From fa168027b31e51af34d768eeb7aa62554ce294f3 Mon Sep 17 00:00:00 2001
From: Andy Bauer <knnniggett@hotmail.com>
Date: Sun, 24 Jan 2016 07:45:04 -0600
Subject: [PATCH] Fix PelcoP checksum calculation

---
 scripts/ZoneMinder/lib/ZoneMinder/Control/PelcoP.pm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/scripts/ZoneMinder/lib/ZoneMinder/Control/PelcoP.pm b/scripts/ZoneMinder/lib/ZoneMinder/Control/PelcoP.pm
index c8fafe023..794393644 100644
--- a/scripts/ZoneMinder/lib/ZoneMinder/Control/PelcoP.pm
+++ b/scripts/ZoneMinder/lib/ZoneMinder/Control/PelcoP.pm
@@ -133,8 +133,10 @@ sub sendCmd
 
     my $result = undef;
 
+    # Pelco P protocol checksum is created by XOR'ing the first seven bytes in the message
+    # including the first byte, the STX sync packet
     my $checksum = 0x00;
-    for ( my $i = 1; $i < int(@$cmd); $i++ )
+    for ( my $i = 0; $i < int(@$cmd); $i++ )
     {
         $checksum ^= $cmd->[$i];
     }