STM32 Nucleo standard

Status: draft, see issue 19296.

This page collects the rules that all STM32 Nucleo boards in NuttX follow. It starts with the common board initialization and grows as more of the board logic becomes shared.

Serial console

The default console of every Nucleo board is the USART wired to the ST-LINK virtual COM port, so a board works over its USB cable without any extra wiring. The pins of that USART are always defined in the board board.h, not only when a board Kconfig console choice selects them, so a configuration that bypasses the board Kconfig (for example a custom board build pointing at the board directory) only needs to enable the USART and select it as the console. Other console wirings (Arduino or Morpho headers) stay optional choices.

Common board initialization

Initialization that does not depend on the board lives in boards/arm/common/stm32/src/board_common.c. It is part of the common STM32 board logic (CONFIG_ARCH_BOARD_COMMON), which every Nucleo board selects, and provides one function:

#include "board_common.h"

int stm32_common_initialize(void);

Every Nucleo board calls stm32_common_initialize() early in its bringup, in stm32_bringup() or, if the board has none, in board_late_initialize(). A failure is logged and the bringup continues.

The function currently handles:

Feature	Enabled by	Result
procfs	`CONFIG_FS_PROCFS`	mounted at `CONFIG_NSH_PROC_MOUNTPOINT` or `/proc`
tmpfs	`CONFIG_FS_TMPFS`	mounted at `CONFIG_LIBC_TMPDIR`
IWDG	`CONFIG_STM32_IWDG`	`/dev/watchdog0`
WWDG	`CONFIG_STM32_WWDG`	`/dev/watchdog1`
CAN	`CONFIG_STM32_CAN_CHARDRIVER` `CONFIG_STM32_FDCAN_CHARDRIVER`	`/dev/can0`, `/dev/can1`, … in instance order
SocketCAN	`CONFIG_STM32_CAN_SOCKET` `CONFIG_STM32_FDCAN_SOCKET`	interfaces for all enabled instances
I2C	`CONFIG_I2C_DRIVER`	`/dev/i2cN` for every enabled `CONFIG_STM32_I2CN`

The file systems are not mounted when CONFIG_DISABLE_MOUNTPOINT is set. The IWDG uses STM32_LSI_FREQUENCY from the board board.h.

Timers

Timer and oneshot devices are registered from one option per instance, N being the TIM or LPTIM instance number:

Option	Device
`CONFIG_BOARD_STM32_COMMON_TIMn_TIMER`	`/dev/timerN`
`CONFIG_BOARD_STM32_COMMON_TIMn_ONESHOT`	`/dev/oneshotN`
`CONFIG_BOARD_STM32_COMMON_LPTIMn_TIMER`	`/dev/lptimerN`
`CONFIG_BOARD_STM32_COMMON_LPTIMn_ONESHOT`	`/dev/lponeshotN`

The options need CONFIG_TIMER or CONFIG_ONESHOT (a TIM oneshot also CONFIG_STM32_ONESHOT) and the CONFIG_STM32_TIMn or CONFIG_STM32_LPTIMn instance. An instance is either a timer or a oneshot. A TIM oneshot counts in microseconds. An LPTIM counts on its kernel clock, STM32_LPTIMn_CLKIN in the board board.h.

Rules for boards:

Do not repeat any of the features above in the board directory.
Board-independent initialization is added to stm32_common_initialize(), not to individual boards.
board.h defines STM32_LPTIMn_CLKIN for every LPTIM instance of the chip.