Add wired split support using UART communication

app/CMakeLists.txt

@@ -45,7 +45,7 @@ target_sources_ifdef(CONFIG_ZMK_BLE app PRIVATE src/events/battery_state_changed
 target_sources_ifdef(CONFIG_USB app PRIVATE src/events/usb_conn_state_changed.c)
 target_sources(app PRIVATE src/behaviors/behavior_reset.c)
 target_sources_ifdef(CONFIG_ZMK_EXT_POWER app PRIVATE src/behaviors/behavior_ext_power.c)
-if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_BLE_ROLE_CENTRAL)
+if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_BLE_ROLE_CENTRAL OR CONFIG_ZMK_SPLIT_SERIAL_ROLE_CENTRAL)
   target_sources(app PRIVATE src/behaviors/behavior_key_press.c)
   target_sources(app PRIVATE src/behaviors/behavior_hold_tap.c)
   target_sources(app PRIVATE src/behaviors/behavior_sticky_key.c)
@@ -74,6 +74,13 @@ endif()
 if (CONFIG_ZMK_SPLIT_BLE AND CONFIG_ZMK_SPLIT_BLE_ROLE_CENTRAL)
 	target_sources(app PRIVATE src/split/bluetooth/central.c)
 endif()
+if (CONFIG_ZMK_SPLIT_SERIAL AND (NOT CONFIG_ZMK_SPLIT_SERIAL_ROLE_CENTRAL))
+	target_sources(app PRIVATE src/split_listener.c)
+	target_sources(app PRIVATE src/split/serial/service.c)
+endif()
+if (CONFIG_ZMK_SPLIT_SERIAL AND CONFIG_ZMK_SPLIT_SERIAL_ROLE_CENTRAL)
+	target_sources(app PRIVATE src/split/serial/central.c)
+endif()
 target_sources_ifdef(CONFIG_USB app PRIVATE src/usb.c)
 target_sources_ifdef(CONFIG_ZMK_BLE app PRIVATE src/hog.c)
 target_sources_ifdef(CONFIG_ZMK_RGB_UNDERGLOW app PRIVATE src/rgb_underglow.c)

app/Kconfig

@@ -155,10 +155,14 @@ config ZMK_SPLIT
 
 if ZMK_SPLIT
 
+choice ZMK_SPLIT_TYPE
+	prompt "ZMK split type"
+
+if ZMK_BLE
+
 menuconfig ZMK_SPLIT_BLE
 	bool "Split keyboard support via BLE transport"
 	depends on ZMK_BLE
-	default y
 	select BT_USER_PHY_UPDATE
 
 if ZMK_SPLIT_BLE
@@ -199,9 +203,6 @@ config ZMK_SPLIT_BLE_PERIPHERAL_POSITION_QUEUE_SIZE
 	int "Max number of key position state events to queue to send to the central"
 	default 10
 
-config ZMK_USB
-	default n
-
 config BT_MAX_PAIRED
 	default 1
 
@@ -217,6 +218,56 @@ endif
 #ZMK_SPLIT_BLE
 endif
 
+# ZMK_BLE
+endif
+
+if ZMK_USB
+
+menuconfig ZMK_SPLIT_SERIAL
+	bool "Split keyboard support via Serial transport"
+	depends on ZMK_USB
+
+if ZMK_SPLIT_SERIAL
+
+choice ZMK_SPLIT_SERIAL_ROLE
+	prompt "ZMK split serial role"
+
+menuconfig ZMK_SPLIT_SERIAL_ROLE_CENTRAL
+	bool "Central"
+
+menuconfig ZMK_SPLIT_SERIAL_ROLE_PERIPHERAL
+	bool "Peripheral"
+
+if ZMK_SPLIT_SERIAL_ROLE_PERIPHERAL
+
+config ZMK_SPLIT_SERIAL_PERIPHERAL_STACK_SIZE
+	int "Serial split peripheral notify thread stack size"
+	default 512
+
+config ZMK_SPLIT_SERIAL_PERIPHERAL_PRIORITY
+	int "Serial split peripheral notify thread priority"
+	default 5
+
+config ZMK_SPLIT_SERIAL_PERIPHERAL_POSITION_QUEUE_SIZE
+	int "Max number of key position state events to queue to send to the central"
+	default 10
+
+# ZMK_SPLIT_SERIAL_ROLE_PERIPHERAL
+endif
+
+# ZMK_SPLIT_SERIAL_ROLE
+endchoice
+
+# ZMK_SPLIT_SERIAL
+endif
+
+# ZMK_USB
+endif
+
+# ZMK_SPLIT_TYPE
+endchoice
+
+
 #ZMK_SPLIT
 endif
 

app/boards/shields/a_dux/Kconfig.defconfig

@@ -1,19 +1,41 @@
 # Copyright (c) 2021 The ZMK Contributors
 # SPDX-License-Identifier: MIT
 
+if SHIELD_A_DUX_LEFT || SHIELD_A_DUX_RIGHT
+
+if ZMK_BLE || ZMK_USB
+config ZMK_SPLIT
+	default y
+endif
+
 if SHIELD_A_DUX_LEFT
 
 config ZMK_KEYBOARD_NAME
 	default "A. Dux"
 
+if ZMK_BLE
 config ZMK_SPLIT_BLE_ROLE_CENTRAL
 	default y
+endif
 
+if ZMK_USB
+choice ZMK_SPLIT_SERIAL_ROLE
+  default ZMK_SPLIT_SERIAL_ROLE_CENTRAL
+endchoice
 endif
 
-if SHIELD_A_DUX_LEFT || SHIELD_A_DUX_RIGHT
+# SHIELD_A_DUX_LEFT
+endif
 
-config ZMK_SPLIT
-	default y
+if SHIELD_A_DUX_RIGHT
+
+if ZMK_USB
+choice ZMK_SPLIT_SERIAL_ROLE
+  default ZMK_SPLIT_SERIAL_ROLE_PERIPHERAL
+endchoice
+endif
+
+# SHIELD_A_DUX_RIGHT
+endif
 
 endif

app/boards/shields/a_dux/boards/stemcell.overlay

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/ {
+	chosen {
+		zmk,split-serial = &usart1;
+	};
+};
+
+&usart1 {
+	status = "okay";
+};
+
+&kscan0 {
+	input-gpios =
+		<&pro_micro_d  5 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  0 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_a  0 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d 16 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_a  3 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  6 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  2 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>, /* Changed since swapped pins */
+		<&pro_micro_a  1 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d 14 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_a  2 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  7 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  4 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  1 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>, /* TODO: Use 0 if Console is needed */
+		<&pro_micro_d 15 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d 10 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  8 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>,
+		<&pro_micro_d  9 (GPIO_ACTIVE_LOW | GPIO_PULL_UP)>
+	;
+};

app/include/zmk/split/bluetooth/central.h

@@ -5,4 +5,4 @@
 #include <zmk/behavior.h>
 
 int zmk_split_bt_invoke_behavior(uint8_t source, struct zmk_behavior_binding *binding,
-                                 struct zmk_behavior_binding_event event, bool state);
+                                 struct zmk_behavior_binding_event event, bool state);

app/include/zmk/split/bluetooth/service.h

@@ -19,6 +19,3 @@ struct zmk_split_run_behavior_payload {
     struct zmk_split_run_behavior_data data;
     char behavior_dev[ZMK_SPLIT_RUN_BEHAVIOR_DEV_LEN];
 } __packed;
-
-int zmk_split_bt_position_pressed(uint8_t position);
-int zmk_split_bt_position_released(uint8_t position);

app/include/zmk/split/common.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <zephyr/types.h>
+
+#define SPLIT_DATA_LEN 16
+
+#define SPLIT_TYPE_KEYPOSITION 0
+
+typedef struct _split_data_t {
+    uint16_t type;
+    uint8_t data[SPLIT_DATA_LEN];
+    uint16_t crc;
+} split_data_t;
+
+int zmk_split_position_pressed(uint8_t position);
+
+int zmk_split_position_released(uint8_t position);
+

app/src/split/bluetooth/service.c

@@ -19,6 +19,7 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zmk/behavior.h>
 #include <zmk/matrix.h>
 #include <zmk/split/bluetooth/uuid.h>
+#include <zmk/split/common.h>
 #include <zmk/split/bluetooth/service.h>
 
 #define POS_STATE_LEN 16
@@ -141,12 +142,12 @@ int send_position_state() {
     return 0;
 }
 
-int zmk_split_bt_position_pressed(uint8_t position) {
+int zmk_split_position_pressed(uint8_t position) {
     WRITE_BIT(position_state[position / 8], position % 8, true);
     return send_position_state();
 }
 
-int zmk_split_bt_position_released(uint8_t position) {
+int zmk_split_position_released(uint8_t position) {
     WRITE_BIT(position_state[position / 8], position % 8, false);
     return send_position_state();
 }