diff --git a/rtl837x_common.h b/rtl837x_common.h
index 7933687..2bb15b4 100644
--- a/rtl837x_common.h
+++ b/rtl837x_common.h
@@ -148,7 +148,7 @@ uint16_t strcpy(register __xdata uint8_t *dst, register const char *s);
 void tcpip_output(void);
 uint8_t read_flash(uint8_t bank, __code uint8_t *addr);
 void get_random_32(void);
-void read_reg_timer(uint32_t * tmr);
+void read_reg_timer(__xdata uint32_t * tmr);
 void sfp_print_info(uint8_t sfp);
 bool gpio_pin_test(uint8_t pin);
 void set_sys_led_state(uint8_t state);
diff --git a/rtlplayground.c b/rtlplayground.c
index 2da920e..2d90077 100644
--- a/rtlplayground.c
+++ b/rtlplayground.c
@@ -688,7 +688,7 @@ void cpy_4(__xdata uint8_t dest[], __xdata uint8_t source[])
 }
 
 
-void read_reg_timer(uint32_t * tmr)
+void read_reg_timer(__xdata uint32_t * tmr)
 {
 	uint8_t * val = (uint8_t *)tmr;
 	SFR_REG_ADDR_U16 = RTL837X_REG_SEC_COUNTER;