From fb6ab85c4af5d21a2de4d4391050692439a9979e Mon Sep 17 00:00:00 2001
From: Neil McKechnie <neilmck999@gmail.com>
Date: Fri, 27 Aug 2021 21:43:24 +0100
Subject: [PATCH] Add flag to invert DCC Accessory command <a> behaviour

<a addr subaddr 1> command puts a D=1 into the DCC packet for a DCC Accessory Decoder.  This was previously though to correspond to a 'throw' request and a D=0 to a 'close' request.  RCN-213 standard identifies that D=1 is 'close' and D=0 is 'throw', so this change allows CS to be configured to invert the states to conform to the RCN-213 definition.
---
 DCC.cpp          |  3 +++
 DCCEXParser.cpp  |  7 ++++++-
 config.example.h | 10 ++++++++--
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/DCC.cpp b/DCC.cpp
index e3dd921..79c5b19 100644
--- a/DCC.cpp
+++ b/DCC.cpp
@@ -239,6 +239,9 @@ void DCC::updateGroupflags(byte & flags, int16_t functionNumber) {
 }
 
 void DCC::setAccessory(int address, byte number, bool activate) {
+  #ifdef DIAG_IO
+  DIAG(F("DCC::setAccessory(%d,%d,%d)"), address, number, activate);
+  #endif
   // use masks to detect wrong values and do nothing
   if(address != (address & 511))
     return;
diff --git a/DCCEXParser.cpp b/DCCEXParser.cpp
index e4b4d73..91039f7 100644
--- a/DCCEXParser.cpp
+++ b/DCCEXParser.cpp
@@ -27,6 +27,7 @@
 #include "freeMemory.h"
 #include "GITHUB_SHA.h"
 #include "version.h"
+#include "defines.h"
 
 #include "EEStore.h"
 #include "DIAG.h"
@@ -364,8 +365,12 @@ void DCCEXParser::parse(Print *stream, byte *com, RingStream * ringStream)
           || ((subaddress & 0x03) != subaddress)  // invalid subaddress (limit 2 bits ) 
           || ((p[activep]  & 0x01) != p[activep]) // invalid activate 0|1
           ) break; 
-          // TODO: Trigger configurable range of addresses on local VPins.
+          // Honour the configuration option (config.h) which allows the <a> command to be reversed
+#ifdef DCC_ACCESSORY_RCN_213
+          DCC::setAccessory(address, subaddress,p[activep]==0);
+#else
           DCC::setAccessory(address, subaddress,p[activep]==1);
+#endif
         }
         return;
      
diff --git a/config.example.h b/config.example.h
index 6c5c69a..9b1855f 100644
--- a/config.example.h
+++ b/config.example.h
@@ -134,11 +134,17 @@ The configuration file for DCC-EX Command Station
 //
 // According to norm RCN-213 a DCC packet with a 1 is closed/straight
 // and one with a 0 is thrown/diverging.  In DCC++ Classic, and in previous
-// versions of DCC++EX, a throw command was implemented in the packet as 
+// versions of DCC++EX, a turnout throw command was implemented in the packet as 
 // '1' and a close command as '0'. The #define below makes the states
 // match with the norm.  But we don't want to cause havoc on existent layouts,
 // so we define this only for new installations. If you don't want this,
 // don't add it to your config.h.
-#define DCC_TURNOUTS_RCN_213
+//#define DCC_TURNOUTS_RCN_213
+
+// The following #define likewise inverts the behaviour of the <a> command 
+// for triggering DCC Accessory Decoders, so that <a addr subaddr 0> generates a 
+// DCC packet with D=1 (close turnout) and <a addr subaddr 1> generates D=0 
+// (throw turnout).
+//#define DCC_ACCESSORY_RCN_213
 
 /////////////////////////////////////////////////////////////////////////////////////