rt-thread/libcpu/arm/cortex-m4/README.md

Independent Interrupts Management

Introduction

Calling rt_hw_interrupt_disable in multiple places on rt-thread may cause interruption delays when the application requires accurate interrupt responses. This is because the system cannot generate any interrupts except abnormal interrupts after disabling interrupts. This is a common problem in the interrupt management of the operating system. The independent interrupt management module is designed to solve this problem.

The independent interrupt management module is designed to solve the problem of interrupt delays caused by calling rt_hw_interrupt_disable in multiple places on rt-thread. The module is implemented by rewrite the rt_hw_interrupt_disable and rt_hw_interrupt_enable functions in the libcpu library.

Usage

• Add the following code to the project's board.c file.

  #ifdef RT_USING_INDEPENDENT_INTERRUPT_MANAGEMENT
  #define RT_NVIC_PRO_BITS    __NVIC_PRIO_BITS
  
  rt_base_t rt_hw_interrupt_disable(void)
  {
  rt_base_t level = __get_BASEPRI();
  __set_BASEPRI(RT_MAX_SYSCALL_INTERRUPT_PRIORITY << (8 - RT_NVIC_PRO_BITS));
  
  __ISB();
  __DSB();
  
  return level;
  }
  
  void rt_hw_interrupt_enable(rt_base_t level)
  {
  __set_BASEPRI(level);
  }
  
  #endif /* RT_USING_INDEPENDENT_INTERRUPT_MANAGEMENT */
  

• Add the following configuration to the Kconfig file in the board directory.

  menuconfig RT_USING_INDEPENDENT_INTERRUPT_MANAGEMENT
      bool "Enable independent interrupt management"
      default n
  
      if RT_USING_INDEPENDENT_INTERRUPT_MANAGEMENT
          config RT_MAX_SYSCALL_INTERRUPT_PRIORITY
              int "Set max syscall interrupt priority"
              range 0 7
              default 2
      endif
  

• Select RT_USING_INDEPENDENT_INTERRUPT_MANAGEMENT to enable this feature.

• Select RT_MAX_SYSCALL_INTERRUPT_PRIORITY to set the maximum priority of the interrupt that can be called by the system call. The default value is 2.

Description

• The basepri register is used in the functions to complete the interrupt management.
• For example, if RT_MAX_SYSCALL_INTERRUPT_PRIORITY is set to 0x01, the system masking only interrupts with a priority of 0x01-0xFF.
• Interrupts with a priority of 0 are not managed by the system and can continue to respond to interrupts after rt_hw_interrupt_disable is called.
• When using the basepri register for independent interrupt management, note that interrupts with a priority value lower than RT_MAX_SYSCALL_INTERRUPT_PRIORITY cannot call any system API.