1、printk
level的打印级别
在printk.h中定义了8个级别的log level，
#define KERN_EMERG "<0>"
#define KERN_ALERT "<1>"
#define KERN_CRIT "<2>"
#define KERN_ERR "<3>"
#define KERN_WARNING "<4>"
#define KERN_NOTICE "<5>"
#define KERN_INFO "<6>"
#define KERN_DEBUG "<7>"
内核中关于printk level的定义：在kernel/printk文件
/* printk's without a loglevel use this.. */
#define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
/* We show everything that is MORE important than this.. */
#define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
int console_printk[4] = {
DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */ 终端级别
DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */默认级别
MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */让用户使用的最小级别
DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */默认终端级别
};
查看printk打印级别的方法：
sh-# cat /proc/sys/kernel/printk
7 4 1 7
设定printk level的两种办法：
(1)使用dmesg命令进行设定，
sh-# cat /proc/sys/kernel/printk
0 4 1 7
sh-# dmesg -n 7
sh-# cat /proc/sys/kernel/printk
7 4 1 7
(2)直接更改printk配置文件，
sh-# echo 1 > /proc/sys/kernel/printk
sh-# cat /proc/sys/kernel/printk
1 4 1 7
2、在写驱动时，需要打印出驱动相关的调试信息：
内核在IIC驱动(
./drivers/i2c/ )的makefile有如下代码:
ifeq ($(CONFIG_I2C_DEBUG_CORE),y)
EXTRA_CFLAGS += -DDEBUG
endif
Kconfig里面当然也有对应的:
config I2C_DEBUG_CORE bool "I2C Core debugging messages"
help Say Y here if you want the I2C core to produce a bunch of debug
messages to the system log. Select this if you are having a
problem with I2C support and want to see more of what is going on.
在配置内核时, 设置IIC对应的debug项目:
Device Drivers --->
<*> I2C support -->
<*> I2C Core debugging messages
<*> I2C Algorithm debugging messages
<*> I2C Bus debugging messages
<*> I2C Chip debugging messages
重新编译内核然. 烧写启动后更该printk的缺省值:#echo 8 > /proc/sys/kernel/printk
后运行 ./i2c_test, 会看见如下的调试信息:
注: IIC测试程序代码:http://blog.csdn.net/hongtao_liu/article/details/4964244
i2c-adapter i2c-0: ioctl, cmd=0x702, arg=0x01
i2c-adapter i2c-0: ioctl, cmd=0x701, arg=0x02
i2c-adapter i2c-0: ioctl, cmd=0x707, arg=0xbeb95d28
i2c-adapter i2c-0: master_xfer[0] W, addr=0x50, len=2
s3c2440-i2c s3c2440-i2c: START: 000000d0 to IICSTAT, a0 to DS
s3c2440-i2c s3c2440-i2c: iiccon, 000000e0
s3c2440-i2c s3c2440-i2c: STOP