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The functions __enable_irq and __disable_irq are optimized for quickly enabling and disabling all interrupts globally by directly manipulating the PRIMASK register, typically requiring only a few CPU cycles.
__disable_irq() is implemented as CPSID I, which turns off all exceptions which can have a priority set (those configured in the NVIC), it achieves this by changing the PRIMASK register (setting bit 0) within the CPU. There is no way to tell this to only enable a specific interrupt.
I am working on a project with an STM32f446 and I need to disable all interrupts while executing a specific critical function. I put in my code the following lines : __disable_irq (); Critical_function (); __enable_irq (); But I still get interrupt while critical_function is executed.
Each ARM-core microcontroller manufacturer, I believe, including STM32 types, must define and create its own list of IRQn_Type interrupt request types, so see below for the STM32 details on their specific interrupt types defined for each MCU.
To avoid problems like this, the idea is that before you disable interrupts in your function, first check interrupt enabled status in Cortex-M4 PRIMASK register to see if they were enabled or disabled before.
__disable_irq() disables all interrupts, with the exception of a few non-maskable ones, preventing interrupt handlers from running as a result of stimuli such as timers, pin changes, incoming I/O, etc.
Disable IRQ Interrupts Disables IRQ interrupts by setting special-purpose register PRIMASK. Can only be executed in Privileged modes.
It supports cases when you want to keep certain high-priority interrupts enabled, and mask the rest of interrupts at once. Basically it simplifies separation of interrupt sources to "real-time" and "less real-time". A well known example of using PRIMASK is FreeRTOS.
It does not seem to be true (indeed previos interrupt mask is restored), but it does explain why the suggested way to leave the critical section is by __enable_irq().
It appears the errors come about because of missing header files under system_stm32f10x.c/stm32f10x.h. It took me a long time to figure out how to "correct" for the error and I had to change: