19 files changed, 514 insertions, 173 deletions

diff --git a/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h b/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
index be2e7cb8b..b991b874b 100644
--- a/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
+++ b/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
@@ -9,7 +9,7 @@
 #define SERIAL_PIN_INTERRUPT INT2_vect
 
 #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-#define SERIAL_MASTER_BUFFER_LENGTH 1
+#define SERIAL_MASTER_BUFFER_LENGTH 0
 
 //// #error rev1/keymaps/OLED_sample serial config
 
diff --git a/keyboards/helix/rev1/rules.mk b/keyboards/helix/rev1/rules.mk
index daba80eae..13834f5da 100644
--- a/keyboards/helix/rev1/rules.mk
+++ b/keyboards/helix/rev1/rules.mk
@@ -1,4 +1,4 @@
-SRC += rev1/matrix.c \
-           rev1/split_util.c
+SRC += rev1/matrix.c
+SRC += rev1/split_util.c
 
 BACKLIGHT_ENABLE = no
diff --git a/keyboards/helix/rev1/serial_config.h b/keyboards/helix/rev1/serial_config.h
index 2b668a6af..51c6aa375 100644
--- a/keyboards/helix/rev1/serial_config.h
+++ b/keyboards/helix/rev1/serial_config.h
@@ -9,7 +9,7 @@
 #define SERIAL_PIN_INTERRUPT INT0_vect
 
 #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-#define SERIAL_MASTER_BUFFER_LENGTH 1
+#define SERIAL_MASTER_BUFFER_LENGTH 0
 
 /// #error rev1 serial config
 
diff --git a/keyboards/helix/rev2/keymaps/default/config.h b/keyboards/helix/rev2/keymaps/default/config.h
index 6da6849a1..185e67838 100644
--- a/keyboards/helix/rev2/keymaps/default/config.h
+++ b/keyboards/helix/rev2/keymaps/default/config.h
@@ -21,6 +21,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef CONFIG_USER_H
 #define CONFIG_USER_H
 
+// if you need more program area, try uncomment follow line
+//#include "serial_config_simpleapi.h"
+
 // place overrides here
 
 #endif /* CONFIG_USER_H */
diff --git a/keyboards/helix/rev2/keymaps/edvorakjp/config.h b/keyboards/helix/rev2/keymaps/edvorakjp/config.h
index a7a5f8360..ead31605b 100644
--- a/keyboards/helix/rev2/keymaps/edvorakjp/config.h
+++ b/keyboards/helix/rev2/keymaps/edvorakjp/config.h
@@ -1,6 +1,9 @@
 #ifndef CONFIG_USER_H
 #define CONFIG_USER_H
 
+// if you need more program area, try uncomment follow line
+//#include "serial_config_simpleapi.h"
+
 #undef TAPPING_FORCE_HOLD
 #undef TAPPING_TERM
 #define TAPPING_TERM 120
diff --git a/keyboards/helix/rev2/keymaps/five_rows/config.h b/keyboards/helix/rev2/keymaps/five_rows/config.h
index 6da6849a1..837219460 100644
--- a/keyboards/helix/rev2/keymaps/five_rows/config.h
+++ b/keyboards/helix/rev2/keymaps/five_rows/config.h
@@ -21,6 +21,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef CONFIG_USER_H
 #define CONFIG_USER_H
 
+// if you need more program area, try uncomment follow line
+//#include "serial_config_simpleapi.h"
+
+#undef TAPPING_TERM
+#define TAPPING_TERM 140
+
 // place overrides here
 
 #endif /* CONFIG_USER_H */
diff --git a/keyboards/helix/rev2/keymaps/five_rows_jis/config.h b/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
index 34650b99a..c380b7db4 100644
--- a/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
+++ b/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
@@ -23,6 +23,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 // place overrides here
 
+// if you need more program area, try uncomment follow line
+//#include "serial_config_simpleapi.h"
+
 #ifdef MOUSEKEY_ENABLE
   #undef MOUSEKEY_INTERVAL
   #define MOUSEKEY_INTERVAL 0
diff --git a/keyboards/helix/rev2/keymaps/froggy/config.h b/keyboards/helix/rev2/keymaps/froggy/config.h
index df72aef12..dad248303 100644
--- a/keyboards/helix/rev2/keymaps/froggy/config.h
+++ b/keyboards/helix/rev2/keymaps/froggy/config.h
@@ -21,6 +21,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef CONFIG_USER_H
 #define CONFIG_USER_H
 
+// if you need more program area, try uncomment follow line
+//#include "serial_config_simpleapi.h"
+
 #undef TAPPING_TERM
 #define TAPPING_TERM 200
 #define ONESHOT_TAP_TOGGLE 5 /* Tapping this number of times holds the key until tapped this number of times again. */
diff --git a/keyboards/helix/rev2/keymaps/led_test/config.h b/keyboards/helix/rev2/keymaps/led_test/config.h
index 6da6849a1..043825452 100644
--- a/keyboards/helix/rev2/keymaps/led_test/config.h
+++ b/keyboards/helix/rev2/keymaps/led_test/config.h
@@ -21,6 +21,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef CONFIG_USER_H
 #define CONFIG_USER_H
 
+// if you need more program area, try uncomment follow line
+#include "serial_config_simpleapi.h"
+
 // place overrides here
 
 #endif /* CONFIG_USER_H */
diff --git a/keyboards/helix/rev2/matrix.c b/keyboards/helix/rev2/matrix.c
index 8a1ce3af1..322959dbb 100644
--- a/keyboards/helix/rev2/matrix.c
+++ b/keyboards/helix/rev2/matrix.c
@@ -20,6 +20,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <stdint.h>
 #include <stdbool.h>
+#include <string.h>
 #include <avr/io.h>
 #include <avr/wdt.h>
 #include <avr/interrupt.h>
@@ -34,7 +35,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifdef USE_MATRIX_I2C
 #  include "i2c.h"
 #else // USE_SERIAL
-#  include "serial.h"
+#  include "split_scomm.h"
 #endif
 
 #ifndef DEBOUNCE
@@ -102,6 +103,8 @@ void matrix_init(void)
     init_cols();
 
     TX_RX_LED_INIT;
+    TXLED0;
+    RXLED0;
 
     // initialize matrix state: all keys off
     for (uint8_t i=0; i < MATRIX_ROWS; i++) {
@@ -178,17 +181,20 @@ i2c_error: // the cable is disconnceted, or something else went wrong
 
 #else // USE_SERIAL
 
-int serial_transaction(void) {
+int serial_transaction(int master_changed) {
     int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+    int ret=serial_update_buffers(master_changed);
+#else
     int ret=serial_update_buffers();
+#endif
     if (ret ) {
-        if(ret==2)RXLED1;
+        if(ret==2) RXLED1;
         return 1;
     }
-RXLED0;
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        matrix[slaveOffset+i] = serial_slave_buffer[i];
-    }
+    RXLED0;
+    memcpy(&matrix[slaveOffset],
+        (void *)serial_slave_buffer, sizeof(serial_slave_buffer));
     return 0;
 }
 #endif
@@ -199,19 +205,9 @@ uint8_t matrix_scan(void)
         matrix_master_scan();
     }else{
         matrix_slave_scan();
-
-//        if(serial_slave_DATA_CORRUPT()){
-//          TXLED0;
-          int offset = (isLeftHand) ? ROWS_PER_HAND : 0;
-
-          for (int i = 0; i < ROWS_PER_HAND; ++i) {
-              matrix[offset+i] = serial_master_buffer[i];
-          }
-
-//        }else{
-//          TXLED1;
-//        }
-
+        int offset = (isLeftHand) ? ROWS_PER_HAND : 0;
+        memcpy(&matrix[offset],
+               (void *)serial_master_buffer, sizeof(serial_master_buffer));
         matrix_scan_quantum();
     }
     return 1;
@@ -221,6 +217,7 @@ uint8_t matrix_scan(void)
 uint8_t matrix_master_scan(void) {
 
     int ret = _matrix_scan();
+    int mchanged = 1;
 
 #ifndef KEYBOARD_helix_rev1
     int offset = (isLeftHand) ? 0 : ROWS_PER_HAND;
@@ -231,16 +228,19 @@ uint8_t matrix_master_scan(void) {
 //        i2c_slave_buffer[i] = matrix[offset+i];
 //    }
 #else // USE_SERIAL
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        serial_master_buffer[i] = matrix[offset+i];
-    }
+  #ifdef SERIAL_USE_MULTI_TRANSACTION
+    mchanged = memcmp((void *)serial_master_buffer,
+                      &matrix[offset], sizeof(serial_master_buffer));
+  #endif
+    memcpy((void *)serial_master_buffer,
+           &matrix[offset], sizeof(serial_master_buffer));
 #endif
 #endif
 
 #ifdef USE_MATRIX_I2C
     if( i2c_transaction() ) {
 #else // USE_SERIAL
-    if( serial_transaction() ) {
+    if( serial_transaction(mchanged) ) {
 #endif
         // turn on the indicator led when halves are disconnected
         TXLED1;
@@ -274,9 +274,19 @@ void matrix_slave_scan(void) {
         i2c_slave_buffer[i] = matrix[offset+i];
     }
 #else // USE_SERIAL
+  #ifdef SERIAL_USE_MULTI_TRANSACTION
+    int change = 0;
+  #endif
     for (int i = 0; i < ROWS_PER_HAND; ++i) {
+  #ifdef SERIAL_USE_MULTI_TRANSACTION
+        if( serial_slave_buffer[i] != matrix[offset+i] )
+            change = 1;
+  #endif
         serial_slave_buffer[i] = matrix[offset+i];
     }
+  #ifdef SERIAL_USE_MULTI_TRANSACTION
+    slave_buffer_change_count += change;
+  #endif
 #endif
 }
 
diff --git a/keyboards/helix/rev2/rules.mk b/keyboards/helix/rev2/rules.mk
index 6ab01f44b..4ea623c43 100644
--- a/keyboards/helix/rev2/rules.mk
+++ b/keyboards/helix/rev2/rules.mk
@@ -1,3 +1,4 @@
-SRC += rev2/matrix.c \
-           rev2/split_util.c \
-           ws2812.c
+SRC += rev2/matrix.c
+SRC += rev2/split_util.c
+SRC += rev2/split_scomm.c
+SRC += ws2812.c
diff --git a/keyboards/helix/rev2/serial_config.h b/keyboards/helix/rev2/serial_config.h
index 82c6e4e83..8d7e62837 100644
--- a/keyboards/helix/rev2/serial_config.h
+++ b/keyboards/helix/rev2/serial_config.h
@@ -8,8 +8,7 @@
 #define SERIAL_PIN_MASK _BV(PD2)
 #define SERIAL_PIN_INTERRUPT INT2_vect
 
-#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-#define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_USE_MULTI_TRANSACTION
 
 //// #error rev2 serial config
 
diff --git a/keyboards/helix/rev2/serial_config_simpleapi.h b/keyboards/helix/rev2/serial_config_simpleapi.h
new file mode 100644
index 000000000..e2d22a41e
--- /dev/null
+++ b/keyboards/helix/rev2/serial_config_simpleapi.h
@@ -0,0 +1,8 @@
+#ifndef SERIAL_CONFIG_SIMPLEAPI_H
+#define SERIAL_CONFIG_SIMPLEAPI_H
+
+#undef SERIAL_USE_MULTI_TRANSACTION
+#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
+
+#endif // SERIAL_CONFIG_SIMPLEAPI_H
diff --git a/keyboards/helix/rev2/split_scomm.c b/keyboards/helix/rev2/split_scomm.c
new file mode 100644
index 000000000..9719eb22e
--- /dev/null
+++ b/keyboards/helix/rev2/split_scomm.c
@@ -0,0 +1,73 @@
+#ifdef USE_SERIAL
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE flexible API (using multi-type transaction function) --- */
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stddef.h>
+#include <split_scomm.h>
+#include "serial.h"
+#ifdef SERIAL_DEBUG_MODE
+#include <avr/io.h>
+#endif
+
+uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
+uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
+uint8_t volatile status_com = 0;
+uint8_t volatile status1 = 0;
+uint8_t slave_buffer_change_count = 0;
+uint8_t s_change_old = 0xff;
+
+SSTD_t transactions[] = {
+#define GET_SLAVE_STATUS 0
+    /* master buffer not changed, only recive slave_buffer_change_count */
+    { (uint8_t *)&status_com,
+      0, NULL,
+      sizeof(slave_buffer_change_count), &slave_buffer_change_count,
+    },
+#define PUT_MASTER_GET_SLAVE_STATUS 1
+    /* master buffer changed need send, and recive slave_buffer_change_count  */
+    { (uint8_t *)&status_com,
+      sizeof(serial_master_buffer), (uint8_t *)serial_master_buffer,
+      sizeof(slave_buffer_change_count), &slave_buffer_change_count,
+    },
+#define GET_SLAVE_BUFFER 2
+    /* recive serial_slave_buffer */
+    { (uint8_t *)&status1,
+      0, NULL,
+      sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
+    }
+};
+
+void serial_master_init(void)
+{
+    soft_serial_initiator_init(transactions);
+}
+
+void serial_slave_init(void)
+{
+    soft_serial_target_init(transactions);
+}
+
+// 0 => no error
+// 1 => slave did not respond
+// 2 => checksum error
+int serial_update_buffers(int master_update)
+{
+    int status;
+    static int need_retry = 0;
+    if( s_change_old != slave_buffer_change_count ) {
+        status = soft_serial_transaction(GET_SLAVE_BUFFER);
+        if( status == TRANSACTION_END )
+            s_change_old = slave_buffer_change_count;
+    }
+    if( !master_update && !need_retry)
+        status = soft_serial_transaction(GET_SLAVE_STATUS);
+    else
+        status = soft_serial_transaction(PUT_MASTER_GET_SLAVE_STATUS);
+    need_retry = ( status == TRANSACTION_END ) ? 0 : 1;
+    return status;
+}
+
+#endif // SERIAL_USE_MULTI_TRANSACTION
+#endif /* USE_SERIAL */
diff --git a/keyboards/helix/rev2/split_scomm.h b/keyboards/helix/rev2/split_scomm.h
new file mode 100644
index 000000000..873d8939d
--- /dev/null
+++ b/keyboards/helix/rev2/split_scomm.h
@@ -0,0 +1,24 @@
+#ifndef SPLIT_COMM_H
+#define SPLIT_COMM_H
+
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) --- */
+#include "serial.h"
+
+#else
+/* --- USE flexible API (using multi-type transaction function) --- */
+// Buffers for master - slave communication
+#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
+
+extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
+extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
+extern uint8_t slave_buffer_change_count;
+
+void serial_master_init(void);
+void serial_slave_init(void);
+int serial_update_buffers(int master_changed);
+
+#endif
+
+#endif /* SPLIT_COMM_H */
diff --git a/keyboards/helix/rev2/split_util.c b/keyboards/helix/rev2/split_util.c
index beb39fa00..e1ff8b437 100644
--- a/keyboards/helix/rev2/split_util.c
+++ b/keyboards/helix/rev2/split_util.c
@@ -11,7 +11,7 @@
 #ifdef USE_MATRIX_I2C
 #  include "i2c.h"
 #else
-#  include "serial.h"
+#  include "split_scomm.h"
 #endif
 
 volatile bool isLeftHand = true;
diff --git a/keyboards/helix/rules.mk b/keyboards/helix/rules.mk
index c35f93fb0..e42f92cf8 100644
--- a/keyboards/helix/rules.mk
+++ b/keyboards/helix/rules.mk
@@ -1,6 +1,9 @@
-SRC += i2c.c \
-           serial.c \
-           ssd1306.c
+SRC += i2c.c
+SRC += serial.c
+SRC += ssd1306.c
+
+# if firmware size over limit, try this option
+# CFLAGS += -flto
 
 # MCU name
 #MCU = at90usb1287
diff --git a/keyboards/helix/serial.c b/keyboards/helix/serial.c
index 591941587..11ceff0b3 100644
--- a/keyboards/helix/serial.c
+++ b/keyboards/helix/serial.c
@@ -9,40 +9,85 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
+#include <stddef.h>
 #include <stdbool.h>
 #include "serial.h"
+//#include <pro_micro.h>
 
 #ifdef USE_SERIAL
 
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) */
+  #if SERIAL_SLAVE_BUFFER_LENGTH > 0
+  uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
+  #endif
+  #if SERIAL_MASTER_BUFFER_LENGTH > 0
+  uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
+  #endif
+  uint8_t volatile status0 = 0;
+
+SSTD_t transactions[] = {
+    { (uint8_t *)&status0,
+  #if SERIAL_MASTER_BUFFER_LENGTH > 0
+      sizeof(serial_master_buffer), (uint8_t *)serial_master_buffer,
+  #else
+      0, (uint8_t *)NULL,
+  #endif
+  #if SERIAL_SLAVE_BUFFER_LENGTH > 0
+      sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
+  #else
+      0, (uint8_t *)NULL,
+  #endif
+  }
+};
+
+void serial_master_init(void)
+{ soft_serial_initiator_init(transactions); }
+
+void serial_slave_init(void)
+{ soft_serial_target_init(transactions); }
+
+// 0 => no error
+// 1 => slave did not respond
+// 2 => checksum error
+int serial_update_buffers()
+{ return soft_serial_transaction(); }
+
+#endif // Simple API (OLD API, compatible with let's split serial.c)
+
+#define ALWAYS_INLINE __attribute__((always_inline))
+#define NO_INLINE __attribute__((noinline))
 #define _delay_sub_us(x)    __builtin_avr_delay_cycles(x)
 
 // Serial pulse period in microseconds.
+#define TID_SEND_ADJUST 14
+
 #define SELECT_SERIAL_SPEED 1
 #if SELECT_SERIAL_SPEED == 0
   // Very High speed
   #define SERIAL_DELAY 4             // micro sec
-  #define READ_WRITE_START_ADJUST 30 // cycles
-  #define READ_WRITE_WIDTH_ADJUST 10 // cycles
+  #define READ_WRITE_START_ADJUST 33 // cycles
+  #define READ_WRITE_WIDTH_ADJUST 3 // cycles
 #elif SELECT_SERIAL_SPEED == 1
   // High speed
   #define SERIAL_DELAY 6             // micro sec
-  #define READ_WRITE_START_ADJUST 23 // cycles
-  #define READ_WRITE_WIDTH_ADJUST 10 // cycles
+  #define READ_WRITE_START_ADJUST 30 // cycles
+  #define READ_WRITE_WIDTH_ADJUST 3 // cycles
 #elif SELECT_SERIAL_SPEED == 2
   // Middle speed
   #define SERIAL_DELAY 12            // micro sec
-  #define READ_WRITE_START_ADJUST 25 // cycles
-  #define READ_WRITE_WIDTH_ADJUST 10 // cycles
+  #define READ_WRITE_START_ADJUST 30 // cycles
+  #define READ_WRITE_WIDTH_ADJUST 3 // cycles
 #elif SELECT_SERIAL_SPEED == 3
   // Low speed
   #define SERIAL_DELAY 24            // micro sec
-  #define READ_WRITE_START_ADJUST 25 // cycles
-  #define READ_WRITE_WIDTH_ADJUST 10 // cycles
+  #define READ_WRITE_START_ADJUST 30 // cycles
+  #define READ_WRITE_WIDTH_ADJUST 3 // cycles
 #elif SELECT_SERIAL_SPEED == 4
   // Very Low speed
   #define SERIAL_DELAY 50            // micro sec
-  #define READ_WRITE_START_ADJUST 25 // cycles
-  #define READ_WRITE_WIDTH_ADJUST 10 // cycles
+  #define READ_WRITE_START_ADJUST 30 // cycles
+  #define READ_WRITE_WIDTH_ADJUST 3 // cycles
 #else
 #error Illegal Serial Speed
 #endif
@@ -51,14 +96,15 @@
 #define SERIAL_DELAY_HALF1 (SERIAL_DELAY/2)
 #define SERIAL_DELAY_HALF2 (SERIAL_DELAY - SERIAL_DELAY/2)
 
-#define SLAVE_INT_WIDTH 1
-#define SLAVE_INT_RESPONSE_TIME SERIAL_DELAY
-
-uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
-uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
+#define SLAVE_INT_WIDTH_US 1
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+  #define SLAVE_INT_RESPONSE_TIME SERIAL_DELAY
+#else
+  #define SLAVE_INT_ACK_WIDTH_UNIT 2
+  #define SLAVE_INT_ACK_WIDTH 4
+#endif
 
-#define SLAVE_DATA_CORRUPT (1<<0)
-volatile uint8_t status = 0;
+static SSTD_t *Transaction_table = NULL;
 
 inline static
 void serial_delay(void) {
@@ -75,12 +121,14 @@ void serial_delay_half2(void) {
   _delay_us(SERIAL_DELAY_HALF2);
 }
 
+inline static void serial_output(void) ALWAYS_INLINE;
 inline static
 void serial_output(void) {
   SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
 }
 
 // make the serial pin an input with pull-up resistor
+inline static void serial_input_with_pullup(void) ALWAYS_INLINE;
 inline static
 void serial_input_with_pullup(void) {
   SERIAL_PIN_DDR  &= ~SERIAL_PIN_MASK;
@@ -92,50 +140,58 @@ uint8_t serial_read_pin(void) {
   return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
 }
 
+inline static void serial_low(void) ALWAYS_INLINE;
 inline static
 void serial_low(void) {
   SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
 }
 
+inline static void serial_high(void) ALWAYS_INLINE;
 inline static
 void serial_high(void) {
   SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
 }
 
-void serial_master_init(void) {
-  serial_output();
-  serial_high();
+void soft_serial_initiator_init(SSTD_t *sstd_table)
+{
+    Transaction_table = sstd_table;
+    serial_output();
+    serial_high();
 }
 
-void serial_slave_init(void) {
-  serial_input_with_pullup();
+void soft_serial_target_init(SSTD_t *sstd_table)
+{
+    Transaction_table = sstd_table;
+    serial_input_with_pullup();
 
 #if SERIAL_PIN_MASK == _BV(PD0)
-  // Enable INT0
-  EIMSK |= _BV(INT0);
-  // Trigger on falling edge of INT0
-  EICRA &= ~(_BV(ISC00) | _BV(ISC01));
+    // Enable INT0
+    EIMSK |= _BV(INT0);
+    // Trigger on falling edge of INT0
+    EICRA &= ~(_BV(ISC00) | _BV(ISC01));
 #elif SERIAL_PIN_MASK == _BV(PD2)
-  // Enable INT2
-  EIMSK |= _BV(INT2);
-  // Trigger on falling edge of INT2
-  EICRA &= ~(_BV(ISC20) | _BV(ISC21));
+    // Enable INT2
+    EIMSK |= _BV(INT2);
+    // Trigger on falling edge of INT2
+    EICRA &= ~(_BV(ISC20) | _BV(ISC21));
 #else
  #error unknown SERIAL_PIN_MASK value
 #endif
 }
 
 // Used by the sender to synchronize timing with the reciver.
+static void sync_recv(void) NO_INLINE;
 static
 void sync_recv(void) {
-  for (int i = 0; i < SERIAL_DELAY*5 && serial_read_pin(); i++ ) {
+  for (uint8_t i = 0; i < SERIAL_DELAY*5 && serial_read_pin(); i++ ) {
   }
-  // This shouldn't hang if the slave disconnects because the
-  // serial line will float to high if the slave does disconnect.
+  // This shouldn't hang if the target disconnects because the
+  // serial line will float to high if the target does disconnect.
   while (!serial_read_pin());
 }
 
 // Used by the reciver to send a synchronization signal to the sender.
+static void sync_send(void)NO_INLINE;
 static
 void sync_send(void) {
   serial_low();
@@ -144,152 +200,245 @@ void sync_send(void) {
 }
 
 // Reads a byte from the serial line
-static
-uint8_t serial_read_byte(void) {
-  uint8_t byte = 0;
+static uint8_t serial_read_chunk(uint8_t *pterrcount, uint8_t bit) NO_INLINE;
+static uint8_t serial_read_chunk(uint8_t *pterrcount, uint8_t bit) {
+    uint8_t byte, i, p, pb;
+
   _delay_sub_us(READ_WRITE_START_ADJUST);
-  for ( uint8_t i = 0; i < 8; ++i) {
-    serial_delay_half1();   // read the middle of pulses
-    byte = (byte << 1) | serial_read_pin();
-    _delay_sub_us(READ_WRITE_WIDTH_ADJUST);
-    serial_delay_half2();
+  for( i = 0, byte = 0, p = 0; i < bit; i++ ) {
+      serial_delay_half1();   // read the middle of pulses
+      if( serial_read_pin() ) {
+          byte = (byte << 1) | 1; p ^= 1;
+      } else {
+          byte = (byte << 1) | 0; p ^= 0;
+      }
+      _delay_sub_us(READ_WRITE_WIDTH_ADJUST);
+      serial_delay_half2();
   }
+  /* recive parity bit */
+  serial_delay_half1();   // read the middle of pulses
+  pb = serial_read_pin();
+  _delay_sub_us(READ_WRITE_WIDTH_ADJUST);
+  serial_delay_half2();
+
+  *pterrcount += (p != pb)? 1 : 0;
+
   return byte;
 }
 
 // Sends a byte with MSB ordering
-static
-void serial_write_byte(uint8_t data) {
-  uint8_t b = 1<<7;
-  while( b ) {
-    if(data & b) {
-      serial_high();
-    } else {
-      serial_low();
+void serial_write_chunk(uint8_t data, uint8_t bit) NO_INLINE;
+void serial_write_chunk(uint8_t data, uint8_t bit) {
+    uint8_t b, p;
+    for( p = 0, b = 1<<(bit-1); b ; b >>= 1) {
+        if(data & b) {
+            serial_high(); p ^= 1;
+        } else {
+            serial_low();  p ^= 0;
+        }
+        serial_delay();
     }
-    b >>= 1;
+    /* send parity bit */
+    if(p & 1) { serial_high(); }
+    else      { serial_low(); }
     serial_delay();
-  }
-  serial_low(); // sync_send() / senc_recv() need raise edge
-}
 
-// interrupt handle to be used by the slave device
-ISR(SERIAL_PIN_INTERRUPT) {
-  serial_output();
+    serial_low(); // sync_send() / senc_recv() need raise edge
+}
 
-  // slave send phase
-  uint8_t checksum = 0;
-  for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
+static void serial_send_packet(uint8_t *buffer, uint8_t size) NO_INLINE;
+static
+void serial_send_packet(uint8_t *buffer, uint8_t size) {
+  for (uint8_t i = 0; i < size; ++i) {
+    uint8_t data;
+    data = buffer[i];
     sync_send();
-    serial_write_byte(serial_slave_buffer[i]);
-    checksum += serial_slave_buffer[i];
+    serial_write_chunk(data,8);
   }
-  sync_send();
-  serial_write_byte(checksum);
-
-  // slave switch to input
-  sync_send(); //0
-  serial_delay_half1(); //1
-  serial_low();         //2
-  serial_input_with_pullup(); //2
-  serial_delay_half1(); //3
-
-  // slave recive phase
-  uint8_t checksum_computed = 0;
-  for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
+}
+
+static uint8_t serial_recive_packet(uint8_t *buffer, uint8_t size) NO_INLINE;
+static
+uint8_t serial_recive_packet(uint8_t *buffer, uint8_t size) {
+  uint8_t pecount = 0;
+  for (uint8_t i = 0; i < size; ++i) {
+    uint8_t data;
     sync_recv();
-    serial_master_buffer[i] = serial_read_byte();
-    checksum_computed += serial_master_buffer[i];
+    data = serial_read_chunk(&pecount, 8);
+    buffer[i] = data;
   }
+  return pecount == 0;
+}
+
+inline static
+void change_sender2reciver(void) {
+    sync_send();          //0
+    serial_delay_half1(); //1
+    serial_low();         //2
+    serial_input_with_pullup(); //2
+    serial_delay_half1(); //3
+}
+
+inline static
+void change_reciver2sender(void) {
+    sync_recv();     //0
+    serial_delay();  //1
+    serial_low();    //3
+    serial_output(); //3
+    serial_delay_half1(); //4
+}
+
+// interrupt handle to be used by the target device
+ISR(SERIAL_PIN_INTERRUPT) {
+
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+  serial_low();
+  serial_output();
+  SSTD_t *trans = Transaction_table;
+#else
+  // recive transaction table index
+  uint8_t tid;
+  uint8_t pecount = 0;
   sync_recv();
-  uint8_t checksum_received = serial_read_byte();
+  tid = serial_read_chunk(&pecount,4);
+  if(pecount> 0)
+      return;
+  serial_delay_half1();
 
-  if ( checksum_computed != checksum_received ) {
-    status |= SLAVE_DATA_CORRUPT;
+  serial_high(); // response step1 low->high
+  serial_output();
+  _delay_sub_us(SLAVE_INT_ACK_WIDTH_UNIT*SLAVE_INT_ACK_WIDTH);
+  SSTD_t *trans = &Transaction_table[tid];
+  serial_low(); // response step2 ack high->low
+#endif
+
+  // target send phase
+  if( trans->target2initiator_buffer_size > 0 )
+      serial_send_packet((uint8_t *)trans->target2initiator_buffer,
+                         trans->target2initiator_buffer_size);
+  // target switch to input
+  change_sender2reciver();
+
+  // target recive phase
+  if( trans->initiator2target_buffer_size > 0 ) {
+      if (serial_recive_packet((uint8_t *)trans->initiator2target_buffer,
+                               trans->initiator2target_buffer_size) ) {
+          *trans->status = TRANSACTION_ACCEPTED;
+      } else {
+          *trans->status = TRANSACTION_DATA_ERROR;
+      }
   } else {
-    status &= ~SLAVE_DATA_CORRUPT;
+      *trans->status = TRANSACTION_ACCEPTED;
   }
 
-  sync_recv(); //weit master output to high
-}
-
-inline
-bool serial_slave_DATA_CORRUPT(void) {
-  return status & SLAVE_DATA_CORRUPT;
+  sync_recv(); //weit initiator output to high
 }
 
-// Copies the serial_slave_buffer to the master and sends the
-// serial_master_buffer to the slave.
+/////////
+//  start transaction by initiator
+//
+// int  soft_serial_transaction(int sstd_index)
 //
 // Returns:
-// 0 => no error
-// 1 => slave did not respond
-// 2 => checksum error
-int serial_update_buffers(void) {
-  // this code is very time dependent, so we need to disable interrupts
+//    TRANSACTION_END
+//    TRANSACTION_NO_RESPONSE
+//    TRANSACTION_DATA_ERROR
+// this code is very time dependent, so we need to disable interrupts
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+int  soft_serial_transaction(void) {
+  SSTD_t *trans = Transaction_table;
+#else
+int  soft_serial_transaction(int sstd_index) {
+  SSTD_t *trans = &Transaction_table[sstd_index];
+#endif
   cli();
 
-  // signal to the slave that we want to start a transaction
+  // signal to the target that we want to start a transaction
   serial_output();
   serial_low();
-  _delay_us(SLAVE_INT_WIDTH);
+  _delay_us(SLAVE_INT_WIDTH_US);
 
-  // wait for the slaves response
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+  // wait for the target response
   serial_input_with_pullup();
   _delay_us(SLAVE_INT_RESPONSE_TIME);
 
-  // check if the slave is present
+  // check if the target is present
   if (serial_read_pin()) {
-    // slave failed to pull the line low, assume not present
+    // target failed to pull the line low, assume not present
     serial_output();
     serial_high();
+    *trans->status = TRANSACTION_NO_RESPONSE;
     sei();
-    return 1;
+    return TRANSACTION_NO_RESPONSE;
   }
 
-  // master recive phase
-  // if the slave is present syncronize with it
+#else
+  // send transaction table index
+  sync_send();
+  _delay_sub_us(TID_SEND_ADJUST);
+  serial_write_chunk(sstd_index, 4);
+  serial_delay_half1();
 
-  uint8_t checksum_computed = 0;
-  // receive data from the slave
-  for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
-    sync_recv();
-    serial_slave_buffer[i] = serial_read_byte();
-    checksum_computed += serial_slave_buffer[i];
+  // wait for the target response (step1 low->high)
+  serial_input_with_pullup();
+  while( !serial_read_pin() ) {
+      _delay_sub_us(2);
   }
-  sync_recv();
-  uint8_t checksum_received = serial_read_byte();
 
-  if (checksum_computed != checksum_received) {
-    serial_output();
-    serial_high();
-    sei();
-    return 2;
+  // check if the target is present (step2 high->low)
+  for( int i = 0; serial_read_pin(); i++ ) {
+      if (i > SLAVE_INT_ACK_WIDTH + 1) {
+          // slave failed to pull the line low, assume not present
+          serial_output();
+          serial_high();
+          *trans->status = TRANSACTION_NO_RESPONSE;
+          sei();
+          return TRANSACTION_NO_RESPONSE;
+      }
+      _delay_sub_us(SLAVE_INT_ACK_WIDTH_UNIT);
   }
+#endif
 
-  // master switch to output
-  sync_recv(); //0
-  serial_delay();  //1
-  serial_low();    //3
-  serial_output(); // 3
-  serial_delay_half1(); //4
-
-  // master send phase
-  uint8_t checksum = 0;
-
-  for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
-    sync_send();
-    serial_write_byte(serial_master_buffer[i]);
-    checksum += serial_master_buffer[i];
+  // initiator recive phase
+  // if the target is present syncronize with it
+  if( trans->target2initiator_buffer_size > 0 ) {
+      if (!serial_recive_packet((uint8_t *)trans->target2initiator_buffer,
+                                trans->target2initiator_buffer_size) ) {
+          serial_output();
+          serial_high();
+          *trans->status = TRANSACTION_DATA_ERROR;
+          sei();
+          return TRANSACTION_DATA_ERROR;
+      }
+   }
+
+  // initiator switch to output
+  change_reciver2sender();
+
+  // initiator send phase
+  if( trans->initiator2target_buffer_size > 0 ) {
+      serial_send_packet((uint8_t *)trans->initiator2target_buffer,
+                         trans->initiator2target_buffer_size);
   }
-  sync_send();
-  serial_write_byte(checksum);
 
   // always, release the line when not in use
   sync_send();
 
+  *trans->status = TRANSACTION_END;
   sei();
-  return 0;
+  return TRANSACTION_END;
 }
 
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+int soft_serial_get_and_clean_status(int sstd_index) {
+    SSTD_t *trans = &Transaction_table[sstd_index];
+    cli();
+    int retval = *trans->status;
+    *trans->status = 0;;
+    sei();
+    return retval;
+}
+#endif
+
 #endif
diff --git a/keyboards/helix/serial.h b/keyboards/helix/serial.h
index c3c9569b2..d2b7fd8e6 100644
--- a/keyboards/helix/serial.h
+++ b/keyboards/helix/serial.h
@@ -3,25 +3,78 @@
 
 #include <stdbool.h>
 
-// ////////////////////////////////////////////
+// /////////////////////////////////////////////////////////////////
 // Need Soft Serial defines in serial_config.h
-// ////////////////////////////////////////////
+// /////////////////////////////////////////////////////////////////
 // ex.
 //  #define SERIAL_PIN_DDR DDRD
 //  #define SERIAL_PIN_PORT PORTD
 //  #define SERIAL_PIN_INPUT PIND
 //  #define SERIAL_PIN_MASK _BV(PD?)   ?=0,2
 //  #define SERIAL_PIN_INTERRUPT INT?_vect  ?=0,2
+//
+// //// USE Simple API (OLD API, compatible with let's split serial.c)
+// ex.
 //  #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-//  #define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
+//  #define SERIAL_MASTER_BUFFER_LENGTH 1
+//
+// //// USE flexible API (using multi-type transaction function)
+//  #define SERIAL_USE_MULTI_TRANSACTION
+//
+// /////////////////////////////////////////////////////////////////
+
 
-// Buffers for master - slave communication
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) */
+#if SERIAL_SLAVE_BUFFER_LENGTH > 0
 extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
+#endif
+#if SERIAL_MASTER_BUFFER_LENGTH > 0
 extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
+#endif
 
 void serial_master_init(void);
 void serial_slave_init(void);
 int serial_update_buffers(void);
-bool serial_slave_data_corrupt(void);
+
+#endif // USE Simple API
+
+// Soft Serial Transaction Descriptor
+typedef struct _SSTD_t  {
+    uint8_t *status;
+    uint8_t initiator2target_buffer_size;
+    uint8_t *initiator2target_buffer;
+    uint8_t target2initiator_buffer_size;
+    uint8_t *target2initiator_buffer;
+} SSTD_t;
+
+// initiator is transaction start side
+void soft_serial_initiator_init(SSTD_t *sstd_table);
+// target is interrupt accept side
+void soft_serial_target_init(SSTD_t *sstd_table);
+
+// initiator resullt
+#define TRANSACTION_END 0
+#define TRANSACTION_NO_RESPONSE 0x1
+#define TRANSACTION_DATA_ERROR  0x2
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+int  soft_serial_transaction(void);
+#else
+int  soft_serial_transaction(int sstd_index);
+#endif
+
+// target status
+// *SSTD_t.status has
+//   initiator:
+//       TRANSACTION_END
+//    or TRANSACTION_NO_RESPONSE
+//    or TRANSACTION_DATA_ERROR
+//   target:
+//       TRANSACTION_DATA_ERROR
+//    or TRANSACTION_ACCEPTED
+#define TRANSACTION_ACCEPTED 0x4
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+int  soft_serial_get_and_clean_status(int sstd_index);
+#endif
 
 #endif /* SOFT_SERIAL_H */