be added. Not only the one of the specific board.

1 - Find the MCU folder

Go to the variants folder of the STM32 core (See Where are sources).

Example: To add variant for the Nucleo-G0B1RE search for the folder name including G0B1RET reference in the STM32G0xx subfolder of the variants folder. In this case:

G0B1R(B-C-E)T_G0C1R(C-E)T

Several files are present as stated here. It misses only the default linker script named ldscript.ld.

2 - Add the default linker script

It could be generated thanks STM32CubeMX.

Open STM32CubeMX then create a New Project and select the targeted MCU. In this example the STM32G0B1RET:

Create new CubeMX project...

Configure the project thanks the Project Manager tab:

Set a project name
Set a project location
Select the IDE: STM32CubeIDE

Configure the project...

Generate the code by clicking on _ Generate Code_ button and open the folder

Generate the project...

Copy the STM32YYxxxxxx_FLASH.ld generated by STM32CubeMX in the variant folder and rename it: ldscript.ld

Example for the Nucleo-G0B1RE: STM32G0B1RETX_FLASH.ld

In order to have a common linker script for all MCU the RAM and FLASH definitions have to be updated. As the linker script is preprocessed it is possible to use some definitions based on board entry and defined by the platform.txt.

-Wl,--defsym=LD_FLASH_OFFSET={build.flash_offset} -Wl,--defsym=LD_MAX_SIZE={upload.maximum_size} -Wl,--defsym=LD_MAX_DATA_SIZE={upload.maximum_data_size}

LD_FLASH_OFFSET: Flash base offset mainly used when a custom bootloader is used. Default set to 0.
LD_MAX_DATA_SIZE: RAM size
LD_MAX_SIZE: Flash size

Edit the ldscript.ld file accordingly:

 /* Memories definition */
 MEMORY
 {
-  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 144K
-  FLASH    (rx)    : ORIGIN = 0x8000000,   LENGTH = 512K
+  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = LD_MAX_DATA_SIZE
+  FLASH    (rx)    : ORIGIN = 0x8000000 + LD_FLASH_OFFSET, LENGTH = LD_MAX_SIZE - LD_FLASH_OFFSET
 }

3 - Generic System Clock configuration

generic_clock.c contains the default system clock configuration which is empty by default. So the default clock at reset will be used as stated by the warning:

WEAK void SystemClock_Config(void)
{
  /* SystemClock_Config can be generated by STM32CubeMX */
#warning "SystemClock_Config() is empty. Default clock at reset is used."
}

Important

For generic board the internal clock is used: HSI.

STM32CubeMX is also used to generate it.

Go to Pinout tab, enable the desired peripherals which require specific clock configuration (not needed for peripherals clocked by HCLKx, or APBx clock): SDIO, USB, ... In this example only USB needs to be enabled as other peripherals default clock are correct by default.

Pinout configuration...

Configure the clock:
- Set PLL Source Mux to HSI.
- Try to set the CPU clock and HCLK to the maximum frequencies, STM32CubeMX will automatically configure the clock tree and resolve conflict if any. Sometimes due to some constraints (ex: USB) maximum frequency is not reachable.
Generate the code by clicking on _ Generate Code_ button and open the folder

Generate the project...

In the generic_clock.c replace the body of the SystemClock_Config(void) by the one generated in src/main.c of the generated project.

Example

 WEAK void SystemClock_Config(void)
 {
-  /* SystemClock_Config can be generated by STM32CubeMX */
-#warning "SystemClock_Config() is empty. Default clock at reset is used."
+  RCC_OscInitTypeDef RCC_OscInitStruct = {};
+  RCC_ClkInitTypeDef RCC_ClkInitStruct = {};
+  RCC_PeriphCLKInitTypeDef PeriphClkInit = {};
+
+  /** Configure the main internal regulator output voltage
+  */
+  HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1);
+  /** Initializes the RCC Oscillators according to the specified parameters
+  * in the RCC_OscInitTypeDef structure.
+  */
+  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI | RCC_OSCILLATORTYPE_HSI48;
+  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
+  RCC_OscInitStruct.HSI48State = RCC_HSI48_ON;
+  RCC_OscInitStruct.HSIDiv = RCC_HSI_DIV1;
+  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
+  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
+  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
+  RCC_OscInitStruct.PLL.PLLM = RCC_PLLM_DIV1;
+  RCC_OscInitStruct.PLL.PLLN = 8;
+  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
+  RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;
+  RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;
+  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
+    Error_Handler();
+  }
+  /** Initializes the CPU, AHB and APB buses clocks
+  */
+  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_SYSCLK
+                                | RCC_CLOCKTYPE_PCLK1;
+  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
+  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
+  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
+
+  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK) {
+    Error_Handler();
+  }
+  /** Initializes the peripherals clocks
+  */
+  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB;
+  PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_HSI48;
+  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK) {
+    Error_Handler();
+  }
 }

Tip

Pay attention to the default value of HAL RCC structures. CubeMx set it to 0 but it produces warning. Simply remove the 0 like this:

-  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
-  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
+  RCC_OscInitTypeDef RCC_OscInitStruct = {};
+  RCC_ClkInitTypeDef RCC_ClkInitStruct = {};

4 - Declare the variant

It is still to add the menu and add relevant information (Flash and SRAM sizes, ...)

Tip

See Arduino boards.txt specification for further options.

Edit boards.txt file, then:

Find the menu part where to add the generic entry. In this example the GenG0 menu.
Copy all the boards entry from the board_entry.txt file to this section. Pay attention to alphabetical order.
Check if the build.product_line= is correct and match the STM32YYXXxx MCU version.
Check the upload.maximum_size= and upload.maximum_data_size=

Example

 GenG0.menu.pnum.GENERIC_G081RBTX.build.variant=STM32G0xx/G071R(6-8)T_G071RB(I-T)_G081RB(I-T)
 
+# Generic G0B1RBTx
+GenG0.menu.pnum.GENERIC_G0B1RBTX=Generic G0B1RBTx
+GenG0.menu.pnum.GENERIC_G0B1RBTX.upload.maximum_size=131072
+GenG0.menu.pnum.GENERIC_G0B1RBTX.upload.maximum_data_size=147456
+GenG0.menu.pnum.GENERIC_G0B1RBTX.build.board=GENERIC_G0B1RBTX
+GenG0.menu.pnum.GENERIC_G0B1RBTX.build.product_line=STM32G0B1xx
+GenG0.menu.pnum.GENERIC_G0B1RBTX.build.variant=STM32G0xx/G0B1R(B-C-E)T_G0C1R(C-E)T
+
+# Generic G0B1RCTx
+GenG0.menu.pnum.GENERIC_G0B1RCTX=Generic G0B1RCTx
+GenG0.menu.pnum.GENERIC_G0B1RCTX.upload.maximum_size=262144
+GenG0.menu.pnum.GENERIC_G0B1RCTX.upload.maximum_data_size=147456
+GenG0.menu.pnum.GENERIC_G0B1RCTX.build.board=GENERIC_G0B1RCTX
+GenG0.menu.pnum.GENERIC_G0B1RCTX.build.product_line=STM32G0B1xx
+GenG0.menu.pnum.GENERIC_G0B1RCTX.build.variant=STM32G0xx/G0B1R(B-C-E)T_G0C1R(C-E)T
+
+# Generic G0B1RETx
+GenG0.menu.pnum.GENERIC_G0B1RETX=Generic G0B1RETx
+GenG0.menu.pnum.GENERIC_G0B1RETX.upload.maximum_size=524288
+GenG0.menu.pnum.GENERIC_G0B1RETX.upload.maximum_data_size=147456
+GenG0.menu.pnum.GENERIC_G0B1RETX.build.board=GENERIC_G0B1RETX
+GenG0.menu.pnum.GENERIC_G0B1RETX.build.product_line=STM32G0B1xx
+GenG0.menu.pnum.GENERIC_G0B1RETX.build.variant=STM32G0xx/G0B1R(B-C-E)T_G0C1R(C-E)T
+
+# Generic G0C1RCTx
+GenG0.menu.pnum.GENERIC_G0C1RCTX=Generic G0C1RCTx
+GenG0.menu.pnum.GENERIC_G0C1RCTX.upload.maximum_size=262144
+GenG0.menu.pnum.GENERIC_G0C1RCTX.upload.maximum_data_size=147456
+GenG0.menu.pnum.GENERIC_G0C1RCTX.build.board=GENERIC_G0C1RCTX
+GenG0.menu.pnum.GENERIC_G0C1RCTX.build.product_line=STM32G0C1xx
+GenG0.menu.pnum.GENERIC_G0C1RCTX.build.variant=STM32G0xx/G0B1R(B-C-E)T_G0C1R(C-E)T
+
+# Generic G0C1RETx
+GenG0.menu.pnum.GENERIC_G0C1RETX=Generic G0C1RETx
+GenG0.menu.pnum.GENERIC_G0C1RETX.upload.maximum_size=524288
+GenG0.menu.pnum.GENERIC_G0C1RETX.upload.maximum_data_size=147456
+GenG0.menu.pnum.GENERIC_G0C1RETX.build.board=GENERIC_G0C1RETX
+GenG0.menu.pnum.GENERIC_G0C1RETX.build.product_line=STM32G0C1xx
+GenG0.menu.pnum.GENERIC_G0C1RETX.build.variant=STM32G0xx/G0B1R(B-C-E)T_G0C1R(C-E)T
+
 # Upload menu

5 - Add new reference to the `README.md`

Finally, all the new reference have to be added in the README.md

Example

 | :green_heart: | STM32G081RB | Generic Board | *2.0.0* |  |
+| :yellow_heart: | STM32G0B1RB<br>STM32G0B1RC<br>STM32G0B1RE | Generic Board | **2.1.0** |  |
+| :yellow_heart: | STM32G0C1RB<br>STM32G0C1RE | Generic Board | **2.1.0** |  |
 
 ### Generic STM32G4 boards

6 - Restart

Restart Arduino IDE and try one of the new entry with the CheckVariant example.

Important

An issue with the Arduino IDE 2.x prevents the board to appears in the menu. Follow this workaround to get it working: https://github.com/arduino/arduino-ide/issues/1030#issuecomment-1152005617

Define a specific board

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Add a new variant (board)

What is a variant?

Generated variant files

Define a new generic variant

1 - Find the MCU folder

2 - Add the default linker script

3 - Generic System Clock configuration

4 - Declare the variant

5 - Add new reference to the `README.md`

6 - Restart

Define a specific board

Clone this wiki locally

Add a new variant (board)

What is a variant?

Generated variant files

Define a new generic variant

1 - Find the MCU folder

2 - Add the default linker script

3 - Generic System Clock configuration

4 - Declare the variant

5 - Add new reference to the README.md

6 - Restart

Define a specific board

Clone this wiki locally

5 - Add new reference to the `README.md`