From 64c8ca514c55562cc832ffa6315238b44ba37a83 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Fri, 3 Aug 2018 09:57:57 +1000
Subject: [PATCH] HAL_ChibiOS: fixed attach_interrupt check

we can't have two handlers on the same pad
---
 libraries/AP_HAL_ChibiOS/GPIO.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/libraries/AP_HAL_ChibiOS/GPIO.cpp b/libraries/AP_HAL_ChibiOS/GPIO.cpp
index c42cc91634..26a2693233 100644
--- a/libraries/AP_HAL_ChibiOS/GPIO.cpp
+++ b/libraries/AP_HAL_ChibiOS/GPIO.cpp
@@ -135,10 +135,21 @@ bool GPIO::_attach_interrupt(ioline_t line, AP_HAL::Proc p, uint8_t mode)
                 return false;
             }
             break;
+    }    
+    if (p) {
+        osalSysLock();
+        palevent_t *pep = pal_lld_get_line_event(line);
+        if (pep->cb) {
+            // the pad is already being used for a callback
+            osalSysUnlock();
+            return false;
+        }
+        osalSysUnlock();
     }
+
     palDisableLineEvent(line);
     palEnableLineEvent(line, chmode);
-    palSetLineCallback(line, pal_interrupt_cb, (void*)p);
+    palSetLineCallback(line, p?pal_interrupt_cb:nullptr, (void*)p);
     return true;
 }