light: fix out-of-bounds access when using GPIO16

As noticed in the xoseperez#2472

Internal implemementation still lacks the support for the GPIO16,
as it needs to use 'special' IO16 registers (and due to the fact that the 'normal'
registers only fit in an u16[16], from 0 to 15, so internals need to change as well)
One possible way is to attach certain implementation funcs to the
struct handling the isr, avoiding a bunch of in-line checks for `pin == 16`

Another option is to just use Core's `analogWrite`, which hides the
implementation from us and should work pretty seamlessly.
(...but, currently has 2 different waveform generator types, and it is
not really clear which one is a better default, as it needs to be set at
build-time)

code/espurna/compat.h

@@ -121,6 +121,11 @@ constexpr const T& clamp(const T& value, const T& low, const T& high) {
     return (value < low) ? low : (high < value) ? high : value;
 }
 
+template <typename T, size_t Size>
+constexpr size_t size(const T (&)[Size]) {
+    return Size;
+}
+
 } // namespace std
 
 #endif

code/espurna/light.cpp

@@ -2906,20 +2906,24 @@ void lightTransition(LightTransition transition) {
 namespace {
 
 #if LIGHT_PROVIDER == LIGHT_PROVIDER_DIMMER
-const unsigned long _light_iomux[16] PROGMEM = {
+const unsigned long _light_iomux[] PROGMEM = {
     PERIPHS_IO_MUX_GPIO0_U, PERIPHS_IO_MUX_U0TXD_U, PERIPHS_IO_MUX_GPIO2_U, PERIPHS_IO_MUX_U0RXD_U,
     PERIPHS_IO_MUX_GPIO4_U, PERIPHS_IO_MUX_GPIO5_U, PERIPHS_IO_MUX_SD_CLK_U, PERIPHS_IO_MUX_SD_DATA0_U,
     PERIPHS_IO_MUX_SD_DATA1_U, PERIPHS_IO_MUX_SD_DATA2_U, PERIPHS_IO_MUX_SD_DATA3_U, PERIPHS_IO_MUX_SD_CMD_U,
     PERIPHS_IO_MUX_MTDI_U, PERIPHS_IO_MUX_MTCK_U, PERIPHS_IO_MUX_MTMS_U, PERIPHS_IO_MUX_MTDO_U
 };
 
-const unsigned long _light_iofunc[16] PROGMEM = {
+const unsigned long _light_iofunc[] PROGMEM = {
     FUNC_GPIO0, FUNC_GPIO1, FUNC_GPIO2, FUNC_GPIO3,
     FUNC_GPIO4, FUNC_GPIO5, FUNC_GPIO6, FUNC_GPIO7,
     FUNC_GPIO8, FUNC_GPIO9, FUNC_GPIO10, FUNC_GPIO11,
     FUNC_GPIO12, FUNC_GPIO13, FUNC_GPIO14, FUNC_GPIO15
 };
 
+bool _lightIoMuxPin(unsigned char pin) {
+    return (pin < std::size(_light_iofunc)) && (pin < std::size(_light_iomux));
+}
+
 #endif
 
 inline bool _lightUseGamma(size_t channels, size_t index) {
@@ -3162,14 +3166,14 @@ void lightSetup() {
 
             // Load up until first GPIO_NONE. Allow settings to override, but not remove values
             const auto pin = Light::settings::channelPin(index);
-            if (!gpioValid(pin)) {
+            if (!gpioValid(pin) || !_lightIoMuxPin(pin)) {
                 break;
             }
 
             _light_channels.emplace_back(pin);
 
-            io_info[index][0] = pgm_read_dword(&_light_iomux[pin]);
-            io_info[index][1] = pgm_read_dword(&_light_iofunc[pin]);
+            io_info[index][0] = _light_iomux[pin];
+            io_info[index][1] = _light_iofunc[pin];
             io_info[index][2] = pin;
             pinMode(pin, OUTPUT);