From ee742cf8db66fff710f48d8680ad780ae4cc6f72 Mon Sep 17 00:00:00 2001
From: Malcolm Robb <Support@ATTAvionics.com>
Date: Fri, 24 May 2013 12:26:06 +0100
Subject: [PATCH] SBS Output Format changes

Bug fixes in the SBS output code as a result of an EMAIL from Liviu

Some software gets upset if null fields are output where the software is
expecting a valid value. This was being caused by DF0's outputting and
SBS MSG5. MSG5 needs Atert and SPI flags, which are derived from the FS
field. DF0 doesn't have an FS field, so cannot output a MSG5. Change so
that DF0 results in an SBS MSG7.

Also DF17/DF18 metypes 5 to 18 contain raw Lat/Lon data. However they
cannot be decoded into real Lat/Lon values unless both even and odd
parts are available Therefore, when we receive a DF17/DF18 we need to
check that we have successfully decoded the Lat/Lon before we attempt to
send an SBS MSG2 or MSG3. If we don't have a decoded Lat/Lon, send a
MSG7 instead.
---
 dump1090.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/dump1090.c b/dump1090.c
index 9543222..e7eb5b3 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -3534,22 +3534,28 @@ void modesSendSBSOutput(struct modesMessage *mm) {
     //
 
     // Decide on the basic SBS Message Type
-    if ((mm->msgtype ==  0) || (mm->msgtype ==  4) || (mm->msgtype ==  20)) {
+    if        ((mm->msgtype ==  4) || (mm->msgtype == 20)) {
         msgType = 5;
-    } else if ((mm->msgtype ==  5) || (mm->msgtype ==  21)) {
+    } else if ((mm->msgtype ==  5) || (mm->msgtype == 21)) {
         msgType = 6;
-    } else if (mm->msgtype ==  16) {
+    } else if ((mm->msgtype ==  0) || (mm->msgtype == 16)) {
         msgType = 7;
-    } else if (mm->msgtype ==  11) {
+    } else if  (mm->msgtype == 11) {
         msgType = 8;
-    } else if (mm->msgtype !=  17) {
+    } else if ((mm->msgtype != 17) && (mm->msgtype != 18)) {
         return;
-    } else if (mm->metype  == 4) {
+    } else if ((mm->metype >= 1) && (mm->metype <=  4)) {
         msgType = 1;
     } else if ((mm->metype >= 5) && (mm->metype <=  8)) {
-        msgType = 2;
+        if (mm->bFlags & MODES_ACFLAGS_LATLON_VALID)
+            {msgType = 2;}
+        else
+            {msgType = 7;}
     } else if ((mm->metype >= 9) && (mm->metype <= 18)) {
-        msgType = 3;
+        if (mm->bFlags & MODES_ACFLAGS_LATLON_VALID)
+            {msgType = 3;}
+        else
+            {msgType = 7;}
     } else if (mm->metype !=  19) {
         return;
     } else if ((mm->mesub == 1) || (mm->mesub == 2)) {