diff --git a/driver/counter.c b/driver/counter.c
index 68b6b4f..e192cbd 100644
--- a/driver/counter.c
+++ b/driver/counter.c
@@ -8,6 +8,7 @@
 #include <linux/spi/spi.h>
 #include <linux/interrupt.h>
 #include <linux/of_irq.h>
+#include <linux/workqueue.h>
 
 #include "ls7366r.h"
 
@@ -109,7 +110,6 @@ static int read32(struct spi_device *client, u8 c, u32 *r) {
     printk("counter - Error! spi_sync_transfer failed in read32\n");
     return ret;
   }
-  printk("counter - Info! rx_buf: %02x %02x %02x %02x %02x\n", rx_buf[0], rx_buf[1], rx_buf[2], rx_buf[3], rx_buf[4]);
   *r = ((u32)rx_buf[1] << 24) | ((u32)rx_buf[2] << 16) | ((u32)rx_buf[3] << 8) | ((u32)rx_buf[4]);
   return 0;
 }
@@ -128,14 +128,11 @@ static int read8(struct spi_device *client, u8 c, u8 *r) {
     printk("counter - Error! spi_sync_transfer failed in read8\n");
     return ret;
   }
-  printk("counter - Info! rx_buf: %02x %02x\n", rx_buf[0], rx_buf[1]);
   *r = rx_buf[1];
   return 0;
 }
 
 
-
-
 static struct of_device_id ls7366r_driver_ids[] = {
   {
     .compatible = "hottis,ls7366r",
@@ -159,6 +156,8 @@ static struct spi_driver ls7366r_driver = {
   },
 };
 
+static struct spi_device *spi_client;
+
 static int dt_ls7366r_probe(struct spi_device *client) {
   printk("counter - ls7366r probing\n");
   
@@ -190,16 +189,12 @@ static int dt_ls7366r_probe(struct spi_device *client) {
     printk("counter - Error! read8 failed in probe\n");
     return ret;
   }
-  printk("counter - Info! x = %02x\n", x);
-
-  u32 y;
-  ret = read32(client, CMD_RD | REG_OTR, &y);
-  if (ret < 0) {
-    printk("counter - Error! read32 failed in probe\n");
-    return ret;
+  if (x != MDR0_ILO) {
+    printk("counter - Error! failed to initialize counter\n");
+    return -1;
   }
-  printk("counter - Info! y = %d\n", y);
 
+  spi_client = client;
 
   return 0;
 }
@@ -233,9 +228,41 @@ static struct platform_driver interrupt_driver = {
 static struct gpio_desc *counter_interrupt;
 static int irq_number;
 
+// workqueue
+struct counter_irq_data {
+  struct work_struct work;
+  u64 timestamp;
+  struct spi_device *client;
+  u64 last_timestamp;
+  u32 last_value;
+};
+static struct counter_irq_data counter_irq_wq_data;
+
+static void counter_worker(struct work_struct *work) {
+  struct counter_irq_data *data = container_of(work, struct counter_irq_data, work);
+  u64 ts = data->timestamp;
+
+  u32 counter_value;
+  int ret = read32(data->client, CMD_RD | REG_OTR, &counter_value);
+
+  if (ret < 0) {
+    printk("counter - Error! read32 failed in counter_worker\n");
+    return;
+  }
+
+  if (data->last_value) {
+    u32 period = counter_value - data->last_value;
+    u64 duration = ts - data->last_timestamp;
+    printk("counter - Info! ts = %llu, duration = %llu, period = %u\n", ts, duration, period);
+  }
+  data->last_value = counter_value;
+  data->last_timestamp = ts;
+}
+
 // ISR
 static irqreturn_t counter_isr(int irq, void *dev_id) {
-  printk("counter - interrupt received\n");
+  counter_irq_wq_data.timestamp = ktime_get();
+  schedule_work(&counter_irq_wq_data.work);
   return IRQ_HANDLED;
 }
 
@@ -244,6 +271,11 @@ static int dt_interrupt_probe(struct platform_device *pdev) {
 
   printk("counter - interrupt probing\n");
 
+  INIT_WORK(&counter_irq_wq_data.work, counter_worker);
+  counter_irq_wq_data.client = spi_client;
+  counter_irq_wq_data.last_value = 0;
+  counter_irq_wq_data.last_timestamp = 0;
+
   counter_interrupt = gpiod_get(dev, "intr", GPIOD_IN);
   if (IS_ERR(counter_interrupt)) {
     printk("counter - Error! Could not setup the GPIO intr\n");