Small bugfix to GPIO.c -- Oops!

app/modules/gpio.c

@@ -62,22 +62,27 @@ static void gpio_intr_callback_task (task_param_t param, uint8 priority)
 static int lgpio_trig( lua_State* L )
 {
   unsigned pin = luaL_checkinteger( L, 1 );
-  static const char * const opts[] = {"", "up", "down", "both", "low", "high"};
+  int old_pin_ref = gpio_cb_ref[pin];
+  static const char * const opts[] = {"none", "up", "down", "both", "low", "high", NULL};
   static const int opts_type[] = {
     GPIO_PIN_INTR_DISABLE, GPIO_PIN_INTR_POSEDGE, GPIO_PIN_INTR_NEGEDGE,
     GPIO_PIN_INTR_ANYEDGE, GPIO_PIN_INTR_LOLEVEL, GPIO_PIN_INTR_HILEVEL
     };
-  int type = opts_type[luaL_checkoption(L, 2, "", opts)];
-
   luaL_argcheck(L, platform_gpio_exists(pin) && pin>0, 1, "Invalid interrupt pin");
+  int type = opts_type[luaL_checkoption(L, 2, "none", opts)];
 
   if (type != GPIO_PIN_INTR_DISABLE) {
     int cbtype = lua_type(L, 3);
-    luaL_argcheck(L, cbtype == LUA_TFUNCTION || cbtype == LUA_TLIGHTFUNCTION, 3,
+    luaL_argcheck(L,  cbtype == LUA_TFUNCTION || cbtype == LUA_TLIGHTFUNCTION, 3,
       "invalid callback type");
     lua_pushvalue(L, 3);  // copy argument (func) to the top of stack
     gpio_cb_ref[pin] = luaL_ref(L, LUA_REGISTRYINDEX);
+  } else {
+    gpio_cb_ref[pin] = LUA_NOREF;
   }
+
+  if(old_pin_ref != LUA_NOREF) luaL_unref(L, LUA_REGISTRYINDEX, old_pin_ref);
+
   NODE_DBG("Pin data: %d %d %08x, %d %d %d, %08x\n",
           pin, type, pin_mux[pin], pin_num[pin], pin_func[pin], pin_int_type[pin], gpio_cb_ref[pin]);
   platform_gpio_intr_init(pin, type);

docs/en/modules/gpio.md

@@ -98,18 +98,18 @@ gpio.serout(1,1,{8,18},8) -- serial 30% pwm 38k, lasts 8 cycles
 
 ## gpio.trig()
 
-Establish a callback function to run on interrupt for a pin.
-
-There is currently no support for unregistering the callback.
+Establish or clear a callback function to run on interrupt for a pin.
 
 This function is not available if GPIO_INTERRUPT_ENABLE was undefined at compile time.
 
 #### Syntax
-`gpio.trig(pin, type [, function(level)])`
+`gpio.trig(pin, [type [, function(level)]})`
 
 #### Parameters
 - `pin` **1~12**, IO index, pin D0 does not support interrupt.
-- `type` "up", "down", "both", "low", "high", which represent rising edge, falling edge, both edge, low level, high level trig mode correspondingly.
+- `type` "up", "down", "both", "low", "high", which represent rising edge, falling edge, both edge, 
+low level, high level trig mode correspondingly. If the type is "none" or omitted then the
+callback function is removed and the interrupt disabled.
 - `function(level)` callback function when triggered. The gpio level is the param. Use previous callback function if undefined here.
 
 #### Returns
@@ -131,6 +131,9 @@ function pin1cb(level)
 end
 gpio.trig(pin, "down", pin1cb)
 
+```
+```Lua
+gpio.trig(4, 'none') -- remove any existing trigger
 ```
 #### See also
 [`gpio.mode()`](#gpiomode)