Behaviours: add key-tap behavior

This is a solution for keys that use the same keycode but different
modifiers (see #1076 as an example, also { and [ or ] and } might occur
quite often).

The new key behavior introduced here is a simple tap that immediately
sends a release event, so that a keypress of the same keycode with a
different modifier can be detected immediately.

app/CMakeLists.txt

@@ -39,6 +39,7 @@ if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
   target_sources(app PRIVATE src/hid.c)
   target_sources(app PRIVATE src/behaviors/behavior_key_press.c)
   target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_KEY_TOGGLE app PRIVATE src/behaviors/behavior_key_toggle.c)
+  target_sources(app PRIVATE src/behaviors/behavior_key_tap.c)
   target_sources(app PRIVATE src/behaviors/behavior_hold_tap.c)
   target_sources(app PRIVATE src/behaviors/behavior_sticky_key.c)
   target_sources(app PRIVATE src/behaviors/behavior_caps_word.c)

app/dts/behaviors.dtsi

@@ -1,5 +1,6 @@
 #include <behaviors/key_press.dtsi>
 #include <behaviors/key_toggle.dtsi>
+#include <behaviors/key_tap.dtsi>
 #include <behaviors/transparent.dtsi>
 #include <behaviors/none.dtsi>
 #include <behaviors/mod_tap.dtsi>
@@ -18,4 +19,4 @@
 #include <behaviors/caps_word.dtsi>
 #include <behaviors/key_repeat.dtsi>
 #include <behaviors/backlight.dtsi>
-#include <behaviors/macros.dtsi>
+#include <behaviors/macros.dtsi>

app/dts/behaviors/key_tap.dtsi

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/ {
+	behaviors {
+		/omit-if-no-ref/ kt: behavior_key_tap {
+			compatible = "zmk,behavior-key-tap";
+			label = "KEY_TAP";
+			#binding-cells = <1>;
+		};
+	};
+};

app/dts/bindings/behaviors/zmk,behavior-key-tap.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2022 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Key press/immediate release behavior
+
+compatible: "zmk,behavior-key-tap"
+
+include: one_param.yaml

app/src/behaviors/behavior_key_tap.c

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#define DT_DRV_COMPAT zmk_behavior_key_tap
+
+#include <device.h>
+#include <drivers/behavior.h>
+#include <logging/log.h>
+
+#include <zmk/event_manager.h>
+#include <zmk/events/keycode_state_changed.h>
+#include <zmk/behavior.h>
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+static int behavior_key_tap_init(const struct device *dev) { return 0; };
+
+static int on_keymap_binding_pressed(struct zmk_behavior_binding *binding,
+                                     struct zmk_behavior_binding_event event) {
+    LOG_DBG("position %d keycode 0x%02X", event.position, binding->param1);
+    int ret = 0;
+    ret = ZMK_EVENT_RAISE(zmk_keycode_state_changed_from_encoded(binding->param1, true, event.timestamp));
+    if(ret != 0) {
+        return 0;
+    }
+    return ZMK_EVENT_RAISE(zmk_keycode_state_changed_from_encoded(binding->param1, false, event.timestamp));
+
+}
+
+static int on_keymap_binding_released(struct zmk_behavior_binding *binding,
+                                      struct zmk_behavior_binding_event event) {
+    LOG_DBG("position %d keycode 0x%02X", event.position, binding->param1);
+    return 0;
+}
+
+static const struct behavior_driver_api behavior_key_tap_driver_api = {
+    .binding_pressed = on_keymap_binding_pressed, .binding_released = on_keymap_binding_released};
+
+#define KT_INST(n)                                                                                 \
+    DEVICE_DT_INST_DEFINE(n, behavior_key_tap_init, device_pm_control_nop, NULL, NULL,           \
+                          APPLICATION, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,                        \
+                          &behavior_key_tap_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(KT_INST)