How to make the bootloader start address at 0x7E00 ?

[rickygai]

I noticed the pre-built version of bootloader of atmega328pb is starting at address 0x7E00 for example under,

C:\MiniCore-3.1.3\avr\bootloaders\optiboot_flash\bootloaders\atmega328pb\22118400L
optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex

After written the above bootloader, arduino protocol able to recognize the bootloader.

BUT I want to create the bootloader manually, I tested AVR-GCC versions below all resulting in bootloader start at 0x7C00

5.4.0
7.3.0
15.2.0
16.1.0

May i know what version of AVR-GCC or right parameters to pass in from make command in order to create version identical to the pre-built version of bootloader .hex as mentioned above ?

Pre-built C:\MiniCore-3.1.3\avr\bootloaders\optiboot_flash\bootloaders\atmega328pb\22118400L
optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex

:107E000001C0B7C0112484B790E89093610010922C
:107E10006100882361F0982F9A70923041F081FFC1
:107E200002C097EF94BF282E80E0C6D0E9C085E05D
:107E30008093810082E08093C00088E18093C1003C
:107E400087E18093C40086E08093C2008EE0B4D0C6
:107E5000259A84E02AEB3AEF91E030938500209355
:107E6000840096BBB09BFECF1D9AA8954091C000A0
:107E700047FD02C0815089F793D0813479F490D0C6
:107E8000182FA0D0123811F480E004C088E0113817
:107E900009F083E07ED080E17CD0EECF823419F40B
:107EA00084E198D0F8CF853411F485E0FACF853598
:107EB00041F476D0C82F74D0D82FCC0FDD1F82D0DC
:107EC000EACF863519F484E085D0DECF843691F58B
:107ED00067D066D0F82E64D0D82E00E011E05801AB
:107EE0008FEFA81AB80A5CD0F80180838501FA10D8
:107EF000F6CF68D0F5E4DF1201C0FFCF50E040E0DC
:107F000063E0CE0136D08E01E0E0F1E06F0182E067
:107F1000C80ED11C4081518161E0C8012AD00E5F9A
:107F20001F4FF601FC10F2CF50E040E065E0CE01BB
:107F300020D0B1CF843771F433D032D0F82E30D086
:107F400041D08E01F80185918F0123D0FA94F11070
:107F5000F9CFA1CF853739F435D08EE11AD085E934
:107F600018D086E197CF813509F0A9CF88E024D0D9
:107F7000A6CFFC010A0167BFE895112407B600FCF3
:107F8000FDCF667029F0452B19F481E187BFE89594
:107F900008959091C00095FFFCCF8093C60008958E

**My custom built bootloader .hex:**
:107C000002C0C1C0FCC0112484B790E89093610009
:107C100010926100803061F0982F9A70923041F09C
:107C200081FF02C097EF94BF282E80E0CFD0E8C13B
:107C300082E08093C00088E18093C10085E1809359
:107C4000C40086E08093C2008EE0C0D0B3D08535FA
:107C500009F46AC088F4853409F464C040F48134BE
:107C600009F44EC0823409F45AC0B6D055C08135EB
:107C7000E1F788E0ABD0F9CF843709F46AC0B0F5FA
:107C8000863509F458C0843681F794D093D0F82E05
:107C900091D0E82E00E011E068010F5F1F4F8AD0FD
:107CA000F6018083F012F8CF97D06E018E2D00E0A0
:107CB00011E0853409F44AC040E050E063E0CE01B1
:107CC00062D000E011E0F8010E5F1F4F408151814A
:107CD00061E0C60158D082E0C80ED11CF012F3CF8B
:107CE00040E050E065E0CE014ED016C0853709F087
:107CF000BCCF72D08EE157D085E955D086E10BC05C
:107D000059D0182F69D0123811F480E004C088E0EF
:107D1000113809F083E047D080E145D097CF84E166
:107D200063D0FACF85E0FCCF45D0C82F43D0D82F01
:107D3000CC0FDD1F9ACF84E057D0E7CFF8016191D7
:107D40008F01C601AED08FEFC81AD80AF012F6CF55
:107D5000E3CF30D02FD0F82E2DD0D82E3DD08E01AD
:107D60008D2D853449F4FC0EC80193D01CD00F5FD3
:107D70001F4FF012F9CFD0CFF80185918F0113D0AA
:107D8000FA94D1F7C9CFFC010A0167BFE895112425
:107D900007B600FCFDCF667029F0452B19F481E190
:107DA00087BFE89508959091C00095FFFCCF809320
:107DB000C60008958091C00087FFFCCF8091C0006D
:107DC00084FD01C0A8958091C600089598E1909324
:107DD0006000809360000895EDDF803219F088E044
:107DE000F5DFFFCF84E1DFCFCF93C82FE3DFC150B2
:107DF000E9F7CF91F1CFCB01642FA901C4CF9F92B6
:107E0000AF92BF92CF92DF92EF92FF920F931F93A8
:107E1000CF93DF9358019E2C8B01E901C12CD12C0B
:107E2000CA14DB0429F4911441F188E0CFDFFFCFBD
:107E300040E050E063E0C801A6DFE12CF12CF7013F
:107E4000EC0FFD1F4591559161E0C701800F911F17
:107E50009ADF82E0E80EF11C80E8E816F10479F779
:107E600040E050E065E0C8018EDF8FEFC81AD80A05
:107E700000581F4FC058DF4FD3CFDF91CF911F91D4
:107E80000F91FF90EF90DF90CF90BF90AF909F90B9
:107E90000895F999FECF92BD81BDF89A992780B5D2
:107EA0000895262FF999FECF1FBA92BD81BD20BD3E
:0E7EB0000FB6F894FA9AF99A0FBE019608954B
:027FFE00000879
:0400000300007C007D
:00000001FF

Below is the make parameters used, but the custom built version of bootloader cannot be recognized by arduino protocol via USB.

# make atmega328pb OS=posix ENV=arduino \
BIGBOOT=1 AVR_FREQ=22118400UL BOOTSZ=1024 UART=0 BAUD_RATE=115200 LED=B5 \
CC=/c/avr-gcc-16.1.0-x64-windows/bin/avr-gcc \
OBJCOPY=/c/avr-gcc-16.1.0-x64-windows/bin/avr-objcopy \
OBJDUMP=/c/avr-gcc-16.1.0-x64-windows/bin/avr-objdump \
SIZE=/c/avr-gcc-16.1.0-x64-windows/bin/avr-size \
OPTIMIZE='-Os' \
CFLAGS='-fno-inline-small-functions -fno-split-wide-types -mshort-calls -fno-tree-scev-cprop -fno-tree-loop-distribute-patterns'

I have read the C:\MiniCore-3.1.3\avr\bootloaders\optiboot_flash\bootloaders\atmega328pb\atmega328pb_build_info.txt 

Please advise what version of AVR-GCC or any other make commands/parameters used in order to create an identical bootloader based on Minicore pre-built bootloader **Pre-built C:\MiniCore-3.1.3\avr\bootloaders\optiboot_flash\bootloaders\atmega328pb\22118400L\
optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex** ?

[jg-noncelogic]

Remove BIGBOOT=1. That option, not the AVR-GCC version, moves this ATmega328PB build from 0x7E00 to 0x7C00.

In MiniCore 3.1.3, BIGBOOT=1 enables EEPROM upload and flash-page copy. The ATmega328PB rule then links at 0x7C00; without any of those three feature switches, it links at 0x7E00 and produces the non-_BIGBOOT file:

• BIGBOOT enables the two extra features
• ATmega328PB selects 0x7C00 or 0x7E00

Use a disposable second copy of MiniCore 3.1.3 so the build cannot overwrite your known-good packaged HEX. In Git Bash, run:

cd /c/path/to/disposable/MiniCore-3.1.3/avr/bootloaders/optiboot_flash

unset BIGBOOT SUPPORT_EEPROM COPY_FLASH_PAGES

make atmega328pb OS=posix \
  AVR_FREQ=22118400L BAUD_RATE=115200 \
  LED=B5 LED_START_FLASHES=2 UART=0 \
  CC=/c/avr-gcc-7.3.0-x64-windows/bin/avr-gcc \
  OBJCOPY=/c/avr-gcc-7.3.0-x64-windows/bin/avr-objcopy \
  OBJDUMP=/c/avr-gcc-7.3.0-x64-windows/bin/avr-objdump \
  SIZE=/c/avr-gcc-7.3.0-x64-windows/bin/avr-size

The output should be:

bootloaders/atmega328pb/22118400L/
optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex

The important differences from your command are:

1. remove BIGBOOT=1;
2. add LED_START_FLASHES=2, matching MiniCore’s bulk-build invocation (makeall);
3. remove BOOTSZ=1024, because this Makefile does not use a BOOTSZ variable; and
4. remove the supplied CFLAGS. The Makefile defines override CFLAGS, so command-line CFLAGS=... does not replace its normal flags (definition).

A make -n dry run from the v3.1.3 tree confirms the resolved linker address, feature defines, and filename: the command above resolves to --section-start=.text=0x7e00; adding BIGBOOT=1 changes it to 0x7c00, enables both extra features, and selects the _BIGBOOT.hex name. A dry run alone does not verify generated bytes.

I also built the revised configuration in a disposable v3.1.3 checkout with Arduino’s 7.3.0-atmel3.6.1-arduino4 AVR toolchain. The generated HEX was byte-for-byte identical to the checked-in file; both had SHA-256 3f55fa922aba2ef6ca9049c9e773dea4d0f02d80fae643b38d084c463f5fce46. The build reported 484 bytes, matching the later AVR-GCC 7.3.0 entry for this exact 22118400L / UART0 / B5 / 115200 artifact (build record). Your Windows bundle may contain different binutils or avr-libc builds despite the same GCC version label, so compare the generated HEX rather than assuming identity.

The Makefile and HEX use byte addresses. For an ATmega328PB bootloader entered on reset at 0x7E00, the required boot section is 256 words / 512 bytes (BOOTSZ[1:0]=11, datasheet word address 0x3F00) and BOOTRST must be programmed (0). A 0x7C00 image instead uses the 512-word / 1 KiB section (BOOTSZ[1:0]=10). See the ATmega328PB datasheet, Boot Loader Support.

Because your packaged 0x7E00 image already starts correctly, replacing it with another 0x7E00 image should not require changing the boot-size fuses. This answer covers building and inspection, not fuse writing or flashing. Before any write, preserve every unrelated fuse bit, especially the clock source, SPI programming, and reset-pin settings; keep a known-good HEX and working ISP recovery path available. Do not copy a complete raw fuse byte from another board.

Disclosure: this answer was drafted by an AI agent and independently checked for technical correctness, first-reader clarity, usefulness, and flashing safety.

[MCUdude]

Why would you want to use Opiboot and not Urboot? Urboot is better in every way.

[rickygai]

I have not yet try the Urboot, as mostly the name "optiboot" is known publicly :)

I mean, there must be reason why the optiboot flash able to produce the pre-built bootloader .hex starting address at 0x7E00 correctly that can be recognized by arduino protocol. I have used the common version of avr-gcc, i am not sure why the binary .hex generated is larger as you can see.

[rickygai]

jg-noncelogic
hi, can you share a .zip link for me to download the "Arduino’s 7.3.0-atmel3.6.1-arduino4 AVR toolchain" ?

I have to use BIGBOOT=1 in order to compile successfully, but it is loaded 0x7C00 with hfuse 0xD8 set, but arduino protocol still failed to talk to the bootloader.

without BIGBOOT, it resulted below,

# make atmega328pb OS=posix ENV=arduino AVR_FREQ=22118400L UART=0 BAUD_RATE=115200 LED=B5 LED_START_FLASHES=2 CC=/ucrt64/bin/avr-gcc OBJCOPY=/ucrt64/bin/avr-objcopy OBJDUMP=/ucrt64/bin/avr-objdump SIZE=/ucrt64/bin/avr-size OPTIMIZE='-Os -fno-inline-small-functions -fno-split-wide-types'
mkdir -p bootloaders/atmega328pb/22118400L
Using avr-gcc 16.1.0
\nUART = UART0\tLED_PIN = B5\t LED_FLASHES = 2\t SUPPORT_EEPROM = 0\t COPY_FLASH_PAGES = 0
\x1B[1m\x1B[4m
BAUD RATE CHECK: Desired: 115200 Real: 115200 UBRRL = 23 Difference: 0.0 %\x1B[0m
/ucrt64/bin/avr-gcc -g -Wall -Os -fno-inline-small-functions -fno-split-wide-types -mmcu=atmega328pb -DF_CPU=22118400L -DOPTIBOOT_CUSTOMVER=1 -DBAUD_RATE=115200 -DLED_START_FLASHES=2    -DLED=B5     -DUART=0 -Wl,--section-start=.text=0x7e00 -Wl,--section-start=.version=0x7ffe -Wl,--relax -nostartfiles -o bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf optiboot_flash.o
C:/msys64/ucrt64/bin/../lib/gcc/avr/16.1.0/../../../../avr/bin/ld.exe: section .version LMA [00007ffe,00007fff] overlaps section .text LMA [00007e00,000080bd]
collect2.exe: error: ld returned 1 exit status
make: [Makefile:1205: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf] Error 1 (ignored)

/ucrt64/bin/avr-size bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf
C:\msys64\ucrt64\bin\avr-size.exe: 'bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf': No such file
make: [Makefile:1207: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf] Error 1 (ignored)
/ucrt64/bin/avr-objcopy -j .text -j .data -j .version --set-section-flags .version=alloc,load -O ihex bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex
C:\msys64\ucrt64\bin\avr-objcopy.exe: 'bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf': No such file
make: *** [Makefile:1242: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex] Error 1

I have tried Arduino’s 7.3.0-atmel3.6.1-arduino7, it is the same result as shown above as well,

# make atmega328pb OS=posix \
AVR_FREQ=22118400L BAUD_RATE=115200 LED=B5 LED_START_FLASHES=2 UART=0 \
CC=/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc \
OBJCOPY=/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy \
OBJDUMP=/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objdump \
SIZE=/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-size
mkdir -p bootloaders/atmega328pb/22118400L
Using avr-gcc 7.3.0
\nUART = UART0\tLED_PIN = B5\t LED_FLASHES = 2\t SUPPORT_EEPROM = 0\t COPY_FLASH_PAGES = 0
\x1B[1m\x1B[4m
BAUD RATE CHECK: Desired: 115200 Real: 115200 UBRRL = 23 Difference: 0.0 %\x1B[0m
/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-gcc -g -Wall -Os -fno-split-wide-types -mrelax -mmcu=atmega328pb -DF_CPU=22118400L -DOPTIBOOT_CUSTOMVER=1 -DBAUD_RATE=115200 -DLED_START_FLASHES=2    -DLED=B5     -DUART=0 -Wl,--section-start=.text=0x7e00 -Wl,--section-start=.version=0x7ffe -Wl,--relax -nostartfiles -o bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf optiboot_flash.o
c:/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/../lib/gcc/avr/7.3.0/../../../../avr/bin/ld.exe: section .version loaded at [00007ffe,00007fff] overlaps section .text loaded at [00007e00,000080bd]
collect2.exe: error: ld returned 1 exit status
make: [Makefile:1205: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf] Error 1 (ignored)

/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-size bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf
C:\avr-gcc\7.3.0-atmel3.6.1-arduino7\bin\avr-size.exe: 'bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf': No such file
make: [Makefile:1207: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf] Error 1 (ignored)
/c/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy -j .text -j .data -j .version --set-section-flags .version=alloc,load -O ihex bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex
C:\avr-gcc\7.3.0-atmel3.6.1-arduino7\bin\avr-objcopy.exe: 'bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf': No such file
make: *** [Makefile:1242: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex] Error 1

[rickygai]

strange, I tried to download v3.1.3 HERE, and able to compile successfully, arduino protocol able to talk to the bootloader successfully.

# make atmega328pb OS=posix ENV=arduino AVR_FREQ=22118400L UART=0 BAUD_RATE=115200 LED=B5 CC=/c/arduino-1.8.11/hardware/tools/avr/bin/avr-gcc OBJCOPY=/c/arduino-1.8.11/hardware/tools/avr/bin/avr-objcopy OBJDUMP=/c/arduino-1.8.11/hardware/tools/avr/bin/avr-objdump SIZE=/c/arduino-1.8.11/hardware/tools/avr/bin/avr-size
mkdir -p bootloaders/atmega328pb/22118400L
/c/arduino-1.8.11/hardware/tools/avr/bin/avr-gcc -g -Wall -Os -fno-split-wide-types -mrelax -mmcu=atmega328pb -DF_CPU=22118400L -DOPTIBOOT_CUSTOMVER=1 -DBAUD_RATE=115200 -DLED_START_FLASHES=0    -DLED=B5     -DUART=0   -c -o optiboot_flash.o optiboot_flash.c
Using avr-gcc 7.3.0
\nUART = UART0\tLED_PIN = B5\t LED_FLASHES = \t SUPPORT_EEPROM = 0\t COPY_FLASH_PAGES = 0
\x1B[1m\x1B[4m
BAUD RATE CHECK: Desired: 115200 Real: 115200 UBRRL = 23 Difference: 0.0 %\x1B[0m
/c/arduino-1.8.11/hardware/tools/avr/bin/avr-gcc -g -Wall -Os -fno-split-wide-types -mrelax -mmcu=atmega328pb -DF_CPU=22118400L -DOPTIBOOT_CUSTOMVER=1 -DBAUD_RATE=115200 -DLED_START_FLASHES=0    -DLED=B5     -DUART=0 -Wl,--section-start=.text=0x7e00 -Wl,--section-start=.version=0x7ffe -Wl,--relax -nostartfiles -o bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf optiboot_flash.o

/c/arduino-1.8.11/hardware/tools/avr/bin/avr-size bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf
   text    data     bss     dec     hex filename
    438       0       0     438     1b6 bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf
/c/arduino-1.8.11/hardware/tools/avr/bin/avr-objcopy -j .text -j .data -j .version --set-section-flags .version=alloc,load -O ihex bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex
\nOutput file name: bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.hex
rm bootloaders/atmega328pb/22118400L/optiboot_flash_atmega328pb_UART0_115200_22118400L_B5.elf

I don't know why the same version 3.1.3 downloaded from HERE works normally but other site downloads cannot.

Anyway, thanks again.