Add details about updating diag requests.

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

diff --git a/README.md b/README.md
index a56971e..2be7c10 100644 (file)
--- a/README.md
+++ b/README.md
@@ -42,6 +42,117 @@ is sent as a JSON object, separated by newlines. The format of each object is:
   a hexidecimal number in a string. Many JSON parser cannot handle 64-bit
   integers, which is why we are not using a numerical data type.
 
+## Diagnostic Messages
+
+### Requests
+
+A request to add or update a diagnostic request is sent to a vehicle interface
+with this command format:
+
+    { "command": "diagnostic_request",
+      "request": {
+          "bus": 1,
+          "id": 1234,
+          "mode": 1,
+          "pid": 5,
+          "payload": "0x1234",
+          "parse_payload": true,
+          "factor": 1.0,
+          "offset": 0,
+          "frequency": 1
+        }
+      }
+    }
+
+**bus** - the numerical identifier of the CAN bus where this request should be
+    sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
+
+**id** - the CAN arbitration ID for the request.
+
+**mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
+    standardized modes).
+
+**pid** - (optional) the PID for the request, if applicable.
+
+**payload** - (optional) up to 7 bytes of data for the request's payload
+    represented as a hexidecimal number in a string. Many JSON parser cannot
+    handle 64-bit integers, which is why we are not using a numerical data type.
+
+**parse_payload** - (optional, false by default) if true, the complete payload in the
+    response message will be parsed as a number and returned in the 'value' field of
+    the response. The 'payload' field will be omitted in responses with a
+    'value'.
+
+**factor** - (optional, 1.0 by default) if `parse_payload` is true, the value in
+    the payload will be multiplied by this factor before returning. The `factor`
+    is applied before the `offset`.
+
+**offset** - (optional, 0 by default) if `parse_payload` is true, this offset
+    will be added to the value in the payload before returning. The `offset` is
+    applied after the `factor`.
+
+**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.
+
+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.
+
+TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion
+functions - that may need a different output format
+
+If you're just requesting a PID, you can use this minimal field set for the
+`request` object:
+
+    {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
+
+### Responses
+
+    {"bus": 1,
+      "id": 1234,
+      "mode": 1,
+      "pid": 5,
+      "success": true,
+      "negative_response_code": 17,
+      "payload": "0x1234",
+      "parsed_payload": 4660}
+
+**bus** - the numerical identifier of the CAN bus where this response was
+    received.
+
+**id** - the CAN arbitration ID for this response.
+
+**mode** - the OBD-II mode of the original diagnostic request.
+
+**pid** - (optional) the PID for the request, if applicable.
+
+**success** -  true if the response received was a positive response. If this
+  field is false, the remote node returned an error and the
+  `negative_response_code` field should be populated.
+
+**negative_response_code** - (optional)  If requested node returned an error,
+    `success` will be `false` and this field will contain the negative response
+    code (NRC).
+
+Finally, the `payload` and `value` fields are mutually exclusive:
+
+**payload** - (optional) up to 7 bytes of data returned in the response,
+    represented as a hexadecimal number in a string. Many JSON parser cannot
+    handle 64-bit integers, which is why we are not using a numerical data type.
+
+**value** - (optional) if the response had a payload, this may be the
+    payload interpreted as an integer and transformed with a factor and offset
+    provided with the request.
+
+The response to a simple PID request would look like this:
+
+    {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
+
+TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper
+conversion functions so the response here included the actual transformed value
+of the pid and a human readable name
+
 ## Trace File Format
 
 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,