diff --git a/app/CMakeLists.txt b/app/CMakeLists.txt
index 0891364b..0c6412d6 100644
--- a/app/CMakeLists.txt
+++ b/app/CMakeLists.txt
@@ -48,6 +48,7 @@ if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_MACRO app PRIVATE src/behaviors/behavior_macro.c)
target_sources(app PRIVATE src/behaviors/behavior_momentary_layer.c)
target_sources(app PRIVATE src/behaviors/behavior_mod_morph.c)
+ target_sources(app PRIVATE src/behaviors/behavior_antecedent_morph.c)
target_sources(app PRIVATE src/behaviors/behavior_outputs.c)
target_sources(app PRIVATE src/behaviors/behavior_toggle_layer.c)
target_sources(app PRIVATE src/behaviors/behavior_to_layer.c)
diff --git a/app/dts/bindings/behaviors/zmk,behavior-antecedent-morph.yaml b/app/dts/bindings/behaviors/zmk,behavior-antecedent-morph.yaml
new file mode 100644
index 00000000..cf156463
--- /dev/null
+++ b/app/dts/bindings/behaviors/zmk,behavior-antecedent-morph.yaml
@@ -0,0 +1,19 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Antecedent Morph Behavior
+
+compatible: "zmk,behavior-antecedent-morph"
+
+include: zero_param.yaml
+
+properties:
+ bindings:
+ type: phandle-array
+ required: true
+ antecedents:
+ type: array
+ required: true
+ max-delay-ms:
+ type: int
+ default: -1
diff --git a/app/src/behaviors/behavior_antecedent_morph.c b/app/src/behaviors/behavior_antecedent_morph.c
new file mode 100644
index 00000000..0a38ff9e
--- /dev/null
+++ b/app/src/behaviors/behavior_antecedent_morph.c
@@ -0,0 +1,165 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#define DT_DRV_COMPAT zmk_behavior_antecedent_morph
+
+#include <zephyr/device.h>
+#include <drivers/behavior.h>
+#include <zephyr/logging/log.h>
+#include <zmk/behavior.h>
+
+#include <zmk/event_manager.h>
+#include <zmk/events/keycode_state_changed.h>
+#include <zmk/hid.h>
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+#if DT_HAS_COMPAT_STATUS_OKAY(DT_DRV_COMPAT)
+
+// Configuration struct per instance
+struct behavior_antecedent_morph_config {
+ int serial;
+ int max_delay_ms;
+ struct zmk_behavior_binding normal_binding;
+ struct zmk_behavior_binding morph_binding;
+ int32_t antecedents_len;
+ int32_t antecedents[];
+};
+
+// Data struct per instance
+struct behavior_antecedent_morph_data {
+ struct zmk_behavior_binding *pressed_binding;
+};
+
+// Data shared by all instances
+static int32_t code_released; // most recently released key code (with implicit mods, usage page and keycode)
+static int64_t time_released; // time stamp in milli-seconds of that release
+
+static int antecedent_morph_keycode_state_changed_listener(const zmk_event_t *eh);
+
+ZMK_LISTENER(behavior_antecedent_morph, antecedent_morph_keycode_state_changed_listener);
+ZMK_SUBSCRIPTION(behavior_antecedent_morph,zmk_keycode_state_changed);
+
+// Capture all key press and release events in order to record the most recently released key code.
+// Note that the event structure gives us the keycode (16 bit), the usage page (8 bit) and the implicit modifiers (8 bit),
+// but not the explicit modifiers. If the keymap contains the binding "&kp RA(Y)", for example, then right-alt is an
+// implicit modifier so that instead of the Y. the special character Ü is sent.
+// Whether the user is holding down a shift key at that moment, however, i.e. the explicit modifiers, is not known. We could
+// reconstruct this information by tracking the press and release events of the modifier keys (keycodes higher than 0xe0)
+// though.
+// We here record all key release events of non-modifier keys (keycodes less than 0xe0).
+static int antecedent_morph_keycode_state_changed_listener(const zmk_event_t *eh) {
+ struct zmk_keycode_state_changed *ev = as_zmk_keycode_state_changed(eh);
+
+ int32_t code = ((ev->implicit_modifiers & 0xff) << 24) | ((ev->usage_page & 0xff) << 16) | (ev->keycode & 0xffff);
+
+ LOG_DBG("%s keycode %d page %d implicit mods %d explicit mods %d code 0x%08x",ev->state ? "down" : "up",ev->keycode,ev->usage_page,ev->implicit_modifiers,ev->explicit_modifiers,code);
+ if ((!ev->state) && (ev->keycode < 0xe0)) {
+ LOG_DBG("code_released changes from 0x%08x to 0x%08x",code_released,code);
+ code_released = code;
+ time_released = ev->timestamp;
+ }
+
+ return(ZMK_EV_EVENT_BUBBLE);
+}
+
+// When an antecedent morph binding is pressed. we test whether the most recently released key code
+// is among the configured antecedents and whether the corresponding release event was no more
+// than the configured delay time ago.
+static int on_antecedent_morph_binding_pressed(struct zmk_behavior_binding *binding,
+ struct zmk_behavior_binding_event event) {
+ const struct device *dev = device_get_binding(binding->behavior_dev);
+ const struct behavior_antecedent_morph_config *cfg = dev->config;
+ struct behavior_antecedent_morph_data *data = dev->data;
+ bool morph = false;
+
+ if (data->pressed_binding != NULL) {
+ LOG_ERR("Can't press the same antecedent-morph twice");
+ return -ENOTSUP;
+ }
+
+ LOG_DBG("press serial no. %d when code_released 0x%08x delay %dms explicit_mods 0x%02x",cfg->serial,code_released,(int32_t)(event.timestamp-time_released),zmk_hid_get_explicit_mods());
+ for (int i=0;i<cfg->antecedents_len;i++) {
+ if (code_released == cfg->antecedents[i]) {
+ morph = true;
+ }
+ }
+ if ((morph) && ((int32_t)(event.timestamp-time_released)) < cfg->max_delay_ms) {
+ LOG_DBG("morph condition satisfied");
+ data->pressed_binding = (struct zmk_behavior_binding *)&cfg->morph_binding;
+ } else {
+ data->pressed_binding = (struct zmk_behavior_binding *)&cfg->normal_binding;
+ }
+ return behavior_keymap_binding_pressed(data->pressed_binding, event);
+}
+
+static int on_antecedent_morph_binding_released(struct zmk_behavior_binding *binding,
+ struct zmk_behavior_binding_event event) {
+ const struct device *dev = device_get_binding(binding->behavior_dev);
+ const struct behavior_antecedent_morph_config *cfg = dev->config;
+ struct behavior_antecedent_morph_data *data = dev->data;
+
+ if (data->pressed_binding == NULL) {
+ LOG_ERR("Antecedent-morph already released");
+ return -ENOTSUP;
+ }
+
+ LOG_DBG("release serial %d",cfg->serial);
+
+ struct zmk_behavior_binding *pressed_binding = data->pressed_binding;
+ data->pressed_binding = NULL;
+ int err;
+ err = behavior_keymap_binding_released(pressed_binding, event);
+ return err;
+}
+
+static const struct behavior_driver_api behavior_antecedent_morph_driver_api = {
+ .binding_pressed = on_antecedent_morph_binding_pressed,
+ .binding_released = on_antecedent_morph_binding_released,
+};
+
+static int behavior_antecedent_morph_init(const struct device *dev) {
+
+ const struct behavior_antecedent_morph_config *cfg = dev->config;
+
+ LOG_DBG("serial no. %d has got %d antecedents.",cfg->serial,cfg->antecedents_len);
+ for (int i=0; i<cfg->antecedents_len;i++) {
+ LOG_DBG("antedecent no. %d is 0x%08x.",i,cfg->antecedents[i]);
+ }
+
+ code_released = 0;
+
+ return 0;
+}
+
+#define _TRANSFORM_ENTRY(idx, node) \
+ { \
+ .behavior_dev = DT_PROP(DT_INST_PHANDLE_BY_IDX(node, bindings, idx), label), \
+ .param1 = COND_CODE_0(DT_INST_PHA_HAS_CELL_AT_IDX(node, bindings, idx, param1), (0), \
+ (DT_INST_PHA_BY_IDX(node, bindings, idx, param1))), \
+ .param2 = COND_CODE_0(DT_INST_PHA_HAS_CELL_AT_IDX(node, bindings, idx, param2), (0), \
+ (DT_INST_PHA_BY_IDX(node, bindings, idx, param2))), \
+ }
+
+// ??? add to the config the <antecedent> and the <max-delay-ms>
+
+#define KP_INST(n) \
+ static struct behavior_antecedent_morph_config behavior_antecedent_morph_config_##n = { \
+ .serial = n, \
+ .max_delay_ms = DT_INST_PROP(n, max_delay_ms), \
+ .normal_binding = _TRANSFORM_ENTRY(0, n), \
+ .morph_binding = _TRANSFORM_ENTRY(1, n), \
+ .antecedents = DT_INST_PROP(n, antecedents), \
+ .antecedents_len = DT_INST_PROP_LEN(n, antecedents), \
+ }; \
+ static struct behavior_antecedent_morph_data behavior_antecedent_morph_data_##n = {}; \
+ DEVICE_DT_INST_DEFINE(n, behavior_antecedent_morph_init, NULL, &behavior_antecedent_morph_data_##n, \
+ &behavior_antecedent_morph_config_##n, APPLICATION, \
+ CONFIG_KERNEL_INIT_PRIORITY_DEFAULT, &behavior_antecedent_morph_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(KP_INST)
+
+#endif