RT thread analysis log system RT_ Kprintf analysis

Catalog

1 Preface

2 rt_kprintf()

3 configuration option

4 console equipment

4.1 Equipment declaration

4.2 Device creation

4.3 obtain _console_device

5 analysis rt_kprintf() function

6 rt_kprintf Redirect

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1 Preface

         In addition to providing interfaces rt_kprintf() Used to output print information , It also supports a complete set of logging components ulog. There is overlap between the two in implementation , All used console modular ; Other functions are independent of each other , Only by studying its implementation mechanism , In order to better use or transplant the system .

2 rt_kprintf()

• The kernel provides an interface for outputting log information
• By default console Device output printing , The device name can be modified in the configuration options
• If not registered console equipment ,rt_kprintf Will eventually call rt_hw_console_output() Output printing ; This function is for users to realize functions

3 configuration option

Use this interface , The following configuration is required before compilation

• It mainly determines the following two parameters

// Print cache length 
#define RT_CONSOLEBUF_SIZE 256
// Console device name 
#define RT_CONSOLE_DEVICE_NAME "uart2"

4 console equipment

        rt_kprintf() System default use console The device outputs print information , All you need to know is how to create and use the kernel sonsole equipment

4.1 Equipment declaration

         The kernel uses global variables _console_device To maintain the console equipment

static rt_device_t _console_device = RT_NULL;

4.2 Device creation

• In the startup process , The kernel calls rt_hw_usart_init() complete uart Device registration ;
• And then call rt_console_set_device(RT_CONSOLE_DEVICE_NAME), Go to the registered device to find out whether there is a device with the name RT_CONSOLE_DEVICE_NAME The equipment , If so, regard the device as _console_device

4.3 obtain _console_device

• External unified call rt_console_get_device() To get _console_device

rt_device_t rt_console_get_device(void)
{
    return _console_device;
}

5 analysis rt_kprintf() function

RT_WEAK void rt_kprintf(const char *fmt, ...)
{
    //1  Cache declaration , Note that static local variables , Maximum length is RT_CONSOLEBUF_SIZE
    static char rt_log_buf[RT_CONSOLEBUF_SIZE];
    
    va_start(args, fmt);
    //2  Sort out the print log and save it to rt_log_buf, And return the actual output length 
    length = rt_vsnprintf(rt_log_buf, sizeof(rt_log_buf) - 1, fmt, args);
    
    //3  Limit length 
    if (length > RT_CONSOLEBUF_SIZE - 1)
        length = RT_CONSOLEBUF_SIZE - 1;
        
    if (_console_device == RT_NULL)
    {
        //4  If the kernel is not registered console equipment , execute rt_hw_console_output() Complete output .
        rt_hw_console_output(rt_log_buf);
    }
    else
    {
        //5  Use it directly console Device output information 
        rt_device_write(_console_device, 0, rt_log_buf, length);
    }
    
    va_end(args);
}

6 rt_kprintf Redirect

• You can use the reserved rt_hw_console_output() Interface .
• Do not register console equipment , in rt_hw_console_output() Complete redirection
• Or will console Register as any device , Like Ethernet ,CAN,USB etc.