Timer : Periodic

Topics in this section,

• Version Info

• Learnings in this section

• Complete program : timer.c

• Makefile

• Compile Program

• Load the module

• Check if the module is loaded successfully

• Check what happened on module load

• Unload the module

• Check if the module is unloaded successfully

• Check what happened on module unload

Version Info

#	Version
Freebsd	14.1.0

Learnings in this section

• In this program, you are going to learn

• How to create the kernel timer ?

timer.c

#include<sys/param.h>
#include<sys/module.h>
#include<sys/kernel.h>
#include<sys/systm.h>
#include<sys/types.h>
#include<sys/time.h>
#include<sys/malloc.h>

 //  Structure to hold timer data
static struct callout timer_callout;
static int counter = 0;

static void timer_handler(void *arg)
{
	counter++;
	printf("Counter value = %d\n",counter);
	callout_reset(&timer_callout, 5 * hz, timer_handler, NULL);
}

static int event_handler(struct module *module, int event, void *arg)
{

        int  e=0;

        switch(event)
        {
        case MOD_LOAD:
		printf("Module loaded\n");
		
		// Initialize the callout structure
		callout_init(&timer_callout, 1);

		// Schedule the first callout (5 sec)
		callout_reset(&timer_callout, 5 * hz, timer_handler, NULL);
                break;

        case MOD_UNLOAD:
		printf("Module unloaded\n");
		
		// Stop the timer
		callout_stop(&timer_callout);
        	break;

        default:
                e = EOPNOTSUPP;
                break;
	}

return(e);
}

static moduledata_t timer_data = {
	"timer_module",
	event_handler, 
	NULL
};


DECLARE_MODULE(timer_module, timer_data, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);

Makefile

SRCS=timer.c
KMOD=timer_module

.include <bsd.kmod.mk>

Compile Program

$ pwd
basic_device_drivers/timer_periodic


$ ls
timer.c  Makefile


$ make


$ ls
.depend.timer.o           export_syms             machine                 timer.c               timer_module.ko
Makefile                  i386                    opt_global.h            timer.o               x86

Load the module

• Load the module using kldload

$ kldload -v ./timer_module.ko
Loaded ./timer_module.ko, id=8

Check if the module is loaded successfully

• Run kldstat command to check the loaded modules

$ kldstat
Id Refs Address                Size Name
 1   29 0xffffffff80200000  1f6c698 kernel
 2    1 0xffffffff8216d000   772c70 zfs.ko
 3    1 0xffffffff828e1000     7850 cryptodev.ko
 4    1 0xffffffff83218000     3220 intpm.ko
 5    1 0xffffffff8321c000     2178 smbus.ko
 6    1 0xffffffff8321f000     3360 uhid.ko
 7    1 0xffffffff83223000     3360 wmt.ko
 8    1 0xffffffff83227000     20d4 timer_module.ko

Check what happened on module load

• Run dmesg command to check the kernel logs

$ dmesg
Module loaded
Counter value = 1
Counter value = 2
Counter value = 3
Counter value = 4

Unload the module

• Unload the module using kldunload

$ kldunload -v ./timer_module.ko
Unloading timer_module.ko, id=8

Check if the module is unloaded successfully

• Run kldstat command to check the loaded modules

$ kldstat
Id Refs Address                Size Name
 1   27 0xffffffff80200000  1f6c698 kernel
 2    1 0xffffffff8216d000   772c70 zfs.ko
 3    1 0xffffffff828e1000     7850 cryptodev.ko
 4    1 0xffffffff83218000     3220 intpm.ko
 5    1 0xffffffff8321c000     2178 smbus.ko
 6    1 0xffffffff8321f000     3360 uhid.ko
 7    1 0xffffffff83223000     3360 wmt.ko

Check what happened on module unload

• Run dmesg command to check the kernel logs

$ dmesg
Module loaded
Counter value = 1
Counter value = 2
Counter value = 3
Counter value = 4
Counter value = 5
Counter value = 6
Module unloaded