Split Nano firmware into modules

- config.h: all constants and debug defines
- command_parser.h/.cpp: CommandParser class, one method per command
- settings.h/.cpp: EEPROM flip time storage
- main.cpp: setup/loop and the periodic full redraw only
- Full redraw now checks frameEnded() after the serial buffer is drained
- Drop the SPI/Adafruit_I2CDevice include workaround (not needed)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -42,6 +42,8 @@ See README.md for the overview.
 
 ## Nano serial parser (`src/nano/main.cpp`)
 
+- Files: `main.cpp` (setup/loop, refresh), `config.h` (all constants and debug
+  defines), `command_parser.*` (protocol, one method per command), `settings.*` (EEPROM).
 - Line based and non-blocking: bytes are collected into a 64-character buffer and a
   command runs when `\n` arrives. Bitmap (`B`) pixel data is the exception. It is drawn
   while it arrives, so it can be longer than the buffer. Keep `loop()` free of busy-waits.
@@ -53,7 +55,7 @@ See README.md for the overview.
 - The Nano only replies `READY` (at boot) and `ERR: ...`. There is no per-frame
   acknowledgement. Whether the Nano's TX is wired to the ESP's RX is unconfirmed, so every
   wait for a reply needs a timeout.
-- To test the parser without hardware, compile `main.cpp` with g++ (Strawberry Perl
+- To test the parser without hardware, compile all `src/nano/*.cpp` files with g++ (Strawberry Perl
   provides it at `C:\Strawberry\c\bin`) and mock headers for `Arduino.h`, `EEPROM.h` and
   `BROSE9323.h`.
 

src/nano/README.md

@@ -6,6 +6,17 @@ The Nano is connected directly to the Brose panel electronics. It keeps an 84 ×
 buffer and takes drawing commands over serial (115200 baud). It has no clock or network
 logic.
 
+## Files
+
+| File | Contents |
+|------|----------|
+| `main.cpp` | `setup()` / `loop()`, feeds serial bytes to the parser, periodic full redraw |
+| `config.h` | All settings: debug options, display size, flip time limits, timings |
+| `command_parser.h/.cpp` | `CommandParser`: the serial protocol, one method per command |
+| `settings.h/.cpp` | Flip time stored in EEPROM |
+
+The display driver itself is in [lib/BROSE9323](../../lib/BROSE9323/README.md).
+
 ## Behaviour
 
 - **Boot:** the Nano loads the flip time from EEPROM, sets up the pins and sends `READY`.
@@ -24,7 +35,7 @@ logic.
 
 ### Debug options
 
-Uncomment these at the top of `main.cpp`:
+Uncomment these in `config.h`:
 
 | Define | Effect |
 |--------|--------|

src/nano/command_parser.cpp

@@ -0,0 +1,258 @@
+#include "command_parser.h"
+
+#include "settings.h"
+
+// ---------------------------------------------------------------------------
+// Hex helpers
+// ---------------------------------------------------------------------------
+
+static bool isHex(char c)
+{
+	return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
+}
+
+static uint8_t hex2dec(char c)
+{
+	if (c >= '0' && c <= '9')
+		return c - '0';
+	if (c >= 'A' && c <= 'F')
+		return c - 'A' + 10;
+	if (c >= 'a' && c <= 'f')
+		return c - 'a' + 10;
+	return 0;
+}
+
+static uint8_t hex2byte(const char *s)
+{
+	return (hex2dec(s[0]) << 4) | hex2dec(s[1]);
+}
+
+static bool isBitmapCommand(char c)
+{
+	return c == 'b' || c == 'B';
+}
+
+// Length of a bitmap header: BxxyywwhhC
+static const uint8_t BITMAP_HEADER_LEN = 10;
+
+// ---------------------------------------------------------------------------
+// Input handling
+// ---------------------------------------------------------------------------
+
+CommandParser::CommandParser(BROSE9323 &display, Print &reply) : _display(display), _reply(reply)
+{
+}
+
+void CommandParser::feed(char c)
+{
+	if (_bitmap_active)
+	{
+		if (c == '\n')
+			_bitmap_active = false;
+		else
+			_bitmapData(c);
+		return;
+	}
+
+	if (c == '\n')
+	{
+		if (!_discard_line)
+			_runLine();
+		_line_len = 0;
+		_discard_line = false;
+		return;
+	}
+	if (c == '\r' || _discard_line)
+		return;
+	if (_line_len >= LINE_MAX)
+	{
+		_error(F("Line too long"));
+		_discard_line = true;
+		return;
+	}
+	_line[_line_len++] = c;
+	_frame_ended = false;
+
+	// Bitmap header complete: draw the pixel data as it arrives
+	if (_line_len == BITMAP_HEADER_LEN && isBitmapCommand(_line[0]))
+	{
+		_line_len = 0;
+		if (!_bitmapStart())
+			_discard_line = true;
+	}
+}
+
+bool CommandParser::frameEnded() const
+{
+	return _frame_ended;
+}
+
+// Run one complete command line (without the '\n')
+void CommandParser::_runLine()
+{
+	if (_line_len == 0)
+		return;
+	_line[_line_len] = '\0';
+
+	char cmd = _line[0];
+	switch (cmd)
+	{
+	case 'b':
+	case 'B':
+		// Complete bitmap headers are handled in feed()
+		_error(F("Incomplete bitmap header"));
+		break;
+	case 'd':
+	case 'D':
+		_display.display();
+		_frame_ended = true;
+		break;
+	case 'f':
+	case 'F':
+		_fill();
+		break;
+	case 'p':
+	case 'P':
+		_print();
+		break;
+	case 'r':
+	case 'R':
+		_display.printBuffer();
+		_reply.flush();
+		break;
+	case 's':
+	case 'S':
+		_pixel(cmd == 'S');
+		break;
+	case 't':
+	case 'T':
+		_timing();
+		break;
+	default:
+#ifdef DEBUG
+		_reply.print(F("0x"));
+		_reply.print(cmd >> 4, HEX);
+		_reply.print(cmd & 0xF, HEX);
+		_reply.println(F(" - command not known."));
+#endif
+		break;
+	}
+}
+
+void CommandParser::_error(const __FlashStringHelper *msg)
+{
+	_reply.print(F("ERR: "));
+	_reply.println(msg);
+}
+
+// ---------------------------------------------------------------------------
+// Commands
+// ---------------------------------------------------------------------------
+
+// BxxyywwhhcBITMAP (xx/ww = 8 bit hex x position/width; yy/hh = 8 bit hex y position/height;
+// c = 0/1 color; BITMAP = one hex digit per 4 pixels, row by row, width must be a multiple of 4)
+bool CommandParser::_bitmapStart()
+{
+	_bitmap_x = hex2byte(_line + 1);
+	_bitmap_y = hex2byte(_line + 3);
+	_bitmap_w = hex2byte(_line + 5);
+	_bitmap_h = hex2byte(_line + 7);
+	_bitmap_color = _line[9] != '0';
+	if (_bitmap_w == 0 || _bitmap_w % 4)
+	{
+		_error(F("Invalid bitmap width (not dividable by 4)"));
+		return false;
+	}
+	if (_bitmap_h == 0)
+	{
+		_error(F("Invalid bitmap height (0)"));
+		return false;
+	}
+	_bitmap_nibble = 0;
+	_bitmap_active = true;
+	return true;
+}
+
+void CommandParser::_bitmapData(char c)
+{
+	if (!isHex(c))
+		return;
+	uint16_t pixel = _bitmap_nibble * 4;
+	if (pixel >= (uint16_t)_bitmap_w * _bitmap_h)
+		return; // more data than the bitmap size, ignore
+	uint8_t b = hex2dec(c);
+	for (uint8_t i = 0; i < 4; i++)
+	{
+		if (b & (0x8 >> i))
+		{
+			uint16_t p = pixel + i;
+			_display.drawPixel(_bitmap_x + p % _bitmap_w, _bitmap_y + p / _bitmap_w, _bitmap_color);
+		}
+	}
+	_bitmap_nibble++;
+}
+
+// Fc (c = 0/1 color)
+void CommandParser::_fill()
+{
+	if (_line_len < 2)
+	{
+		_error(F("Missing color"));
+		return;
+	}
+	_display.fillScreen(_line[1] != '0');
+}
+
+// PxxyycsTEXT (xx = 8 bit hex x position; yy = 8 bit hex y position; c = 0/1 color;
+// s = 1-9 size; TEXT = string, newline = escaped \n)
+void CommandParser::_print()
+{
+	if (_line_len < 7)
+	{
+		_error(F("Incomplete print command"));
+		return;
+	}
+	bool color = _line[5] != '0';
+	_display.setCursor(hex2byte(_line + 1), hex2byte(_line + 3));
+	_display.setTextColor(color, !color);
+	_display.setTextSize(_line[6] - '0');
+	for (uint8_t i = 7; i < _line_len; i++)
+	{
+		if (_line[i] == '\\' && _line[i + 1] == 'n')
+		{
+			_display.println();
+			i++;
+		}
+		else
+		{
+			_display.write(_line[i]);
+		}
+	}
+}
+
+// sxxyyc / Sxxyyc (xx = 8 bit hex x position; yy = 8 bit hex y position; c = 0/1 color)
+// s only changes the buffer, S flips the dot immediately
+void CommandParser::_pixel(bool direct)
+{
+	if (_line_len < 6)
+	{
+		_error(F("Incomplete pixel command"));
+		return;
+	}
+	_display.setDirect(direct);
+	_display.drawPixel(hex2byte(_line + 1), hex2byte(_line + 3), hex2dec(_line[5]));
+	_display.setDirect(false);
+}
+
+// Tttt (ttt = decimal flip time in us), stored in EEPROM
+void CommandParser::_timing()
+{
+	long t = atol(_line + 1);
+	if (t < FLIP_TIME_MIN || t > FLIP_TIME_MAX)
+	{
+		_error(F("Flip time out of range (50-2000 us)"));
+		return;
+	}
+	_display.setTiming(t);
+	saveFlipTime(t);
+}

src/nano/command_parser.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <Arduino.h>
+
+#include "BROSE9323.h"
+#include "config.h"
+
+// Parses the line based serial protocol from the ESP32 (see README.md) and draws on the
+// display. Bytes are fed one by one; a command runs when its '\n' arrives, so nothing
+// here blocks while waiting for data.
+class CommandParser
+{
+public:
+	CommandParser(BROSE9323 &display, Print &reply);
+
+	// Handle one received byte
+	void feed(char c);
+
+	// True when the last command was D (end of a frame) and no new command has started
+	bool frameEnded() const;
+
+private:
+	BROSE9323 &_display;
+	Print &_reply;
+
+	char _line[LINE_MAX + 1];
+	uint8_t _line_len = 0;
+	bool _discard_line = false; // skip everything until the next '\n'
+	bool _frame_ended = false;
+
+	// Bitmap (B) pixel data is drawn while it arrives instead of being buffered
+	bool _bitmap_active = false;
+	uint8_t _bitmap_x, _bitmap_y, _bitmap_w, _bitmap_h;
+	bool _bitmap_color;
+	uint16_t _bitmap_nibble;
+
+	void _runLine();
+	void _error(const __FlashStringHelper *msg);
+
+	// Commands
+	bool _bitmapStart();
+	void _bitmapData(char c);
+	void _fill();
+	void _print();
+	void _pixel(bool direct);
+	void _timing();
+};

src/nano/config.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <Arduino.h>
+
+// ---------------------------------------------------------------------------
+// Debug options (uncomment to enable)
+// ---------------------------------------------------------------------------
+
+// Print unknown command bytes on the serial port
+//#define DEBUG
+
+// Time a full redraw at boot and print the duration in ms
+//#define MEASURE_REFRESH
+
+// ---------------------------------------------------------------------------
+// Display
+// ---------------------------------------------------------------------------
+
+// Three Brose panels of 28 x 19 next to each other
+const uint8_t DISPLAY_WIDTH = 84;
+const uint8_t DISPLAY_HEIGHT = 19;
+const uint8_t PANEL_WIDTH = 28;
+
+// Flip pulse length in us, stored in EEPROM and changed with the T command
+const uint16_t FLIP_TIME_DEFAULT = 200;
+const uint16_t FLIP_TIME_MIN = 50;
+const uint16_t FLIP_TIME_MAX = 2000;
+
+// Full redraw interval, fixes dots that did not flip
+const uint32_t REFRESH_TIME = 120000UL; // 2 min
+
+// ---------------------------------------------------------------------------
+// Serial link to the ESP32
+// ---------------------------------------------------------------------------
+
+const uint32_t SERIAL_BAUD = 115200;
+
+// Serial line quiet for this long: safe to do a due full redraw without waiting for a D
+const uint32_t IDLE_TIME = 2000UL;
+
+// Longest command line (bitmap data is streamed and does not count)
+const uint8_t LINE_MAX = 64;

src/nano/main.cpp

@@ -1,257 +1,35 @@
+// Arduino Nano firmware: drives the Brose flipdot panels and draws what the ESP32 sends
+// over serial. See README.md for the protocol and wiring.
+
 #include <Arduino.h>
+
 #include "BROSE9323.h"
-// fixes
-#include <SPI.h>
-#include <Adafruit_I2CDevice.h>
+#include "command_parser.h"
+#include "config.h"
+#include "settings.h"
 
-#include <EEPROM.h>
-
-//#define DEBUG
-// Print how long a full redraw takes (in ms) at startup
-//#define MEASURE_REFRESH
-
-// Flip pulse length in us, stored in EEPROM and changed with the T command
-const uint16_t FLIP_TIME_DEFAULT = 200;
-const uint16_t FLIP_TIME_MIN = 50;
-const uint16_t FLIP_TIME_MAX = 2000;
-
-// EEPROM layout: magic marker (marks the stored value as valid), then the flip time
-const int EEPROM_MAGIC_ADDR = 0;
-const int EEPROM_FLIP_TIME_ADDR = 2;
-const uint16_t EEPROM_MAGIC = 0xF11D;
-
-// Full redraw interval, fixes dots that did not flip
-const uint32_t REFRESH_TIME = 120000UL; // 2 min
-// Serial line quiet for this long: safe to do a due full redraw without waiting for a D
-const uint32_t IDLE_TIME = 2000UL;
-
-// Longest command line (bitmap data is streamed and does not count)
-const uint8_t LINE_MAX = 64;
-
-BROSE9323 display(84, 19, 28, FLIP_TIME_DEFAULT);
-
-char line[LINE_MAX + 1];
-uint8_t line_len = 0;
-bool discard_line = false; // skip everything until the next '\n'
-
-// Bitmap (B) pixel data is drawn while it arrives instead of being buffered
-bool bitmap_active = false;
-uint8_t bitmap_x, bitmap_y, bitmap_w, bitmap_h;
-bool bitmap_color;
-uint16_t bitmap_nibble;
+BROSE9323 display(DISPLAY_WIDTH, DISPLAY_HEIGHT, PANEL_WIDTH, FLIP_TIME_DEFAULT);
+CommandParser parser(display, Serial);
 
 uint32_t last_refresh;
 uint32_t last_rx;
 
-uint8_t hex2dec(char c)
-{
-	if (c >= '0' && c <= '9')
-		return c - '0';
-	if (c >= 'A' && c <= 'F')
-		return c - 'A' + 10;
-	if (c >= 'a' && c <= 'f')
-		return c - 'a' + 10;
-	return 0;
-}
-
-bool isHex(char c)
-{
-	return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
-}
-
-uint8_t hex2byte(const char *s)
-{
-	return (hex2dec(s[0]) << 4) | hex2dec(s[1]);
-}
-
-void printError(const __FlashStringHelper *msg)
-{
-	Serial.print(F("ERR: "));
-	Serial.println(msg);
-}
-
-uint16_t loadFlipTime()
-{
-	uint16_t magic, t;
-	EEPROM.get(EEPROM_MAGIC_ADDR, magic);
-	EEPROM.get(EEPROM_FLIP_TIME_ADDR, t);
-	if (magic != EEPROM_MAGIC || t < FLIP_TIME_MIN || t > FLIP_TIME_MAX)
-		return FLIP_TIME_DEFAULT;
-	return t;
-}
-
-void saveFlipTime(uint16_t t)
-{
-	// put() only writes bytes that changed
-	EEPROM.put(EEPROM_FLIP_TIME_ADDR, t);
-	EEPROM.put(EEPROM_MAGIC_ADDR, EEPROM_MAGIC);
-}
-
-// Force a full redraw every REFRESH_TIME. Only called when no data is expected,
-// because the redraw blocks long enough to overflow the 64 byte serial buffer.
+// Force a full redraw every REFRESH_TIME. The redraw blocks long enough to overflow the
+// 64 byte serial buffer, so it only runs when no data is expected: right after the ESP
+// finished a frame, or when the serial line is idle.
 void refreshIfDue()
 {
-	if (millis() - last_refresh >= REFRESH_TIME)
+	bool quiet = parser.frameEnded() || millis() - last_rx >= IDLE_TIME;
+	if (quiet && millis() - last_refresh >= REFRESH_TIME)
 	{
 		display.display(true);
 		last_refresh = millis();
 	}
 }
 
-// BxxyywwhhcBITMAP (xx/ww = 8 bit hex x position/width; yy/hh = 8 bit hex y position/height;
-// c = 0/1 color; BITMAP = one hex digit per 4 pixels, row by row, width must be a multiple of 4)
-bool startBitmap()
-{
-	bitmap_x = hex2byte(line + 1);
-	bitmap_y = hex2byte(line + 3);
-	bitmap_w = hex2byte(line + 5);
-	bitmap_h = hex2byte(line + 7);
-	bitmap_color = line[9] != '0';
-	if (bitmap_w == 0 || bitmap_w % 4)
-	{
-		printError(F("Invalid bitmap width (not dividable by 4)"));
-		return false;
-	}
-	if (bitmap_h == 0)
-	{
-		printError(F("Invalid bitmap height (0)"));
-		return false;
-	}
-	bitmap_nibble = 0;
-	bitmap_active = true;
-	return true;
-}
-
-void bitmapData(char c)
-{
-	if (!isHex(c))
-		return;
-	uint16_t pixel = bitmap_nibble * 4;
-	if (pixel >= (uint16_t)bitmap_w * bitmap_h)
-		return; // more data than the bitmap size, ignore
-	uint8_t b = hex2dec(c);
-	for (uint8_t i = 0; i < 4; i++)
-	{
-		if (b & (0x8 >> i))
-		{
-			uint16_t p = pixel + i;
-			display.drawPixel(bitmap_x + p % bitmap_w, bitmap_y + p / bitmap_w, bitmap_color);
-		}
-	}
-	bitmap_nibble++;
-}
-
-// Handle one complete command line (without the '\n')
-void processLine()
-{
-	if (line_len == 0)
-		return;
-	line[line_len] = '\0';
-
-	char cmd = line[0];
-	switch (cmd)
-	{
-	// Bitmap header shorter than 10 characters (complete headers are handled in loop())
-	case 'b':
-	case 'B':
-		printError(F("Incomplete bitmap header"));
-		break;
-	// Display
-	case 'd':
-	case 'D': // D
-		display.display();
-		// The ESP sends D at the end of a frame, so the line is quiet now
-		refreshIfDue();
-		break;
-	// Fill Screen
-	case 'f':
-	case 'F': // Fc (c = 0/1 color)
-		if (line_len < 2)
-		{
-			printError(F("Missing color"));
-			break;
-		}
-		display.fillScreen(line[1] != '0');
-		break;
-	// Print Text
-	case 'p':
-	case 'P': // PxxyycsTEXT (xx = 8 bit hex x position; yy = 8 bit hex y position; c = 0/1 color; s = 1-9 size; TEXT = string, newline = escaped \n)
-	{
-		if (line_len < 7)
-		{
-			printError(F("Incomplete print command"));
-			break;
-		}
-		bool color = line[5] != '0';
-		display.setCursor(hex2byte(line + 1), hex2byte(line + 3));
-		display.setTextColor(color, !color);
-		display.setTextSize(line[6] - '0');
-		for (uint8_t i = 7; i < line_len; i++)
-		{
-			if (line[i] == '\\' && line[i + 1] == 'n')
-			{
-				display.println();
-				i++;
-			}
-			else
-			{
-				display.write(line[i]);
-			}
-		}
-		break;
-	}
-	// Return buffer (show pixels on console)
-	case 'r':
-	case 'R': // R
-		display.printBuffer();
-		Serial.flush();
-		break;
-	// Set Pixel (S = flip immediately, s = buffer only)
-	case 'S':
-	case 's': // Sxxyyc (xx = 8 bit hex x position; yy = 8 bit hex y position; c = 0/1 color)
-		if (line_len < 6)
-		{
-			printError(F("Incomplete pixel command"));
-			break;
-		}
-		display.setDirect(cmd == 'S');
-		display.drawPixel(hex2byte(line + 1), hex2byte(line + 3), hex2dec(line[5]));
-		display.setDirect(false);
-		break;
-	// Set Timing
-	case 'T':
-	case 't': // Tttt (ttt = decimal flip time in us)
-	{
-		long t = atol(line + 1);
-		if (t < FLIP_TIME_MIN || t > FLIP_TIME_MAX)
-		{
-			printError(F("Flip time out of range (50-2000 us)"));
-			break;
-		}
-		display.setTiming(t);
-		saveFlipTime(t);
-		break;
-	}
-	default:
-#ifdef DEBUG
-		Serial.print("0x");
-		Serial.print(cmd >> 4, HEX);
-		Serial.print(cmd & 0xF, HEX);
-		Serial.println(" - command not known.");
-		Serial.flush();
-#endif
-		break;
-	}
-}
-
-void setup()
-{
-	Serial.begin(115200);
-
-	display.setTiming(loadFlipTime());
-	display.begin();
-
 #ifdef MEASURE_REFRESH
+void measureRefresh()
+{
 	delay(1000);
 
 	display.fillScreen(1);
@@ -261,6 +39,18 @@ void setup()
 	display.display();
 	uint32_t t2 = millis();
 	Serial.println(t2 - t1);
+}
+#endif
+
+void setup()
+{
+	Serial.begin(SERIAL_BAUD);
+
+	display.setTiming(loadFlipTime());
+	display.begin();
+
+#ifdef MEASURE_REFRESH
+	measureRefresh();
 #endif
 
 	last_refresh = millis();
@@ -274,46 +64,9 @@ void loop()
 {
 	while (Serial.available())
 	{
-		char c = Serial.read();
 		last_rx = millis();
-
-		if (bitmap_active)
-		{
-			if (c == '\n')
-				bitmap_active = false;
-			else
-				bitmapData(c);
-			continue;
-		}
-
-		if (c == '\n')
-		{
-			if (!discard_line)
-				processLine();
-			line_len = 0;
-			discard_line = false;
-			continue;
-		}
-		if (c == '\r' || discard_line)
-			continue;
-		if (line_len >= LINE_MAX)
-		{
-			printError(F("Line too long"));
-			discard_line = true;
-			continue;
-		}
-		line[line_len++] = c;
-
-		// Bitmap header complete: draw the pixel data as it arrives
-		if (line_len == 10 && (line[0] == 'b' || line[0] == 'B'))
-		{
-			line_len = 0;
-			if (!startBitmap())
-				discard_line = true;
-		}
+		parser.feed(Serial.read());
 	}
 
-	// No frames coming in (e.g. ESP idle): do the full redraw now if it is due
-	if (millis() - last_rx >= IDLE_TIME)
-		refreshIfDue();
+	refreshIfDue();
 }

src/nano/settings.cpp

@@ -0,0 +1,27 @@
+#include "settings.h"
+
+#include <EEPROM.h>
+
+#include "config.h"
+
+// EEPROM layout: magic marker (marks the stored value as valid), then the flip time
+const int EEPROM_MAGIC_ADDR = 0;
+const int EEPROM_FLIP_TIME_ADDR = 2;
+const uint16_t EEPROM_MAGIC = 0xF11D;
+
+uint16_t loadFlipTime()
+{
+	uint16_t magic, t;
+	EEPROM.get(EEPROM_MAGIC_ADDR, magic);
+	EEPROM.get(EEPROM_FLIP_TIME_ADDR, t);
+	if (magic != EEPROM_MAGIC || t < FLIP_TIME_MIN || t > FLIP_TIME_MAX)
+		return FLIP_TIME_DEFAULT;
+	return t;
+}
+
+void saveFlipTime(uint16_t t)
+{
+	// put() only writes bytes that changed
+	EEPROM.put(EEPROM_FLIP_TIME_ADDR, t);
+	EEPROM.put(EEPROM_MAGIC_ADDR, EEPROM_MAGIC);
+}

src/nano/settings.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <Arduino.h>
+
+// Settings that survive a power cycle (stored in EEPROM)
+
+// Stored flip time, or FLIP_TIME_DEFAULT when nothing valid is stored
+uint16_t loadFlipTime();
+
+void saveFlipTime(uint16_t t);