Download A. Message syntax

Designing an Appliqué Sensor (AS), Rev 0.35
ASIM Messaging Interface
Overview
In the General Satellite Network Model description (A General Satellite Data Model.doc), a Sensor Node
(SN) resides on the general routing network and participates in the SDM or high-speed network. It is
envisioned however, that in the first generation of the model the Sensor Node will be composed of a set of
Applique Sensor Interface Modules (ASIM) connected to a Sensor Manager (SM) using SPA-U interface.
The Sensor Manager will then connect to the general high-speed (SpaceWire, Ethernet, etc.) routing
network and serve as a gateway for sensors into the SDM.
The following diagram is collectively referred to as a Sensor Node:
sensor
ASIM
sensor
ASIM
USB
SM
High-speed routable network
sensor
ASIM
The purpose of sub-dividing a Sensor Node into AS and SMIM components is to simplify the development
of Appliqué Sensors. It is envisioned that an ASIM can be constructed using a single chip microcontroller
such as the Silicon Labs C8051F320 which provides a full USB interface and sufficient flash program
memory to interface to sensor devices and communicate with the Sensor Manager. It also provides a wide
variety of digital and analog ports to support specific interfacing to sensor devices. All network
communications and participation in the data model of the General Satellite Network Model is handled by
the Sensor Manager. A simple messaging protocol between the ASIM and the Sensor Manager is defined
within this document.
A developer of an ASIM must produce two components: First, the ASIM firmware code and second, the
xTEDS document for attached sensors. Both components must reside within AS non-volatile memory. (The
xTEDS document is covered elsewhere.)
ASIM code must be able to control attached sensors and respond to commands from the Sensor Manager.
This document is concerned with requirements of the AS code needed to interface with the Sensor
Manager. As such, this document should be viewed as an Interface Control Document (ICD) for connecting
an ASIM to the Sensor Manager network. This document does not address the interface between the ASIM
and actual sensor(s) which is left to the discretion of the sensor/ASIM designer.
A. Message syntax
Each command arriving from the Sensor Manager will require either a single message response or initiate a
stream of responses.
Messages consist of three (3) fields: Command, Length, and Data. The first byte is the Command,
consisting of a single upper-case ASCII character. Length consists of a 16-bit (2 byte) unsigned integer
Cmd
0
Data…
Length
1
2
3 … (bytes)
representing the number of data bytes. Data bytes are raw byte values. The maximum length of a command
message (from the Sensor Manager) is 64 bytes. The maximum length of a response message (from the
ASIM) is 16k bytes. The length field is most-significant-byte-first.
A. 1 Command messages
The following commands from the Sensor Manager are defined. Some commands may have no effect if not
implemented on a given ASIM (such as Subsystem Control or Device Control). Regardless, every
command should generate a response.
A.1.1 Initialize (I)
Perform any required initialization operations for the sensor(s). This command will always be
given immediately following a power on command. Length field is always 0. Reply expected: Status (S)
A.1.2 Reset (R)
Perform a reset of the sensor device(s) (if defined), perform a warm boot reset of the ASIM code,
and clear the status word. This command will be given following the detection of an anomalous
communication or activity. Length field is always 0. Reply expected: Status (S)
A.1.3 Self test (T)
Perform a self-test of the sensor device(s) and AS controller. Length field is always 0. Reply
expected: Status (S)
A.1.4 Request data message (M)
Request for a data message where length is always 7: and data is a message ID byte (0..255) as
defined in the xTEDS document, followed by an IP address (4 bytes) and a port number (2 bytes).
Reply expected: Data (D) or Status (S) if request cannot be honored. SPECIAL CASE: If a data
message is specified in xTEDS as having an external source (SOURCE=”EXTERNAL”), no reply is
expected directly from the ASIM. The ASIM is responsible for commanding the external device to provide
the appropriate data message(s) through another network connection.
If the associated message is specified in xTEDS as a polled (DATARATE="Polled") message,
this request will result in a single Data (D) reply. If the associated message is specified in xTEDS as a
stream (DATARATE="Stream") message, this request will result in a continuous stream of Data (D)
replies at the rate chosen by the ASIM. In this case, the message stream must be cancelled with a Cancel
(C) command (see A.1.4b). If a message is not defined as either polled or stream in the xTEDS, the default
is polled.
A.1.4b Cancel requested data message stream (C)
Cancel a previous data message stream. Length is always 1, data is a message ID byte. (If no
current message stream is associated with this message ID from a previous Request (M) message, this
command has no effect.
A.1.4c Request a counted data message stream (N)
Request for a data message where length is always 5: The first data byte is the message ID as
defined in the xTEDS document. The remaining 4 data bytes constitute an unsigned 32-bit count. Reply
expected: Data (D) or Status (S) if request cannot be honored.
If the associated message is specified in xTEDS as a polled message, this request will result in a
single Data (D) reply regardless of the given count. If the associated message is specified in xTEDS as a
stream message, this request will result in a continuous stream of Data (D) replies at the rate chosen by the
ASIM for the requested count. In this case, the message stream will automatically cancel after the count is
reached and the Cancel (C) command is not required. However, the Cancel (C) command can be utilized to
prematurely cancel or abort a counted data message stream.
A.1.5 Power on (P)
Power up sensor device(s) to operational mode. Note that only one power-on command is
available. If an AS hosts more than one device, individual devices are expected to be controlled using
Subsystem and Device commands. Length field is always 0. Reply expected: Status (S)
A.1.6 Power down (F)
Power down sensor device(s) to idle mode. Note that only one power-on command is available. If
an AS hosts more than one device, individual devices are expected to be controlled using Subsystem and
Device commands. Length field is always 0. Reply expected: Status (S)
A.1.7 Request Version (U)
Request the version number of this ASIM Command Interpreter. Length field is always 0. Reply
expected: Version(V).
A.1.8 Command Message (V)
Device command message. In this command, length is the length of the command message. Here
data consists of the message name (8 bytes) followed by parameter bytes as defined in the xTEDS
document. If a command message has no parameter bytes, the length will be 8. Reply expected: Status (S).
A.1.9 Read xTEDS (X)
Read xTEDS. Length field is always 0. Reply expected: xTEDS (X) or Status (S) if the request
cannot be honored.
A.1.10 Time at the Tone (O)
The time at the next sync pulse is given in the data field in 8 bytes: time(sec) (4 bytes) + time
(usec) (4 bytes). When the next sync is received the current time is to be replaced with the time at the tone.
Length field is always 8. Reply expected: Status(S).
A.1.11 Development (>0x8F)
These command code values are reserved for sensor developers and will not be used in future
expansions of the ASI.
A.2 Response messages
A message command field used in an ASIM response consists of a single upper-case letter. The following
commands are defined;
A.2.1 Status (S)
A status reply contains an 8-bit (one byte) status word. In this message, length is always 1.
A.2.2 Data (D)
In a data reply, length is the length of the data reply message plus one byte and data represents
two components: The first data byte is the message ID (0..255). The remaining message content is
as defined in the xTEDS definition for the message. For example, if an xTEDS-defined message
consists of 8 data bytes, the length field of this reply would be 9 bytes; one byte for the message
ID and 8 data bytes.
A.2.3 xTEDS (X)
In an xTEDS reply, length is the byte length of the xTEDS document and data represents the text
of the entire document.
A.2.4 Version (V )
Aversion reply contains an 8-bit (one byte) version. In this message, length is always 1.
B. Message timeouts
The Sensor Manager will expect a reply to a command message within TBD seconds. If a reply times out,
the Sensor Manager will issue a Reset (R) message. If two successive Reset messages time out, the Sensor
Manager will abandon the AS and ignore any further communications.
C. Status
An 8-bit status word must be maintained by the AS.
Bit
description
0 (MSB)
Error (OR of bits 1, 2)
1
Illegal or unrecognized command. (Cleared upon transmission)
2
Self-test failure. (Cleared upon transmission)
3
Mode (0 for idle, 1 for operation)
4
(available)
5
(available)
6
(available)
7 (LSB)
(available)