# Can only upload the program in bootloader mode

**URL:** <https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701>\
**Category:** UNO R4 WiFi\
**Created:** [December 31, 2025, 12:28pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701 "2025-12-31T12:28:05Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![suikachi](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suikachi/32/1253331_2.png) [@suikachi](https://forum.arduino.cc/u/suikachi)\
**Post date:** [December 31, 2025, 12:28pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/1 "2025-12-31T12:28:05Z")

</div>

the upload log on Arduino IDE 2.3.7:

```arduino
bossac -d --port=COM3 -U -e -w Blink.ino.bin -R
Set binary mode
Send auto-baud
Set binary mode
No device found on COM3
exit status 1

```

My board won't allow upload after an upload unless it's in bootloader mode, but the SSD1306 screen isn't working with this upload way, what's going on?

---

<div class="post-metadata">

**Author:** ![sonofcy](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/sonofcy/32/1283617_2.png) [@sonofcy](https://forum.arduino.cc/u/sonofcy)\
**Post date:** [December 31, 2025, 1:08pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/2 "2025-12-31T13:08:59Z")

</div>

What board?

post verbose error log in code tags so we can see what is going on.

 ![Screenshot 2025-12-31 at 08.08.17](https://europe1.discourse-cdn.com/arduino/original/4X/9/6/2/962bdaf559564e19862f7e112ca44910d146b13f.png)

---

<div class="post-metadata">

**Author:** ![suikachi](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suikachi/32/1253331_2.png) [@suikachi](https://forum.arduino.cc/u/suikachi)\
**Post date:** [December 31, 2025, 1:13pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/3 "2025-12-31T13:13:59Z")

</div>

Arduino Uno R4 Wifi

the logs on uploading, sorry for lots of Chinese appear if not understandable:

```arduino
FQBN: arduino:renesas_uno:unor4wifi
使用檔案夾: C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1 裏面平台的開發板 'unor4wifi'  
使用檔案夾: C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1 裏面平台的核心 'arduino' 

檢測有使用的程式庫...
C:\Users\chara\AppData\Local\Arduino15\packages\arduino\tools\arm-none-eabi-gcc\7-2017q4/bin/arm-none-eabi-g++ -c -w -Os -g3 -fno-use-cxa-atexit -fno-rtti -fno-exceptions -nostdlib -DF_CPU=48000000 -DNO_USB -DBACKTRACE_SUPPORT -DARDUINO_UNOR4_WIFI -std=gnu++17 -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsigned-char -ffunction-sections -fdata-sections -fmessage-length=0 -fno-builtin -w -x c++ -E -CC -DARDUINO=10607 -DPROJECT_NAME="C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino" -DARDUINO_UNOWIFIR4 -DARDUINO_ARCH_RENESAS_UNO -DARDUINO_ARCH_RENESAS -DARDUINO_FSP -D_XOPEN_SOURCE=700 -mthumb @C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4/defines.txt -DCFG_TUSB_MCU=OPT_MCU_RAXXX -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/tinyusb -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/api/deprecated -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/api/deprecated-avr-comp -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4 -iprefixC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1 @C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4/includes.txt C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\sketch\BareMinimum.ino.cpp -o nul
生成函式原型...
C:\Users\chara\AppData\Local\Arduino15\packages\arduino\tools\arm-none-eabi-gcc\7-2017q4/bin/arm-none-eabi-g++ -c -w -Os -g3 -fno-use-cxa-atexit -fno-rtti -fno-exceptions -nostdlib -DF_CPU=48000000 -DNO_USB -DBACKTRACE_SUPPORT -DARDUINO_UNOR4_WIFI -std=gnu++17 -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsigned-char -ffunction-sections -fdata-sections -fmessage-length=0 -fno-builtin -w -x c++ -E -CC -DARDUINO=10607 -DPROJECT_NAME="C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino" -DARDUINO_UNOWIFIR4 -DARDUINO_ARCH_RENESAS_UNO -DARDUINO_ARCH_RENESAS -DARDUINO_FSP -D_XOPEN_SOURCE=700 -mthumb @C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4/defines.txt -DCFG_TUSB_MCU=OPT_MCU_RAXXX -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/tinyusb -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/api/deprecated -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino/api/deprecated-avr-comp -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\cores\arduino -IC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4 -iprefixC:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1 @C:\Users\chara\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.5.1\variants\UNOWIFIR4/includes.txt C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\sketch\BareMinimum.ino.cpp -o C:\Users\chara\AppData\Local\Temp\3238642615\sketch_merged.cpp
C:\Users\chara\AppData\Local\Arduino15\packages\builtin\tools\ctags\5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives C:\Users\chara\AppData\Local\Temp\3238642615\sketch_merged.cpp

編譯 sketch ...
"C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-g++" -c -w -Os -g3 -fno-use-cxa-atexit -fno-rtti -fno-exceptions -MMD -nostdlib -DF_CPU=48000000 -DNO_USB -DBACKTRACE_SUPPORT -DARDUINO_UNOR4_WIFI -MMD -std=gnu++17 -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsigned-char -ffunction-sections -fdata-sections -fmessage-length=0 -fno-builtin -DARDUINO=10607 "-DPROJECT_NAME=\"C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino\"" -DARDUINO_UNOWIFIR4 -DARDUINO_ARCH_RENESAS_UNO -DARDUINO_ARCH_RENESAS -DARDUINO_FSP -D_XOPEN_SOURCE=700 -mthumb "@C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4/defines.txt" -DCFG_TUSB_MCU=OPT_MCU_RAXXX "-IC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\cores\\arduino/tinyusb" "-IC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\cores\\arduino/api/deprecated" "-IC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\cores\\arduino/api/deprecated-avr-comp" "-IC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\cores\\arduino" "-IC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4" "-iprefixC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1" "@C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4/includes.txt" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\sketch\\BareMinimum.ino.cpp" -o "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\sketch\\BareMinimum.ino.cpp.o"
編譯程式庫...
編譯核心...
使用先前編譯的檔案: C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\core\tmp_gen_c_files\common_data.c.o
使用先前編譯的檔案: C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\core\tmp_gen_c_files\main.c.o
使用先前編譯的檔案: C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\core\tmp_gen_c_files\pin_data.c.o
使用先前編譯的檔案: C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310\core\variant.cpp.o
使用預編譯核心: C:\Users\chara\AppData\Local\arduino\cores\arduino_renesas_uno_unor4wifi_e9d839c0e73cd97c6a00a5733704f7f4\core.a
將所有內容鏈接在一起...
"C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-g++" -Wl,--gc-sections --specs=nosys.specs -w -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -o "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.elf" "-LC:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310" "-LC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4" "-TC:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4/fsp.ld" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\sketch\\BareMinimum.ino.cpp.o" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\core\\tmp_gen_c_files\\common_data.c.o" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\core\\tmp_gen_c_files\\main.c.o" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\core\\tmp_gen_c_files\\pin_data.c.o" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310\\core\\variant.cpp.o" -Wl,--whole-archive -Wl,--start-group "C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.5.1\\variants\\UNOWIFIR4/libs/libfsp.a" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/..\\..\\cores\\arduino_renesas_uno_unor4wifi_e9d839c0e73cd97c6a00a5733704f7f4\\core.a" -Wl,--no-whole-archive --specs=nano.specs -lstdc++ -lsupc++ -lm -lc -lgcc -lnosys -Wl,--end-group "-Wl,-Map,C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.map"
"C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-objcopy" -O binary -j .text -j .data "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.elf" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.bin"
"C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-objcopy" -O ihex -j .text -j .data "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.elf" "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.hex"
"C:\\Users\\chara\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-size" -A "C:\\Users\\chara\\AppData\\Local\\arduino\\sketches\\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.elf"
Sketch 使用 51824 位元組（19%）的程式儲存空間。最大為 262144 位元組
全域變數使用 6740 位元組 (20%) 的動態記憶體, 保留 26028 位元組給區域變數. 最大 32768 位元組
在 COM2 連接埠上執行 1200-bps TOUCH 重置
"C:\Users\chara\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.9.1-arduino5/bossac" -d --port=COM2 -U -e -w "C:\Users\chara\AppData\Local\arduino\sketches\E67D7A0E6BC091E98D39CB958270C310/BareMinimum.ino.bin" -R
Set binary mode
Send auto-baud
Set binary mode
No device found on COM2
上傳失敗: 上傳錯誤: exit status 1

```

---

<div class="post-metadata">

**Author:** ![KurtE](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kurte/32/1246572_2.png) [@KurtE](https://forum.arduino.cc/u/KurtE)\
**Post date:** [December 31, 2025, 2:31pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/4 "2025-12-31T14:31:23Z")

</div>

Make sure you have the right Com port selected for the UNO R4

Your first post showed: COM3 and last one showed COM2.  
Also make sure no other app has the com port open.

It has been awhile since I did anything with R4, but if I remember correctly, I also ran into  
issue similar if the sketch you are currently running has hung or crashed. But if it is  
running something like blink it should work.

---

<div class="post-metadata">

**Author:** ![sonofcy](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/sonofcy/32/1283617_2.png) [@sonofcy](https://forum.arduino.cc/u/sonofcy)\
**Post date:** [December 31, 2025, 2:51pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/5 "2025-12-31T14:51:08Z")

</div>

That log looks short, also I don;t remember seeing those messages at the bottom but I haven't looked in a while.  
It looks like you have not selected the correct port.

---

<div class="post-metadata">

**Author:** ![suikachi](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suikachi/32/1253331_2.png) [@suikachi](https://forum.arduino.cc/u/suikachi)\
**Post date:** [December 31, 2025, 3:17pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/6 "2025-12-31T15:17:32Z")

</div>

sorry but I heard something weird advice from AI and edit the COM3 to COM2, I already change it back, and I'm sure that COM3 not using by any programs.

The program actually work and blinking if I upload it with bootloader mode, but the problem is I can't upload the programs into board normally.

---

<div class="post-metadata">

**Author:** ![KurtE](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kurte/32/1246572_2.png) [@KurtE](https://forum.arduino.cc/u/KurtE)\
**Post date:** [December 31, 2025, 3:37pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/7 "2025-12-31T15:37:25Z")

</div>

After you start up the R4, what shows up in the tools-\>Port menu?  
Does it show an entry for the R4 and is it selected?

When you are in bootloader mode it does not matter that the com port is off as it  
looks for it as a specific USB type...

If you have the Serial monitor pane open, try closing it.

Try running a simple sketch like:

```arduino
void setup() {
  Serial.begin(115200);
}

int loop_count = 0;
void loop() {
    Serial.println(loop_count++);
    delay(1000);
}

```

If you load it and have the Serial monitor open does it output to it?  
Can you then load a different program?

---

<div class="post-metadata">

**Author:** ![suikachi](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suikachi/32/1253331_2.png) [@suikachi](https://forum.arduino.cc/u/suikachi)\
**Post date:** [December 31, 2025, 3:42pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/8 "2025-12-31T15:42:50Z")

</div>

COM3 (Arduino UNO R4 Wifi), yes.  
It will output numbers.  
No, still can't upload normally, but the error log changed:

```arduino
Set binary mode
Send auto-baud
Set binary mode
version()=73
Connected at 115200 baud
readWord(addr=0)=0xa0d3437
readWord(addr=0xe000ed00)=0xa0d3537
readWord(addr=0x400e0740)=0xa0d3637
readWord(addr=0x400e0744)=0xa0d3737

Device unsupported
上傳失敗: 上傳錯誤: exit status 1

```

---

<div class="post-metadata">

**Author:** ![suikachi](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suikachi/32/1253331_2.png) [@suikachi](https://forum.arduino.cc/u/suikachi)\
**Post date:** [January 1, 2026, 12:40pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/9 "2026-01-01T12:40:18Z")

</div>

I found the problem that my wire was connected to the RST pin instead of the VCC pin, sorry for wasting you all's time:(

---

<div class="post-metadata">

**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [June 30, 2026, 12:41pm UTC](https://forum.arduino.cc/t/can-only-upload-the-program-in-bootloader-mode/1422701/10 "2026-06-30T12:41:04Z")

</div>

Closed on June 30, 2026, 12:41pm UTC

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