diff --git a/libraries/AP_HAL_ChibiOS/GPIO.cpp b/libraries/AP_HAL_ChibiOS/GPIO.cpp
index ac652422a7..69ce1ef034 100644
--- a/libraries/AP_HAL_ChibiOS/GPIO.cpp
+++ b/libraries/AP_HAL_ChibiOS/GPIO.cpp
@@ -26,6 +26,7 @@ static struct gpio_entry {
     bool enabled;
     uint8_t pwm_num;
     ioline_t pal_line;
+    AP_HAL::GPIO::irq_handler_fn_t fn; // callback for GPIO interface
 } _gpio_tab[] = HAL_GPIO_PINS;
 
 #define NUM_PINS ARRAY_SIZE(_gpio_tab)
@@ -48,6 +49,7 @@ static struct gpio_entry *gpio_by_pin_num(uint8_t pin_num, bool check_enabled=tr
 }
 
 static void pal_interrupt_cb(void *arg);
+static void pal_interrupt_cb_functor(void *arg);
 
 GPIO::GPIO()
 {}
@@ -115,19 +117,56 @@ AP_HAL::DigitalSource* GPIO::channel(uint16_t pin)
 extern const AP_HAL::HAL& hal;
 
 /* 
+   Attach an interrupt handler to a GPIO pin number. The pin number
+   must be one specified with a GPIO() marker in hwdef.dat
+ */
+bool GPIO::attach_interrupt(uint8_t pin,
+                            irq_handler_fn_t fn,
+                            INTERRUPT_TRIGGER_TYPE mode)
+{
+    struct gpio_entry *g = gpio_by_pin_num(pin, false);
+    if (!g) {
+        return false;
+    }
+    if (!_attach_interrupt(g->pal_line,
+                           palcallback_t(fn?pal_interrupt_cb_functor:nullptr),
+                           g,
+                           mode)) {
+        return false;
+    }
+    g->fn = fn;
+    return true;
+}
+
+/*
    Attach an interrupt handler to ioline_t
  */
 bool GPIO::_attach_interrupt(ioline_t line, AP_HAL::Proc p, uint8_t mode)
+{
+    return _attach_interrupt(line, palcallback_t(p?pal_interrupt_cb:nullptr), (void*)p, mode);
+}
+
+bool GPIO::attach_interrupt(uint8_t pin,
+                            AP_HAL::Proc proc,
+                            INTERRUPT_TRIGGER_TYPE mode) {
+    struct gpio_entry *g = gpio_by_pin_num(pin, false);
+    if (!g) {
+        return false;
+    }
+    return _attach_interrupt(g->pal_line, proc, mode);
+}
+
+bool GPIO::_attach_interrupt(ioline_t line, palcallback_t cb, void *p, uint8_t mode)
 {
     uint32_t chmode = 0;
     switch(mode) {
-        case HAL_GPIO_INTERRUPT_FALLING:
+        case INTERRUPT_FALLING:
             chmode = PAL_EVENT_MODE_FALLING_EDGE;
             break;
-        case HAL_GPIO_INTERRUPT_RISING:
+        case INTERRUPT_RISING:
             chmode = PAL_EVENT_MODE_RISING_EDGE;
             break;
-        case HAL_GPIO_INTERRUPT_BOTH:
+        case INTERRUPT_BOTH:
             chmode = PAL_EVENT_MODE_BOTH_EDGES;
             break;
         default:
@@ -136,34 +175,25 @@ bool GPIO::_attach_interrupt(ioline_t line, AP_HAL::Proc p, uint8_t mode)
             }
             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;
-        }
+
+    osalSysLock();
+    palevent_t *pep = pal_lld_get_line_event(line);
+    if (pep->cb && p != nullptr) {
+        // the pad is already being used for a callback
         osalSysUnlock();
-    }
-
-    palDisableLineEvent(line);
-    palEnableLineEvent(line, chmode);
-    palSetLineCallback(line, p?pal_interrupt_cb:nullptr, (void*)p);
-    return true;
-}
-
-/* 
-   Attach an interrupt handler to a GPIO pin number. The pin number
-   must be one specified with a GPIO() marker in hwdef.dat
- */
-bool GPIO::attach_interrupt(uint8_t pin, AP_HAL::Proc p, uint8_t mode)
-{
-    struct gpio_entry *g = gpio_by_pin_num(pin, false);
-    if (!g) {
         return false;
     }
-    return _attach_interrupt(g->pal_line, p, mode);
+
+    if (!p) {
+        chmode = PAL_EVENT_MODE_DISABLED;
+    }
+
+    palDisableLineEventI(line);
+    palSetLineCallbackI(line, cb, p);
+    palEnableLineEventI(line, chmode);
+    osalSysUnlock();
+
+    return true;
 }
 
 bool GPIO::usb_connected(void)
@@ -202,3 +232,18 @@ void pal_interrupt_cb(void *arg)
     }
 }
 
+void pal_interrupt_cb_functor(void *arg)
+{
+    const uint32_t now = AP_HAL::micros();
+
+    struct gpio_entry *g = (gpio_entry *)arg;
+    if (g == nullptr) {
+        // what?
+        return;
+    }
+    if (!(g->fn)) {
+        return;
+    }
+    (g->fn)(g->pin_num, palReadLine(g->pal_line), now);
+}
+
diff --git a/libraries/AP_HAL_ChibiOS/GPIO.h b/libraries/AP_HAL_ChibiOS/GPIO.h
index b95aee97d8..99630c7b36 100644
--- a/libraries/AP_HAL_ChibiOS/GPIO.h
+++ b/libraries/AP_HAL_ChibiOS/GPIO.h
@@ -38,9 +38,15 @@ public:
     /* Alternative interface: */
     AP_HAL::DigitalSource* channel(uint16_t n);
 
-    /* Interrupt interface: */
-    bool    attach_interrupt(uint8_t interrupt_num, AP_HAL::Proc p,
-            uint8_t mode);
+    /* Interrupt interface - fast, for RCOutput and SPI radios */
+    bool    attach_interrupt(uint8_t interrupt_num,
+                             AP_HAL::Proc p,
+                             INTERRUPT_TRIGGER_TYPE mode) override;
+
+    /* Interrupt interface - for AP_HAL::GPIO */
+    bool    attach_interrupt(uint8_t pin,
+                             irq_handler_fn_t fn,
+                             INTERRUPT_TRIGGER_TYPE mode) override;
 
     /* return true if USB cable is connected */
     bool    usb_connected(void) override;
@@ -53,6 +59,8 @@ public:
 private:
     bool _usb_connected;
     bool _ext_started;
+
+    bool _attach_interrupt(ioline_t line, palcallback_t cb, void *p, uint8_t mode);
 };
 
 class ChibiOS::DigitalSource : public AP_HAL::DigitalSource {
diff --git a/libraries/AP_HAL_ChibiOS/RCOutput.cpp b/libraries/AP_HAL_ChibiOS/RCOutput.cpp
index 9314fd60de..6c1fe89db9 100644
--- a/libraries/AP_HAL_ChibiOS/RCOutput.cpp
+++ b/libraries/AP_HAL_ChibiOS/RCOutput.cpp
@@ -1271,7 +1271,7 @@ uint16_t RCOutput::serial_read_bytes(uint8_t *buf, uint16_t len)
     palWriteLine(HAL_GPIO_LINE_GPIO54, 1);
 #endif
     
-    if (!((GPIO *)hal.gpio)->_attach_interrupt(line, serial_bit_irq, HAL_GPIO_INTERRUPT_BOTH)) {
+    if (!((GPIO *)hal.gpio)->_attach_interrupt(line, serial_bit_irq, AP_HAL::GPIO::INTERRUPT_BOTH)) {
 #if RCOU_SERIAL_TIMING_DEBUG
         palWriteLine(HAL_GPIO_LINE_GPIO54, 0);
 #endif