diff --git a/common/mousekey.h b/common/mousekey.h
index ac26a46c..d8d7beaa 100644
--- a/common/mousekey.h
+++ b/common/mousekey.h
@@ -45,7 +45,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define MOUSEKEY_TIME_TO_MAX 20
 #endif
 #ifndef MOUSEKEY_WHEEL_MAX_SPEED
-#define MOUSEKEY_WHEEL_MAX_SPEED 16
+#define MOUSEKEY_WHEEL_MAX_SPEED 8
 #endif
 #ifndef MOUSEKEY_WHEEL_TIME_TO_MAX
 #define MOUSEKEY_WHEEL_TIME_TO_MAX 40
diff --git a/protocol/serial.c b/protocol/serial_soft.c
similarity index 71%
rename from protocol/serial.c
rename to protocol/serial_soft.c
index b5c2ae31..b7d06b64 100644
--- a/protocol/serial.c
+++ b/protocol/serial_soft.c
@@ -38,12 +38,19 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <stdbool.h>
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include <util/delay.h>
 #include "serial.h"
 
+/*
+ *  Stupid Inefficient Busy-wait Software Serial
+ *  is still useful for negative logic signal like Sun protocol not supported by hardware USART.
+ */
+
+#define WAIT_US     (1000000/SERIAL_BAUD)
 
 void serial_init(void)
 {
-    SERIAL_RX_INIT();
+    SERIAL_RXD_INIT();
 }
 
 // RX ring buffer
@@ -64,12 +71,44 @@ uint8_t serial_recv(void)
     return data;
 }
 
-// USART RX complete interrupt
-ISR(SERIAL_RX_VECT)
+//ISR(INT2_vect)
+ISR(SERIAL_RXD_VECT)
 {
+    SERIAL_RXD_INT_ENTER()
+
+    uint8_t data = 0;
+#ifdef SERIAL_BIT_ORDER_MSB
+    uint8_t pos = 0x80;
+#else
+    uint8_t pos = 0x01;
+#endif
+    // to center of start bit
+    _delay_us(WAIT_US/2);
+    do {
+        // to center of next bit
+        _delay_us(WAIT_US);
+
+        if (SERIAL_RXD_PIN&(1<<SERIAL_RXD_BIT)) {
+            data |= pos;
+        }
+#ifdef SERIAL_BIT_ORDER_MSB
+        pos >>= 1;
+#else
+        pos <<= 1;
+#endif
+    } while (pos);
+    // to center of stop bit
+    _delay_us(WAIT_US);
+
+#ifdef SERIAL_NEGATIVE_LOGIC
+    data = ~data;
+#endif
+
     uint8_t next = (rbuf_head + 1) % RBUF_SIZE;
     if (next != rbuf_tail) {
-        rbuf[rbuf_head] = SERIAL_RX_DATA;
+        rbuf[rbuf_head] = data;
         rbuf_head = next;
     }
+
+    SERIAL_RXD_INT_EXIT();
 }
diff --git a/rules.mk b/rules.mk
index f53fe912..2e4fce51 100644
--- a/rules.mk
+++ b/rules.mk
@@ -252,7 +252,7 @@ EXTMEMOPTS =
 # 	(.vectors+0x30): relocation truncated to fit: R_AVR_13_PCREL against symbol `__vector_12'
 #
 LDFLAGS = -Wl,-Map=$(TARGET).map,--cref
-LDFLAGS += -Wl,--relax
+#LDFLAGS += -Wl,--relax
 LDFLAGS += -Wl,--gc-sections
 LDFLAGS += $(EXTMEMOPTS)
 LDFLAGS += $(patsubst %,-L%,$(EXTRALIBDIRS))