Debugger stuff. Lots of wasted work :/

src/xenia/debug/proto/xdp_protocol.md

@@ -0,0 +1,44 @@
+XDP: Xenia Debug Protocol
+--------------------------
+
+## Overview
+
+### General
+
+* Packets flow in both directions (client and server).
+* Each packet is length-prefixed (exclusive) and tagged with a type.
+* The entire protocol is fully asynchronous, and supports both request/response
+  style RPCs as well as notifications.
+* Request/response RPCs are matched on ID and multiple are allowed to be in
+  flight at a time.
+* Notifications may come in any order.
+
+### Server
+
+The debug server is single threaded and processes commands as a FIFO. This
+means that all requests will be responded to in the order they are received.
+
+### Client
+
+TODO
+
+## Packet Structure
+
+Each packet consists of a length, type, and request ID. The length denotes
+the total number of bytes within the packet body, excluding the packet header.
+The request ID is an opaque value sent by the client when making a request and
+the server returns whatever the ID is when it responds to that request. The ID
+is unused for notifications.
+
+```
+struct Packet {
+  uint16_t packet_type;
+  uint16_t request_id;
+  uint32_t body_length;
+  uint8_t body[body_length];
+};
+```
+
+## Packets
+
+TODO(benvanik): document the various types, etc.