SystemCoreClock variable holds HCLK frequency and is defined in system_stm32f4xx.c file. Each time the core clock (HCLK) changes, user had to update SystemCoreClock variable value. Otherwise, any configuration based on this variable will be incorrect. This variable is updated in three ways: 1) by calling CMSIS function SystemCoreClockUpdate() 2) by calling HAL API function HAL_RCC_GetSysClockFreq() 3) each time HAL_RCC_ClockConfig() is called to configure the system clock frequency 翻译

SystemCoreClock变量保存了HCLK频率，它在system_stm32f4xx.c文件中被定义。每当核心时钟(HCLK)发生变化时，用户必须更新SystemCoreClock变量的值，否则基于此变量的任何配置都将不正确。有三种方式更新此变量：1)通过调用CMSIS函数SystemCoreClockUpdate()；2)通过调用HAL API函数HAL_RCC_GetSysClockFreq()；3)每次调用HAL_RCC_ClockConfig()来配置系统时钟频率时都会更新此变量。

相关问题

In this exercise you will create a program to read text from standard input and write it to a file with each line prefixed with a line-number count. This file will be specified by a command-line argument. Directions Create a program called TestLineNumbering that accepts one command-line argument, the name of a file. Your code should verify that the command-line argument was specified. Declare a variable that holds a File object that is initialized from the file named in the first command-line argument. Within a try-catch block, create a buffered, input stream reader based on the System.in stream (standard input). Also, create a print file writer based on the File variable. Write the while loop that reads each line from the console input stream and prints the line out to the file. Each line should be prepended with the count of the line number. Make sure to close the I/O streams.

Here is a possible solution in Java:

import java.io.*;

public class TestLineNumbering {

    public static void main(String[] args) {
        if (args.length != 1) {
            System.err.println("Usage: java TestLineNumbering <output-file>");
            System.exit(1);
        }
        String fileName = args[0];
        try {
            File outputFile = new File(fileName);
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            PrintWriter writer = new PrintWriter(outputFile);
            String line;
            int lineNumber = 0;
            while ((line = reader.readLine()) != null) {
                writer.printf("%d: %s%n", ++lineNumber, line);
            }
            writer.close();
            reader.close();
        } catch (IOException e) {
            System.err.println("Error: " + e.getMessage());
            System.exit(2);
        }
    }

}

The program checks that exactly one command-line argument is provided, which is the name of the output file. It then creates a `BufferedReader` to read from standard input, and a `PrintWriter` to write to the output file. The program reads each line from standard input, increments a line number counter, and writes the line with the line number prefix to the output file. Finally, the I/O streams are closed, and any exceptions are caught and reported.

os.environ['PATH'] = os.environ['PATH'] + ';' + dir_path + '/../../x64/Release;' + dir_path + '/../../bin;'

This line of code sets the environment variable PATH to include two new directories:

- dir_path/../../x64/Release
- dir_path/../../bin

The semicolon (;) is used as a separator between different directories in the PATH variable.

Assuming that dir_path is a variable that holds the path of the current working directory, this code is trying to add two new directories to the PATH variable, which could be useful if there are executables or libraries located in those directories that need to be accessed by the current Python script.