feat(studio): Initial RPC infrastructure and subsystems.

* UART and BLE/GATT transports for a protobuf encoded RPC
  request/response protocol.
* Custom framing protocol is used to frame a give message.
* Requests/responses are divided into major "subsystems" which
  handle requests and create response messages.
* Notification support, including mapping local events to RPC
  notifications by a given subsystem.
* Meta responses for "no response" and "unlock needed".
* Initial basic lock state support in a new core section, and allow specifying
  if a given RPC callback requires unlocked state or not.
* Add behavior subsystem with full metadata support and examples of
  using callback to serialize a repeated field without extra stack space needed.

app/CMakeLists.txt

@@ -36,6 +36,7 @@ target_sources_ifdef(CONFIG_ZMK_GPIO_KEY_WAKEUP_TRIGGER app PRIVATE src/gpio_key
 target_sources(app PRIVATE src/events/activity_state_changed.c)
 target_sources(app PRIVATE src/events/position_state_changed.c)
 target_sources(app PRIVATE src/events/sensor_event.c)
+
 target_sources(app PRIVATE src/events/mouse_button_state_changed.c)
 target_sources_ifdef(CONFIG_ZMK_WPM app PRIVATE src/events/wpm_state_changed.c)
 target_sources_ifdef(CONFIG_USB_DEVICE_STACK app PRIVATE src/events/usb_conn_state_changed.c)
@@ -105,4 +106,21 @@ target_sources(app PRIVATE src/main.c)
 add_subdirectory(src/display/)
 add_subdirectory_ifdef(CONFIG_SETTINGS src/settings/)
 
+if (CONFIG_ZMK_STUDIO)
+  # For some reason this is failing if run from a different sub-file.
+  list(APPEND CMAKE_MODULE_PATH ${ZEPHYR_BASE}/modules/nanopb)
+
+  include(nanopb)
+
+  zephyr_nanopb_sources(app
+                        proto/zmk/studio.proto
+                        proto/zmk/meta.proto
+                        proto/zmk/core.proto
+                        proto/zmk/behaviors.proto
+                        proto/zmk/keymap.proto
+                        )
+
+  add_subdirectory(src/studio)
+endif()
+
 zephyr_cc_option(-Wfatal-errors)

app/Kconfig

@@ -252,6 +252,8 @@ rsource "src/split/Kconfig"
 #Basic Keyboard Setup
 endmenu
 
+rsource "src/studio/Kconfig"
+
 menu "Display/LED Options"
 
 rsource "src/display/Kconfig"

app/boards/shields/zmk_uno/boards/nrf52840dk_nrf52840.overlay

@@ -63,4 +63,14 @@ encoder: &qdec0 {
 
         wakeup-sources = <&soft_off_direct_kscan>;
     };
-};
+
+    chosen {
+        zmk,studio-rpc-uart = &studio_uart;
+    };
+};
+
+&zephyr_udc0 {
+    studio_uart: studio_uart {
+        compatible = "zephyr,cdc-acm-uart";
+    };
+};

app/include/linker/zmk-rpc-event-mappers.ld

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2024 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/linker/linker-defs.h>
+
+ITERABLE_SECTION_ROM(zmk_rpc_event_mapper, 4)

app/include/linker/zmk-rpc-subsystem-handlers.ld

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/linker/linker-defs.h>
+
+ITERABLE_SECTION_ROM(zmk_rpc_subsystem_handler, 4)

app/include/linker/zmk-rpc-subsystems.ld

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/linker/linker-defs.h>
+
+ITERABLE_SECTION_RAM(zmk_rpc_subsystem, 4)

app/include/linker/zmk-rpc-transport.ld

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2024 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <zephyr/linker/linker-defs.h>
+
+ITERABLE_SECTION_ROM(zmk_rpc_transport, 4)

app/include/zmk/studio/core.h

@@ -0,0 +1,23 @@
+
+#pragma once
+
+#include <zmk/event_manager.h>
+
+enum zmk_studio_core_lock_state {
+    ZMK_STUDIO_CORE_LOCK_STATE_LOCKED = 0,
+    ZMK_STUDIO_CORE_LOCK_STATE_UNLOCKING = 1,
+    ZMK_STUDIO_CORE_LOCK_STATE_UNLOCKED = 2,
+};
+
+struct zmk_studio_core_lock_state_changed {
+    enum zmk_studio_core_lock_state state;
+};
+
+ZMK_EVENT_DECLARE(zmk_studio_core_lock_state_changed);
+
+enum zmk_studio_core_lock_state zmk_studio_core_get_lock_state(void);
+
+void zmk_studio_core_unlock();
+void zmk_studio_core_lock();
+void zmk_studio_core_initiate_unlock();
+void zmk_studio_core_complete_unlock();

app/include/zmk/studio/rpc.h

@@ -0,0 +1,153 @@
+
+#pragma once
+
+#include <zephyr/sys/iterable_sections.h>
+#include <zephyr/sys/ring_buffer.h>
+
+#include <proto/zmk/studio.pb.h>
+
+#include <zmk/endpoints_types.h>
+#include <zmk/event_manager.h>
+#include <zmk/studio/core.h>
+
+struct zmk_studio_rpc_notification {
+    zmk_Notification notification;
+};
+
+ZMK_EVENT_DECLARE(zmk_studio_rpc_notification);
+
+struct zmk_rpc_subsystem;
+
+typedef zmk_Response(subsystem_func)(const struct zmk_rpc_subsystem *subsys,
+                                     const zmk_Request *req);
+
+typedef zmk_Response(rpc_func)(const zmk_Request *neq);
+
+struct zmk_rpc_subsystem {
+    subsystem_func *func;
+    uint16_t handlers_start_index;
+    uint16_t handlers_end_index;
+    uint8_t subsystem_choice;
+};
+
+struct zmk_rpc_subsystem_handler {
+    rpc_func *func;
+    uint8_t subsystem_choice;
+    uint8_t request_choice;
+    bool secured;
+};
+
+#define ZMK_RPC_NO_RESPONSE() ZMK_RPC_RESPONSE(meta, no_response, true)
+#define ZMK_RPC_SIMPLE_ERR(type)                                                                   \
+    ZMK_RPC_RESPONSE(meta, simple_error, zmk_meta_ErrorConditions_##type)
+
+#define ZMK_RPC_SUBSYSTEM(prefix)                                                                  \
+    zmk_Response subsystem_func_##prefix(const struct zmk_rpc_subsystem *subsys,                   \
+                                         const zmk_Request *req) {                                 \
+        uint8_t which_req = req->subsystem.prefix.which_request_type;                              \
+        LOG_DBG("Got subsystem func for %d", subsys->subsystem_choice);                            \
+                                                                                                   \
+        for (int i = subsys->handlers_start_index; i <= subsys->handlers_end_index; i++) {         \
+            struct zmk_rpc_subsystem_handler *sub_handler;                                         \
+            STRUCT_SECTION_GET(zmk_rpc_subsystem_handler, i, &sub_handler);                        \
+            if (sub_handler->request_choice == which_req) {                                        \
+                if (sub_handler->secured &&                                                        \
+                    zmk_studio_core_get_lock_state() != ZMK_STUDIO_CORE_LOCK_STATE_UNLOCKED) {     \
+                    return ZMK_RPC_RESPONSE(meta, simple_error,                                    \
+                                            zmk_meta_ErrorConditions_UNLOCK_REQUIRED);             \
+                }                                                                                  \
+                return sub_handler->func(req);                                                     \
+            }                                                                                      \
+        }                                                                                          \
+        LOG_ERR("No handler func found for %d", which_req);                                        \
+        return ZMK_RPC_RESPONSE(meta, simple_error, zmk_meta_ErrorConditions_RPC_NOT_FOUND);       \
+    }                                                                                              \
+    STRUCT_SECTION_ITERABLE(zmk_rpc_subsystem, prefix##_subsystem) = {                             \
+        .func = subsystem_func_##prefix,                                                           \
+        .subsystem_choice = zmk_Request_##prefix##_tag,                                            \
+    };
+
+#define ZMK_RPC_SUBSYSTEM_HANDLER(prefix, request_id, _secured)                                    \
+    STRUCT_SECTION_ITERABLE(zmk_rpc_subsystem_handler,                                             \
+                            prefix##_subsystem_handler_##request_id) = {                           \
+        .func = request_id,                                                                        \
+        .subsystem_choice = zmk_Request_##prefix##_tag,                                            \
+        .request_choice = zmk_##prefix##_Request_##request_id##_tag,                               \
+        .secured = _secured,                                                                       \
+    };
+
+#define ZMK_RPC_NOTIFICATION(subsys, _type, ...)                                                   \
+    ((zmk_Notification){                                                                           \
+        .which_subsystem = zmk_Notification_##subsys##_tag,                                        \
+        .subsystem =                                                                               \
+            {                                                                                      \
+                .subsys =                                                                          \
+                    {                                                                              \
+                        .which_notification_type = zmk_##subsys##_Notification_##_type##_tag,      \
+                        .notification_type = {._type = __VA_ARGS__},                               \
+                    },                                                                             \
+            },                                                                                     \
+    })
+
+#define ZMK_RPC_RESPONSE(subsys, _type, ...)                                                       \
+    ((zmk_Response){                                                                               \
+        .which_type = zmk_Response_request_response_tag,                                           \
+        .type =                                                                                    \
+            {                                                                                      \
+                .request_response =                                                                \
+                    {                                                                              \
+                        .which_subsystem = zmk_RequestResponse_##subsys##_tag,                     \
+                        .subsystem =                                                               \
+                            {                                                                      \
+                                .subsys =                                                          \
+                                    {                                                              \
+                                        .which_response_type =                                     \
+                                            zmk_##subsys##_Response_##_type##_tag,                 \
+                                        .response_type = {._type = __VA_ARGS__},                   \
+                                    },                                                             \
+                            },                                                                     \
+                    },                                                                             \
+            },                                                                                     \
+    })
+
+typedef int(zmk_rpc_event_mapper_cb)(const zmk_event_t *ev, zmk_Notification *n);
+
+struct zmk_rpc_event_mapper {
+    zmk_rpc_event_mapper_cb *func;
+};
+
+#define ZMK_RPC_EVENT_MAPPER_ADD_LISTENER(_t) ZMK_SUBSCRIPTION(studio_rpc, _t)
+
+#define ZMK_RPC_EVENT_MAPPER(name, _func, ...)                                                     \
+    FOR_EACH_NONEMPTY_TERM(ZMK_RPC_EVENT_MAPPER_ADD_LISTENER, (;), __VA_ARGS__)                    \
+    STRUCT_SECTION_ITERABLE(zmk_rpc_event_mapper, name) = {                                        \
+        .func = _func,                                                                             \
+    };
+
+typedef int (*zmk_rpc_rx_start_stop_func)(void);
+
+typedef void (*zmk_rpc_tx_buffer_notify_func)(struct ring_buf *buf, size_t added, bool message_done,
+                                              void *user_data);
+typedef void *(*zmk_rpc_tx_user_data_func)(void);
+
+struct zmk_rpc_transport {
+    enum zmk_transport transport;
+
+    zmk_rpc_tx_user_data_func tx_user_data;
+    zmk_rpc_tx_buffer_notify_func tx_notify;
+    zmk_rpc_rx_start_stop_func rx_start;
+    zmk_rpc_rx_start_stop_func rx_stop;
+};
+
+struct ring_buf *zmk_rpc_get_tx_buf(void);
+struct ring_buf *zmk_rpc_get_rx_buf(void);
+void zmk_rpc_rx_notify(void);
+
+#define ZMK_RPC_TRANSPORT(name, _transport, _rx_start, _rx_stop, _tx_user_data, _tx_notify)        \
+    STRUCT_SECTION_ITERABLE(zmk_rpc_transport, name) = {                                           \
+        .transport = _transport,                                                                   \
+        .rx_start = _rx_start,                                                                     \
+        .rx_stop = _rx_stop,                                                                       \
+        .tx_user_data = _tx_user_data,                                                             \
+        .tx_notify = _tx_notify,                                                                   \
+    }

app/proto/zmk/.gitignore

@@ -0,0 +1,2 @@
+include/
+src/

app/proto/zmk/behaviors.proto

@@ -0,0 +1,70 @@
+syntax = "proto3";
+
+package zmk.behaviors;
+
+message Request {
+    oneof request_type {
+        bool list_all_behaviors = 1;
+        GetBehaviorDetailsRequest get_behavior_details = 2;
+    }
+}
+
+message GetBehaviorDetailsRequest {
+    uint32 behavior_id = 1;
+}
+
+message Response {
+    oneof response_type {
+        ListAllBehaviorsResponse list_all_behaviors = 1;
+        GetBehaviorDetailsResponse get_behavior_details = 2;
+    }
+}
+
+message ListAllBehaviorsResponse {
+    repeated uint32 behaviors = 1;
+}
+
+message GetBehaviorDetailsResponse {
+    uint32 id = 1;
+    string friendly_name = 2;
+    oneof parameters_type {
+        BehaviorBindingParametersStandard standard = 3;
+        BehaviorBindingParametersCustom custom = 4;
+    }
+}
+
+message BehaviorBindingParametersStandard {
+    BehaviorBindingParameterStandardDomain param1 = 1;
+    BehaviorBindingParameterStandardDomain param2 = 2;
+}
+
+enum BehaviorBindingParameterStandardDomain {
+    NIL = 0;
+    HID_USAGE = 1;
+    LAYER_INDEX = 2;
+    HSV_VALUE = 3;
+}
+
+message BehaviorBindingParametersCustom {
+    repeated BehaviorBindingParametersCustomSet param_sets = 1;
+}
+
+message BehaviorBindingParametersCustomSet {
+    repeated BehaviorParameterValueDescription param1 = 1;
+    repeated BehaviorParameterValueDescription param2 = 2;
+}
+
+message BehaviorParameterValueDescriptionRange {
+    uint32 min = 1;
+    uint32 max = 2;
+}
+
+message BehaviorParameterValueDescription {
+    string name = 1;
+
+    oneof value_type {
+        uint32 constant = 2;
+        BehaviorParameterValueDescriptionRange range = 3;
+        BehaviorBindingParameterStandardDomain standard = 4;
+    }
+}

app/proto/zmk/core.proto

@@ -0,0 +1,29 @@
+syntax = "proto3";
+
+package zmk.core;
+
+enum LockState {
+    ZMK_STUDIO_CORE_LOCK_STATE_LOCKED = 0;
+    ZMK_STUDIO_CORE_LOCK_STATE_UNLOCKING = 1;
+    ZMK_STUDIO_CORE_LOCK_STATE_UNLOCKED = 2;
+}
+
+message Request {
+    oneof request_type {
+        bool get_lock_state = 1;
+        bool request_unlock = 2;
+        bool lock = 3;
+    }
+}
+
+message Response {
+    oneof response_type {
+        LockState get_lock_state = 1;
+    }
+}
+
+message Notification {
+    oneof notification_type {
+        LockState lock_state_changed = 1;
+    }
+}

app/proto/zmk/keymap.proto

@@ -0,0 +1,9 @@
+syntax = "proto3";
+
+package zmk.keymap;
+
+message Request {
+    oneof request_type {
+        bool get_layer_summaries = 1;
+    }
+}