Initialise EEPROM and save periodically

This should be less of a disaster for the emulated
EEPROM on the pico, but could use some finesse

src/main.cpp

@@ -20,6 +20,11 @@
 #include <Arduino.h>
 #include <stdint.h>
 #include <ComPort.h>
+#ifdef SUPPORT_EEPROM
+#include <EEPROM.h>
+#else
+#include "dummyEEPROM.h"
+#endif
 
 #ifdef HELP
     #include "modules/help/help.h"
@@ -54,6 +59,7 @@ uint8_t registered_loop_fn_count = 0;
 const Command core_commands[] = {
     {"version", get_version},
     {"list_modules", get_modules},
+    {"eeprom_last_commit", get_eeprom_last_commit},
     END_COMMAND};
 
 void register_module(const Command commands[], void (*loop_fn)(void))
@@ -135,8 +141,42 @@ void get_modules(String)
     comPort->println("--END--");
 }
 
+#if defined(SUPPORT_EEPROM) && defined(MCU_PICO)
+unsigned long eeprom_last_commit;
+void eeprom_commit_at_interval(unsigned long interval)
+{
+    unsigned long next_commit = eeprom_last_commit + interval;
+    unsigned long now = millis();
+    // millis() can overflow - this if statement will trigger
+    // every `interval` accounting for overflows.
+    if ( (now > next_commit && next_commit > eeprom_last_commit) // no overflow
+         || (now > next_commit && now < eeprom_last_commit)) // overflow
+    {
+        EEPROM.commit();
+        eeprom_last_commit = millis();
+    }
+}
+#endif
+
+void get_eeprom_last_commit(String)
+{
+#if defined(SUPPORT_EEPROM) && defined(MCU_PICO)
+    comPort->println(eeprom_last_commit);
+#else
+    comPort->println("Not using pico");
+#endif
+    return;
+}
+
 void setup()
 {
+    #if defined(SUPPORT_EEPROM) && defined(MCU_PICO)
+        // On the Pico, EEPROM is emulated.
+        // This means we need to explicitly enable it, and also 
+        // call EEPROM.commit() periodically to persist it to flash.
+        EEPROM.begin(256);
+        eeprom_last_commit = millis();
+    #endif
     // initialise serial port
     #ifdef WIRING_SERIAL_TX
         Serial2.setTX(WIRING_SERIAL_TX);
@@ -186,17 +226,26 @@ void setup()
 
 void loop()
 {
+    bool bytesAvailable = false;
     if (PRIMARY_SERIAL_PORT.available())
     {
         comPort = (HardwareSerial*) &PRIMARY_SERIAL_PORT;
-        handle_command(comPort->readStringUntil('\n'));
+        bytesAvailable = true;
     }
     #if defined(SECONDARY_SERIAL_PORT)
-    if (SECONDARY_SERIAL_PORT.available())
+    else if (SECONDARY_SERIAL_PORT.available())
     {
         comPort = (HardwareSerial*) &SECONDARY_SERIAL_PORT;
+        bytesAvailable = true;
+    }
+    if (bytesAvailable)
+    {
         handle_command(comPort->readStringUntil('\n'));
     }
+    #if defined(SUPPORT_EEPROM) && defined(MCU_PICO)
+    // On the Pico, emulated EEPROM is only saved to flash when we call commit()
+    eeprom_commit_at_interval(10000); // NB this only writes to flash if something has changed.
+    #endif
 
     for (int i = 0; i < registered_loop_fn_count; i++)
         registered_loop_functions[i]();

src/main.h

@@ -29,5 +29,6 @@ extern void register_module(const Command commands[], void (*loop_fn)(void));
 
 void get_version(String);
 void get_modules(String);
+void get_eeprom_last_commit(String);
 #define MAIN_H
 #endif