Clarify that 'newline' in trace file may or may not have \r.

[apps/agl-service-can-low-level.git] / README.md

diff --git a/README.md b/README.md
index aa44b05..f26c5d1 100644 (file)
--- a/README.md
+++ b/README.md
@@ -3,16 +3,22 @@
 This specification is a part of the [OpenXC platform][OpenXC].
 
 An OpenXC vehicle interface sends generic vehicle data over one or more output
-interfaces (e.g. USB or Bluetooth) as JSON objects, separated by newlines.
+interfaces (e.g. USB or Bluetooth) as JSON or Protocol Buffers (protobuf).
 
-There are two valid message types - single valued and evented.
+This document describes the JSON format and includes a high level description of
+each type and field. Each JSON message published by a VI is delimited with a
+`\0` character.
+
+The Protocol Buffer format is specified in the file `openxc.proto`. Those are
+published using the standard length-delimited method (any protobuf library
+should support this).
+
+## Single Valued
 
 There may not be a 1:1 relationship between input and output signals - i.e. raw
 engine timing CAN signals may be summarized in an "engine performance" metric on
 the abstract side of the interface.
 
-## Single Valued
-
 The expected format of a single valued message is:
 
     {"name": "steering_wheel_angle", "value": 45}
@@ -28,8 +34,7 @@ discrete pieces of information in the measurement.
 
 ## Raw CAN Message format
 
-An OpenXC vehicle interface may also output raw CAN messages. Each CAN message
-is sent as a JSON object, separated by newlines. The format of each object is:
+The format for a raw CAN message:
 
     {"bus": 1, "id": 1234, "value": "0x12345678"}
 
@@ -97,7 +102,8 @@ with this command format:
   in the VI for longer.
 
 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
-    request. To send a single request, set this to 0 or leave it out.
+    request. To send a single non-recurring request, set this to 0 or leave it
+    out.
 
 **decoded_type** - (optional, defaults to "obd2" if the request is a recognized
 OBD-II mode 1 request, otherwise "none") If specified, the valid values are
@@ -105,10 +111,23 @@ OBD-II mode 1 request, otherwise "none") If specified, the valid values are
 OBD-II specification and returned in the `value` field. Set this to `none` to
 manually override the OBD-II decoding feature for a known PID.
 
-The `bus+id+mode+pid` key is unique, so if you send a create request with that
-key twice, it'll overwrite the existing one (i.e. it will change the frequency,
-the only other parameter). To cancel a recurring request, send this command with
-the frequency set to 0.
+A diagnostic request's `bus`, `id`, `mode` and `pid` (or lack of a `pid`)
+combine to create a unique key to identify a recurring request. This means that
+you cannot simultaneosly have recurring requests at 2Hz and 5Hz for the same PID
+from the same ID.
+
+If you send a new `diagnostic_request` command with a `bus + id + mode + pid`
+key matching an existing recurring request, it will update it with whatever
+other parameters you've provided (e.g. it will change the frequency if you
+specify one).
+
+To cancel a recurring request, send a `diagnostic_request` command with the
+matching request information (i.e. the `bus`, `id`, `mode` and `pid`) but a
+frequency of 0.
+
+Non-recurring requests may have the same `bus+id+mode(+pid)` key as a recurring
+request, and they will co-exist without issue. As soon as a non-recurring
+request is either completed or times out, it is removed from the active list.
 
 If you're just requesting a PID, you can use this minimal field set for the
 `request` object:
@@ -197,7 +216,8 @@ MAC address of an included Bluetooth module) into into the outgoing data stream.
 ## Trace File Format
 
 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
-separated by newlines.
+separated by newlines (which may be either `\r\n` or `\n`, depending on the
+platform the trace file was recorded).
 
 The first line may be a metadata object, although this is optional: