The dprintf implementation in LK

In LK we usually print the log through dprintf, as shown below
dprintf (INFO, "0x%x", T->tls[i]);
where info represents the level of log, LK has three levels in total
/* Debug Levels */
#define CRITICAL 0
#define ALWAYS 0
#define INFO 1
#define SPEW 2


Continue to see the realization of dprintf
#define DPRINTF (level, x ...) do {if (level) <= debuglevel) {_dprintf (x);}} while (0)
found that if you want to print a level smaller than debuglevel,log it will be printed
#if defined (DEBUG)
#define DebugLevel DEBUG
#else
#define DEBUGLEVEL 2
#endif
You can see that if debug is not defined, DebugLevel defaults to 2, which means that all logs can be printed.
The implementation of _DPRINTF is as follows:
int _dprintf (const char *FMT, ...)
{
Char buf[256];
Char ts_buf[13];
int err;


snprintf (ts_buf, sizeof (TS_BUF), "[%u]", current_time ());
Dputs (always, ts_buf);


Va_list ap;
Va_start (AP, FMT);
Call vsnprintf to format the string, such as the 0x%x in this example to indicate that the log is printed in 16 binary ways
Err = vsnprintf (buf, sizeof (BUF), FMT, AP);
Va_end (AP);


Dputs (always, buf);


return err;
}
Log is specifically called Dputs to print out, we continue to see its implementation
#define DPUTS (level, str) does {if (level) <= debuglevel) {_dputs (str);}} and (0)




To the above, but also to determine the log level, continue to call _dputs to print log,_dputs is the implementation of the specific platform, we look at an example that has been implemented.
int _dputs (const char *STR)
{
while (*str! = 0) {
_DPUTC (*str++);
}


return 0;
}
The characters in a string are printed through _DPUTC by a while loop.
void _dputc (char c)
{
*reg8 (debug_stdout) = C;
}
#define REG8 (addr) ((volatile uint8_t *) (addr))
As you can see, the HW will automatically print the characters as soon as the string is written to the UART register.