Support eeprom update notification. (#499)

Adds a weak callback to the eepromemulation driver, triggered
after each write is completed.

Shows with an example how to use this to automatically apply changes
that happened from JMRI configuration UI.

applications/io_board/targets/freertos.armv7m.ek-tm4c123gxl/main.cxx

@@ -127,6 +127,40 @@ openlcb::ConfiguredProducer producer_sw2(
 openlcb::RefreshLoop loop(
     stack.node(), {producer_sw1.polling(), producer_sw2.polling()});
 
+/// This timer checks the eeprom once a second and if the user has written
+/// something, executes a reload of the configuration via the OpenLCB config
+/// service.
+class AutoUpdateTimer : public ::Timer
+{
+public:
+    AutoUpdateTimer()
+        : ::Timer(stack.executor()->active_timers())
+    {
+        start(SEC_TO_NSEC(1));
+    }
+
+    long long timeout() override
+    {
+        extern uint8_t eeprom_updated;
+        if (eeprom_updated)
+        {
+            needUpdate_ = true;
+            eeprom_updated = 0;
+        }
+        else
+        {
+            if (needUpdate_)
+            {
+                stack.config_service()->trigger_update();
+                needUpdate_ = false;
+            }
+        }
+        return RESTART;
+    }
+
+    bool needUpdate_ {false};
+} update_timer;
+
 /** Entry point to application.
  * @param argc number of command line arguments
  * @param argv array of command line arguments

boards/ti-ek-tm4c123gxl-launchpad/HwInit.cxx

@@ -110,6 +110,15 @@ StoredBitSet* g_gpio_stored_bit_set = nullptr;
 constexpr unsigned EEPROM_BIT_COUNT = 84;
 constexpr unsigned EEPROM_BITS_PER_CELL = 28;
 
+/// This variable will be set to 1 when a write arrives to the eeprom.
+uint8_t eeprom_updated = 0;
+
+// Overridesthe default behavior to keep track of eeprom writes.
+void EEPROMEmulation::updated_notification()
+{
+    eeprom_updated = 1;
+}
+
 extern "C" {
 void hw_set_to_safe(void);
 

src/freertos_drivers/common/EEPROMEmulation.cxx

@@ -194,6 +194,8 @@ void EEPROMEmulation::write(unsigned int index, const void *buf, size_t len)
     {
         memcpy(shadow_ + shadow_index, shadow_data, shadow_len);
     }
+
+    updated_notification();
 }
 
 /** Write to the EEPROM on a native block boundary.

src/freertos_drivers/common/EEPROMEmulation.hxx

@@ -154,6 +154,12 @@ protected:
     static const size_t BLOCK_SIZE;
 
 private:
+    /** This function will be called after every write. The default
+     * implementation is a weak symbol with an empty function. It is intended
+     * to be overridden in the application to get callbacks for eeprom writes
+     * that can trigger a reload. */
+    void updated_notification();
+
     /** Write to the EEPROM.  NOTE!!! This is not necessarily atomic across
      * byte boundaries in the case of power loss.  The user should take this
      * into account as it relates to data integrity of a whole block.

src/freertos_drivers/common/EEPROMEmulation_weak.cxx

@@ -37,3 +37,11 @@
 // emulation implementation to prevent GCC from mistakenly optimizing away the
 // constant into a linker reference.
 const bool __attribute__((weak)) EEPROMEmulation::SHADOW_IN_RAM = false;
+
+/// This function will be called after every write. The default
+/// implementation is a weak symbol with an empty function. It is intended
+/// to be overridden in the application to get callbacks for eeprom writes
+/// that can trigger a reload.
+void __attribute__((weak)) EEPROMEmulation::updated_notification()
+{
+}