Add EEPROM retain menu option

Closes #139

README.md

@@ -11,6 +11,7 @@ If you're into "generic" AVR programming, I'm happy to tell you that all relevan
 * [Supported clock frequencies](#supported-clock-frequencies)
 * [Bootloader option](#bootloader-option)
 * [BOD option](#bod-option)
+* [EEPROM retain option](#eeprom-option)
 * [Link time optimization / LTO](#link-time-optimization--lto)
 * [Printf support](#printf-support)
 * [Pin macros](#pin-macros)
@@ -96,6 +97,10 @@ Brown out detection, or BOD for short lets the microcontroller sense the input v
 | Disabled  | Disabled  | Disabled | Disabled | Disabled |
 
 
+## EEPROM option
+If you want the EEPROM to be erased every time you burn the bootloader or upload using a programmer, you can turn off this option. You'll have to connect an ISP programmer and hit "Burn bootloader" to enable or disable EEPROM retain. Note that when uploading using a bootloader, the EEPROM will always be retained.
+
+
 ## Link time optimization / LTO
 After Arduino IDE 1.6.11 where released, There have been support for link time optimization or LTO for short. The LTO optimizes the code at link time, making the code (often) significantly smaller without making it "slower". In Arduino IDE 1.6.11 and newer LTO is enabled by default. I've chosen to disable this by default to make sure the core keep its backwards compatibility. Enabling LTO in IDE 1.6.10 or older will return an error. 
 I encourage you to try the new LTO option and see how much smaller your code gets! Note that you don't need to hit "Burn Bootloader" in order to enable LTO. Simply enable it in the "Tools" menu, and your code is ready for compilation. If you want to read more about LTO and GCC flags in general, head over to the [GNU GCC website](https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html)!
@@ -104,7 +109,7 @@ I encourage you to try the new LTO option and see how much smaller your code get
 ## Printf support
 Unlike the official Arduino cores, MiniCore has printf support out of the box. If you're not familiar with printf you should probably [read this first](https://www.tutorialspoint.com/c_standard_library/c_function_printf.htm). It's added to the Print class and will work with all libraries that inherit Print. Printf is a standard C function that lets you format text much easier than using Arduino's built-in print and println. Note that this implementation of printf will NOT print floats or doubles. This is a limitation of the avr-libc printf implementation on AVR microcontrollers, and nothing I can easily fix.
 
-If you're using a serial port, simply use `Serial.printf("Milliseconds since start: %ld\n", millis());`. Other libraries that inherit the Print class (and thus supports printf) are the LiquidCrystal LCD library and the U8G2 graphical LCD library.
+If you're using a serial port, simply use `Serial.printf("Milliseconds since start: %ld\n", millis());`. You can also use the `F()` macro if you need to store the string in flash. Other libraries that inherit the Print class (and thus supports printf) are the LiquidCrystal LCD library and the U8G2 graphical LCD library.
 
 
 ## Pin macros

avr/boards.txt

@@ -32,6 +32,7 @@
 # Menu options
 menu.clock=Clock
 menu.BOD=BOD
+menu.eeprom=EEPROM
 menu.LTO=Compiler LTO 
 menu.variant=Variant
 menu.bootloader=Bootloader
@@ -59,23 +60,29 @@ menu.bootloader=Bootloader
 328.menu.bootloader.uart0.upload.protocol=arduino
 328.menu.bootloader.uart0.upload.port=UART0
 328.menu.bootloader.uart0.build.export_merged_output=true
-328.menu.bootloader.uart0.bootloader.high_fuses=0xd6
+328.menu.bootloader.uart0.bootloader.high_fuses=0b1101{bootloader.eesave_bit}110
 328.menu.bootloader.uart0.bootloader.file=optiboot_flash/bootloaders/{build.mcu}/{build.clock_speed}/optiboot_flash_{build.mcu}_{upload.port}_{upload.speed}_{build.clock_speed}_{build.bootloader_led}.hex
 
 328.menu.bootloader.uart1=Yes (UART1 328PB only)
 328.menu.bootloader.uart1.upload.maximum_size=32256
 328.menu.bootloader.uart1.upload.protocol=arduino
 328.menu.bootloader.uart1.upload.port=UART1
 328.menu.bootloader.uart1.build.export_merged_output=true
-328.menu.bootloader.uart1.bootloader.high_fuses=0xd6
+328.menu.bootloader.uart1.bootloader.high_fuses=0b1101{bootloader.eesave_bit}110
 328.menu.bootloader.uart1.bootloader.file=optiboot_flash/bootloaders/{build.mcu}/{build.clock_speed}/optiboot_flash_{build.mcu}_{upload.port}_{upload.speed}_{build.clock_speed}_{build.bootloader_led}.hex
 
 328.menu.bootloader.no_bootloader=No bootloader
 328.menu.bootloader.no_bootloader.upload.maximum_size=32768
 328.menu.bootloader.no_bootloader.build.export_merged_output=false
-328.menu.bootloader.no_bootloader.bootloader.high_fuses=0xd7
+328.menu.bootloader.no_bootloader.bootloader.high_fuses=0b1101{bootloader.eesave_bit}111
 328.menu.bootloader.no_bootloader.bootloader.file=empty/empty.hex
 
+# EEPROM
+328.menu.eeprom.keep=EEPROM retained
+328.menu.eeprom.keep.bootloader.eesave_bit=0
+328.menu.eeprom.erase=EEPROM not retained
+328.menu.eeprom.erase.bootloader.eesave_bit=1
+
 # Variants
 328.menu.variant.modelP=328P / 328PA
 328.menu.variant.modelP.bootloader.cksel_bits=0111
@@ -271,6 +278,12 @@ menu.bootloader=Bootloader
 168.menu.bootloader.no_bootloader.bootloader.extended_fuses=0xfd
 168.menu.bootloader.no_bootloader.bootloader.file=empty/empty.hex
 
+# EEPROM
+168.menu.eeprom.keep=EEPROM retained
+168.menu.eeprom.keep.bootloader.eesave_bit=0
+168.menu.eeprom.erase=EEPROM not retained
+168.menu.eeprom.erase.bootloader.eesave_bit=1
+
 # Variants
 168.menu.variant.modelP=168P / 168PA
 168.menu.variant.modelP.bootloader.cksel_bits=0111
@@ -289,13 +302,13 @@ menu.bootloader=Bootloader
 
 # Brown out detection
 168.menu.BOD.2v7=BOD 2.7V
-168.menu.BOD.2v7.bootloader.high_fuses=0xd5
+168.menu.BOD.2v7.bootloader.high_fuses=0b1101{bootloader.eesave_bit}101
 168.menu.BOD.4v3=BOD 4.3V
-168.menu.BOD.4v3.bootloader.high_fuses=0xd4
+168.menu.BOD.4v3.bootloader.high_fuses=0b1101{bootloader.eesave_bit}100
 168.menu.BOD.1v8=BOD 1.8V
-168.menu.BOD.1v8.bootloader.high_fuses=0xd6
+168.menu.BOD.1v8.bootloader.high_fuses=0b1101{bootloader.eesave_bit}110
 168.menu.BOD.disabled=BOD disabled
-168.menu.BOD.disabled.bootloader.high_fuses=0xd7
+168.menu.BOD.disabled.bootloader.high_fuses=0b1101{bootloader.eesave_bit}111
 
 # Compiler link time optimization
 168.menu.LTO.Os=LTO Disabled
@@ -462,6 +475,12 @@ menu.bootloader=Bootloader
 88.menu.bootloader.no_bootloader.bootloader.extended_fuses=0xfd
 88.menu.bootloader.no_bootloader.bootloader.file=empty/empty.hex
 
+# EEPROM
+88.menu.eeprom.keep=EEPROM retained
+88.menu.eeprom.keep.bootloader.eesave_bit=0
+88.menu.eeprom.erase=EEPROM not retained
+88.menu.eeprom.erase.bootloader.eesave_bit=1
+
 # Variants
 88.menu.variant.modelP=88P / 88PA
 88.menu.variant.modelP.bootloader.cksel_bits=0111
@@ -480,13 +499,13 @@ menu.bootloader=Bootloader
 
 # Brown out detection
 88.menu.BOD.2v7=BOD 2.7V
-88.menu.BOD.2v7.bootloader.high_fuses=0xd5
+88.menu.BOD.2v7.bootloader.high_fuses=0b1101{bootloader.eesave_bit}101
 88.menu.BOD.4v3=BOD 4.3V
-88.menu.BOD.4v3.bootloader.high_fuses=0xd4
+88.menu.BOD.4v3.bootloader.high_fuses=0b1101{bootloader.eesave_bit}100
 88.menu.BOD.1v8=BOD 1.8V
-88.menu.BOD.1v8.bootloader.high_fuses=0xd6
+88.menu.BOD.1v8.bootloader.high_fuses=0b1101{bootloader.eesave_bit}110
 88.menu.BOD.disabled=BOD Disabled
-88.menu.BOD.disabled.bootloader.high_fuses=0xd7
+88.menu.BOD.disabled.bootloader.high_fuses=0b1101{bootloader.eesave_bit}111
 
 # Compiler link time optimization
 88.menu.LTO.Os=LTO Disabled
@@ -647,6 +666,12 @@ menu.bootloader=Bootloader
 48.menu.bootloader.no_bootloader.build.export_merged_output=false
 48.menu.bootloader.no_bootloader.bootloader.file=empty/empty.hex
 
+# EEPROM
+48.menu.eeprom.keep=EEPROM retained
+48.menu.eeprom.keep.bootloader.eesave_bit=0
+48.menu.eeprom.erase=EEPROM not retained
+48.menu.eeprom.erase.bootloader.eesave_bit=1
+
 # Variants
 48.menu.variant.modelP=48P / 48PA
 48.menu.variant.modelP.bootloader.cksel_bits=0111
@@ -665,13 +690,13 @@ menu.bootloader=Bootloader
 
 # Brown out detection
 48.menu.BOD.2v7=BOD 2.7V
-48.menu.BOD.2v7.bootloader.high_fuses=0xd5
+48.menu.BOD.2v7.bootloader.high_fuses=0b1101{bootloader.eesave_bit}101
 48.menu.BOD.4v3=BOD 4.3V
-48.menu.BOD.4v3.bootloader.high_fuses=0xd4
+48.menu.BOD.4v3.bootloader.high_fuses=0b1101{bootloader.eesave_bit}100
 48.menu.BOD.1v8=BOD 1.8V
-48.menu.BOD.1v8.bootloader.high_fuses=0xd6
-48.menu.BOD.disabled=BOD disabled
-48.menu.BOD.disabled.bootloader.high_fuses=0xd7
+48.menu.BOD.1v8.bootloader.high_fuses=0b1101{bootloader.eesave_bit}110
+48.menu.BOD.disabled=BOD Disabled
+48.menu.BOD.disabled.bootloader.high_fuses=0b1101{bootloader.eesave_bit}111
 
 # Compiler link time optimization
 48.menu.LTO.Os=LTO disabled
@@ -802,7 +827,7 @@ menu.bootloader=Bootloader
 8.bootloader.unlock_bits=0x3f
 8.bootloader.lock_bits=0x0f
 8.bootloader.low_fuses=0b{bootloader.bod_bits}{bootloader.sut_cksel_bits}
-8.bootloader.high_fuses=0b110{bootloader.ckopt_bit}010{bootloader.bootrst_bit}
+8.bootloader.high_fuses=0b110{bootloader.ckopt_bit}{bootloader.eesave_bit}10{bootloader.bootrst_bit}
 8.build.core=MCUdude_corefiles
 8.build.variant=standard
 8.build.board=AVR_ATmega8
@@ -824,6 +849,12 @@ menu.bootloader=Bootloader
 8.menu.bootloader.no_bootloader.bootloader.bootrst_bit=1
 8.menu.bootloader.no_bootloader.bootloader.file=empty/empty.hex
 
+# EEPROM
+8.menu.eeprom.keep=EEPROM retained
+8.menu.eeprom.keep.bootloader.eesave_bit=0
+8.menu.eeprom.erase=EEPROM not retained
+8.menu.eeprom.erase.bootloader.eesave_bit=1
+
 # Brown out detection - This is the first part of the low fuse bit concatenation
 8.menu.BOD.2v7=BOD 2.7V
 8.menu.BOD.2v7.bootloader.bod_bits=10