Be explicit about message preambles.

1 files changed, 101 insertions, 39 deletions

diff --git a/www/AIVDM.txt b/www/AIVDM.txt
index 107d3666..63290585 100644
--- a/www/AIVDM.txt
+++ b/www/AIVDM.txt
@@ -1,6 +1,6 @@
 = AIVDM/AIVDO protocol decoding =
 Eric S. Raymond <esr@thyrsus.com>
-v1.28, Jan 2011
+v1.28+, Jan 2011
 
 This document is mastered in asciidoc format.  If you are reading it in HTML,
 you can find the original at http://gpsd.berlios.de/AIVDM.txt[]
@@ -836,23 +836,53 @@ DAC/FID pairs are assigned separately per message type.
 A list of binary layouts for selected subtypes of message 6 follows.
 (These are not yet implemented by GPSD.)
 
-==== Number of persons on board ====
+==== Number of persons on board (IMO236) ====
 
-A message 6 subtype. DAC = 001 FID = 16 in <<IMO236>>, DAC = 001 FID = 23 
-in <<IMO289>>.  The versions describe trailing padding and length differently,
-but the same 13-bit payload field.
+A message 6 subtype. DAC = 001 FID = 16 in <<IMO236>>.  Fixed length, 72 bits.
 
 [frame="topbot",options="header"]
 |==============================================================================
 |Field   |Len |Description          |Member    |Units
+|0-5     |  6 |Message Type         |type      |Unsigned integer: 8
+|6-7     |  2 |Repeat Indicator     |repeat    |As in Common Navigation Block
+|8-37    | 30 |Source MMSI          |mmsi      |Unsigned integer: 9 digits
+|38-39   |  2 |Spare                |          |Not used
+|40-55   | 16 |DAC/FID              |          |DAC = 001 FID = 16
+|55-69   | 13 |# persons on board   |persons   |Unsigned integer
+|        |    |                     |          |0 = N/A (default)
+|        |    |                     |          |8191 = >= 8191 persons.
+|70-71   |  2 |Spare                |          |Not used
+|==============================================================================
+
+Note that though this is a message 6 subtype, there is no destination address.
+A strikeout in <<IMO236>> suggests that this was originally a subtype of 8.
+It would be good defensive implementation for a decode to accept either.
+
+==== Number of persons on board (IMO289) ====
+
+A message 6 subtype. DAC = 001 FID = 23 in <<IMO289>>. Fixed length, 146 bits.
+
+[frame="topbot",options="header"]
+|==============================================================================
+|Field   |Len |Description          |Member    |Units
+|0-5     |  6 |Message Type         |type      |Unsigned integer: 8
+|6-7     |  2 |Repeat Indicator     |repeat    |As in Common Navigation Block
+|8-37    | 30 |Source MMSI          |mmsi      |Unsigned integer: 9 digits
+|38-39   |  2 |Sequence Number      |seqno     |Unsigned integer 0-3
+|40-69   | 30 |Destination MMSI     |dest_mmsi |Unsigned integer: 9 digits
+|70-70   |  1 |Retransmit flag      |retransmit|0 = no retransmission (default)
+|        |    |                     |          |1 = retransmitted
+|71-71   |  1 |Spare                |          |Not used
 |72-87   | 16 |DAC/FID              |          |DAC = 001 FID = 16
 |88-110  | 13 |# persons on board   |persons   |Unsigned integer
+|        |    |                     |          |0 = N/A (default)
+|        |    |                     |          |8191 = >= 8191 persons.
+|111-146 | 35 |Spare                |          |Not used
 |==============================================================================
 
-FID type 16 is in use; FID23 is a proposed update for it in <<IMO289>>.
-
-The value 0 (the default) means the information is not available. The value
-8191 indicates 8191 or more persons.
+<<IMO289>> claims this message is 136 bits long, but the field lengths
+sum to 146.  It would be good practice to accept either length and
+ignore trailing padding.
 
 ==== Dangerous Cargo Indication ====
 
@@ -863,6 +893,14 @@ with a different layout, not reported in use and deprecated in <<IMO289>>.
 [frame="topbot",options="header"]
 |==============================================================================
 |Field   |Len |Description          |Member    |Units
+|0-5     |  6 |Message Type         |type      |Unsigned integer: 8
+|6-7     |  2 |Repeat Indicator     |repeat    |As in Common Navigation Block
+|8-37    | 30 |Source MMSI          |mmsi      |Unsigned integer: 9 digits
+|38-39   |  2 |Sequence Number      |seqno     |Unsigned integer 0-3
+|40-69   | 30 |Destination MMSI     |dest_mmsi |Unsigned integer: 9 digits
+|70-70   |  1 |Retransmit flag      |retransmit|0 = no retransmission (default)
+|        |    |                     |          |1 = retransmitted
+|71-71   |  1 |Spare                |          |Not used
 |72-87   | 16 |DAC/FID              |          |DAC = 001 FID = 25
 |88-89   |  2 |Unit of Quantity     |unit      |cargounit
 |90-99   | 10 |Amount of Cargo      |amount    |Unsigned integer
@@ -913,7 +951,15 @@ via the Message Linkage ID field.
 
 [frame="topbot",options="header"]
 |==============================================================================
-|Field   |Len    |Description          |Member      |Units
+|Field   |Len    |Description          |Member    |Units
+|0-5     |  6    |Message Type         |type      |Unsigned integer: 8
+|6-7     |  2    |Repeat Indicator     |repeat    |As in Common Navigation Block
+|8-37    | 30    |Source MMSI          |mmsi      |Unsigned integer: 9 digits
+|38-39   |  2    |Sequence Number      |seqno     |Unsigned integer 0-3
+|40-69   | 30    |Destination MMSI     |dest_mmsi |Unsigned integer: 9 digits
+|70-70   |  1    |Retransmit flag      |retransmit|0 = no retransmission (default)
+|        |       |                     |          |1 = retransmitted
+|71-71   |  1    |Spare                |          |Not used
 |72-87   | 16    |DAC/FID              |            |DAC = 001 FID = 30
 |88-97   | 10    |Message Linkage ID   |linkage     |Unsigned integer
 |98-?    | 6-930 |Description          |description |String
@@ -927,22 +973,30 @@ A message 6 subtype. DAC = 001 FID = 32. Fixed length: 350 bits.
 
 [frame="topbot",options="header"]
 |==============================================================================
-|Field   |Len |Description            |Member   |Units
-|72-87   | 16 |DAC/FID                |         |DAC = 001 FID = 32
-|88-91   |  4 |Month                  |month    |1-12; 0 = N/A (default)
-|92-96   |  5 |Day                    |day      |1-31; 0 = N/A (default)
-|97-121  | 25 |Longitude              |lon      |Signed: unit minutes * 0.001
-|        |    |                       |         |181000 = N/A (default)
-|122-145 | 24 |Latitude               |lat      |Signed: unit minutes * 0.001
-|        |    |                       |         |91000 = N/A (default)
-|146-150 |  5 |From UTC Hour          |from_hour|0-23, 24 = N/A (default)
-|151-156 |  6 |From UTC Minute        |from_min |0-59, 60 = N/A (default)
-|157-161 |  5 |To UTC Hour            |to_hour  |0-23, 24 = N/A (default)
-|162-167 |  6 |To UTC Minute          |to_min   |0-59, 60 = N/A (default)
-|168-176 |  9 |Current Dir. Predicted |cdir     |0-359 deg, 360-N/A (default)
-|177-186 |  9 |Current Speed Predicted|cspeed   |0-250, uniits of 0.1 knots.
-|        |    |                       |         |251 = speed >= 25.1 knots
-|        |    |                       |         |255 = N/A (default)
+|Field   |Len |Description            |Member    |Units
+|0-5     |  6 |Message Type           |type      |Unsigned integer: 8
+|6-7     |  2 |Repeat Indicator       |repeat    |As in Common Navigation Block
+|8-37    | 30 |Source MMSI            |mmsi      |Unsigned integer: 9 digits
+|38-39   |  2 |Sequence Number        |seqno     |Unsigned integer 0-3
+|40-69   | 30 |Destination MMSI       |dest_mmsi |Unsigned integer: 9 digits
+|70-70   |  1 |Retransmit flag        |retransmit|0 = no retransmission (default)
+|        |    |                       |          |1 = retransmitted
+|71-71   |  1 |Spare                  |          |Not used
+|72-87   | 16 |DAC/FID                |          |DAC = 001 FID = 32
+|88-91   |  4 |Month                  |month     |1-12; 0 = N/A (default)
+|92-96   |  5 |Day                    |day       |1-31; 0 = N/A (default)
+|97-121  | 25 |Longitude              |lon       |Signed: unit minutes * 0.001
+|        |    |                       |          |181000 = N/A (default)
+|122-145 | 24 |Latitude               |lat       |Signed: unit minutes * 0.001
+|        |    |                       |          |91000 = N/A (default)
+|146-150 |  5 |From UTC Hour          |from_hour |0-23, 24 = N/A (default)
+|151-156 |  6 |From UTC Minute        |from_min  |0-59, 60 = N/A (default)
+|157-161 |  5 |To UTC Hour            |to_hour   |0-23, 24 = N/A (default)
+|162-167 |  6 |To UTC Minute          |to_min    |0-59, 60 = N/A (default)
+|168-176 |  9 |Current Dir. Predicted |cdir      |0-359 deg, 360-N/A (default)
+|177-186 |  9 |Current Speed Predicted|cspeed    |0-250, uniits of 0.1 knots.
+|        |    |                       |          |251 = speed >= 25.1 knots
+|        |    |                       |          |255 = N/A (default)
 |=============================================================================
 
 The group of fields from longitude on may repeat twice more to convey up to
@@ -1035,7 +1089,7 @@ under type 6.
 FID types 11-15 are being phased out and are not to be used after 1
 Jan 2013.The deprecated IMO236 1/11 has a different binary layout from
 the IMO289 1/31.  FID type 17 is in use; there is a proposed
-updates for tit in <<IMO289>>.
+update for it in <<IMO289>>.
 
 Breakdowns of selected Message 8 subtypes from <<IMO289>> follow.
 (These are not yet implemented by GPSD.)
@@ -1050,14 +1104,18 @@ it is titled "Pseudo-AIS Targets".
 
 [frame="topbot",options="header"]
 |==============================================================================
-|Field   |Len    |Description          |Member      |Units
-|72-87   | 16    |DAC/FID              |            |DAC = 001 FID = 17
-|88-89   |  2    |Identifier type      |idtype      |0 = id is the MMSI number
-|        |       |                     |            |1 = id is the IMO number
-|        |       |                     |            |2 = id is the call sign
-|        |       |                     |            |3 = Other (default)
-|90-151  | 42    |Target identifier    |See below   |Target ID data. 
-|152-155 |  4    |Spare                |            |Not used
+|Field   |Len |Description          |Member     |Units
+|0-5     |  6 |Message Type         |type       |Unsigned integer: 8
+|6-7     |  2 |Repeat Indicator     |repeat     |As in Common Navigation Block
+|8-37    | 30 |Source MMSI          |mmsi       |Unsigned integer: 9 digits
+|38-39   |  2 |Spare                |           |Not used
+|40-55   | 16 |DAC/FID              |            |DAC = 001 FID = 17
+|56-57   |  2 |Identifier type      |idtype      |0 = id is the MMSI number
+|        |    |                     |            |1 = id is the IMO number
+|        |    |                     |            |2 = id is the call sign
+|        |    |                     |            |3 = Other (default)
+|58-99   | 42 |Target identifier    |See below   |Target ID data. 
+|100-103 |  4 |Spare                |            |Not used
 |==============================================================================
 
 The interpretation of the target idenifier field depends on the ppreceding type
@@ -1076,7 +1134,7 @@ field groups) to represent up to 4 targets.
 
 ==== Text description (broadcast) ====
 
-A message 8 subtype. DAC = 001 FID = 29. Variable length: 104-1028 bits.
+A message 8 subtype. DAC = 001 FID = 29. Variable length: 72-1034 bits.
 
 Intended to be used to associate a text annotation with another message 
 via the Message Linkage ID field.
@@ -1084,9 +1142,13 @@ via the Message Linkage ID field.
 [frame="topbot",options="header"]
 |==============================================================================
 |Field   |Len    |Description          |Member      |Units
-|72-87   | 16    |DAC/FID              |            |DAC = 001 FID = 29
-|88-97   | 10    |Message Linkage ID   |linkage     |Unsigned integer
-|98-?    | 6-930 |Description          |description |String
+|0-5     |  6    |Message Type         |type        |Unsigned integer: 8
+|6-7     |  2    |Repeat Indicator     |repeat      |As in Common Navigation Block
+|8-37    | 30    |Source MMSI          |mmsi        |Unsigned integer: 9 digits
+|38-39   |  2    |Spare                |            |Not used
+|40-55   | 16    |DAC/FID              |            |DAC = 001 FID = 29
+|56-65   | 10    |Message Linkage ID   |linkage     |Unsigned integer
+|66-?    | 6-930 |Description          |description |String
 |==============================================================================
 
 There is an equivalent subtype of message 6 that is an addressed description.