readline函数分析

函数功能:提示用户输入命令，并读取命令
/****************************************************************************/

/*
* Prompt for input and read a line.
* If CONFIG_BOOT_RETRY_TIME is defined and retry_time >= 0,
* time out when time goes past endtime (timebase time in ticks).
* Return: number of read characters
* -1 if break
* -2 if timed out
*/
int readline (const char *const prompt)
{
#ifdef CONFIG_CMDLINE_EDITING
char *p = console_buffer;
unsigned int len=MAX_CMDBUF_SIZE;
int rc;
static int initted = 0;

if (!initted) {
hist_init();
initted = 1;
}

puts (prompt);

rc = cread_line(p, &len);
return rc < 0 ? rc : len;
#else
char *p = console_buffer; // console_buffer是作为读取命令的缓冲区
int n = 0; /* buffer index */
int plen = 0; /* prompt length */
int col; /* output column cnt */
char c;

/* print prompt */
if (prompt) { //如果提示符非零，就输出提示符
plen = strlen (prompt);
puts (prompt);
}
col = plen;

for (;;) {
#ifdef CONFIG_BOOT_RETRY_TIME
while (!tstc()) { /* while no incoming data */
if (retry_time >= 0 && get_ticks() > endtime)
return (-2); /* timed out */
}
#endif
WATCHDOG_RESET(); /* Trigger watchdog, if needed */

#ifdef CONFIG_SHOW_ACTIVITY
while (!tstc()) {
extern void show_activity(int arg);
show_activity(0);
}
#endif
c = getc(); //从串口读取一个字符

/*
* Special character handling
*/
switch (c) {
case '\r': /* Enter */
case '\n':
*p = '\0';
puts ("\r\n");
return (p - console_buffer);//返回输入命令的长度

case '\0': /* nul */
continue;

case 0x03: /* ^C - break */ //终止输入
console_buffer[0] = '\0'; /* discard input */
return (-1);

case 0x15: /* ^U - erase line */
while (col > plen) {
puts (erase_seq);
--col;
}
p = console_buffer;
n = 0;
continue;

case 0x17: /* ^W - erase word */
p=delete_char(console_buffer, p, &col, &n, plen);
while ((n > 0) && (*p != ' ')) {
p=delete_char(console_buffer, p, &col, &n, plen);
}
continue;

case 0x08: /* ^H - backspace */
case 0x7F: /* DEL - backspace */ //删除操作
p=delete_char(console_buffer, p, &col, &n, plen);
continue;

default:
/*
* Must be a normal character then
*/
if (n < CFG_CBSIZE-2) {
if (c == '\t') { /* expand TABs */
#ifdef CONFIG_AUTO_COMPLETE //自动补全功能
/* if auto completion triggered just continue */
*p = '\0';
if (cmd_auto_complete(prompt, console_buffer, &n, &col)) {
p = console_buffer + n; /* reset */
continue;
}
#endif
puts (tab_seq+(col&07));
col += 8 - (col&07);
} else {
++col; /* echo input */ //打印出输入的命令
putc (c);
}
*p++ = c; /*把字符保存在buffer中*/
++n;
} else { /* Buffer full */
putc ('\a');
}
}
}
#endif /* CONFIG_CMDLINE_EDITING */
}

参考：U-Boot启动第二阶段代码分析