From 8249e71bcccffc8d4e96b32178f1e40863656ccf Mon Sep 17 00:00:00 2001
From: Evlers <1425295900@qq.com>
Date: Thu, 29 Aug 2024 11:00:40 +0800
Subject: [PATCH] add readme files

---
 libcpu/arm/cortex-m4/README.md | 53 ++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 libcpu/arm/cortex-m4/README.md

diff --git a/libcpu/arm/cortex-m4/README.md b/libcpu/arm/cortex-m4/README.md
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+## 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](https://developer.arm.com/documentation/107706/0100/Exceptions-and-interrupts-overview/Special-registers-for-exception-masking/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](https://developer.arm.com/documentation/107706/0100/Exceptions-and-interrupts-overview/Special-registers-for-exception-masking/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`.