Issues

• OTAUpdate::download() returns Error::Modem (-26) on realistic firmware sizes while the download succeeds

  arduino/ArduinoCore-renesas#558 · Filter by author NoahChristian opened on Oct 11, 2026

• ArduinoLEDMatrix set() function discards brightness parameters

  arduino/ArduinoCore-renesas#556 · Filter by author davidgsd opened on Oct 8, 2026

• Clarify/Fix hardware clock settings in TwoWire

  arduino/ArduinoCore-renesas#554 · Filter by author matt1986hias opened on Aug 19, 2026
  1

• Upload fails when sketch uses WDT

  type: imperfection
  arduino/ArduinoCore-renesas#553 · Filter by author per1234 opened on Aug 12, 2026
  1

• SPI: SPI.end() before SPI.begin() causes the board to become unresponsive

  arduino/ArduinoCore-renesas#552 · Filter by author JudjinGM opened on Jul 30, 2026

• Potential new board any available PID under Arduino's VID

  arduino/ArduinoCore-renesas#548 · Filter by author mbedNoobNinja opened on Jul 16, 2026

• goBootloader() does not enter the bootloader from a native-USB (SerialUSB) sketch on UNO R4 WiFi - a watchdog reset with the identical magic write does

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#547 · Filter by author zrudomino opened on Jul 12, 2026

• RA6M4 Compatibility?

  arduino/ArduinoCore-renesas#546 · Filter by author csajisynco opened on Jul 7, 2026

• Wire does not configure the I2C mode SCI pins correctly

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#543 · Filter by author 2sc1740 opened on May 19, 2026

• Watchdog programming problem

  arduino/ArduinoCore-renesas#536 · Filter by author lawsonkeith opened on Mar 4, 2026
  1

• Arduino_CAN library: Calling available() twice in a row returns gives different results

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#535 · Filter by author lukasbraendli opened on Mar 3, 2026

• Arduino_CAN library: Calling if (CAN1.available()) causes message loss on the other interface

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#534 · Filter by author hamatyo0126 opened on Mar 1, 2026
  1

• R7FA6M5_CAN: CAN error interrupt handler incomplete — device stuck in infinite ISR loop on bus error

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#532 · Filter by author lukasbraendli opened on Feb 23, 2026

• R7FA4M1AB.h GTCR_b.TPCS definition is off by one bit

  topic: infrastructuretype: imperfection
  arduino/ArduinoCore-renesas#531 · Filter by author Skidlz opened on Feb 18, 2026

• Make HardwareSerial::write(buf, len) non-blocking

  topic: codetype: enhancement
  arduino/ArduinoCore-renesas#529 · Filter by author gicking opened on Feb 6, 2026

• SoftwareSerial destructor not complete

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#525 · Filter by author gicking opened on Feb 1, 2026

• Long delay for Serial1.begin() / missing updateBaudRate()

  arduino/ArduinoCore-renesas#524 · Filter by author gicking opened on Jan 25, 2026
  4

• SoftwareSerial baudrate cannot be changed dynamically

  topic: code
  arduino/ArduinoCore-renesas#523 · Filter by author gicking opened on Jan 25, 2026
  1

• Missing SoftwareSerial.stopListening() and SoftwareSerial.listen()

  arduino/ArduinoCore-renesas#522 · Filter by author gicking opened on Jan 24, 2026

• Status of I2S support

  arduino/ArduinoCore-renesas#521 · Filter by author pschatzmann opened on Jan 21, 2026
  1

• Display garbage on OLED SSD1306 screen when using core version 1.5.2 for Arduino R4 Nano

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#520 · Filter by author vbturri opened on Jan 17, 2026
  8

• Imperfection Report: Arduino Portenta C33: CAN1.write() corrupts CAN0 RX FIFO (message RAM overlap)

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#513 · Filter by author hamatyo0126 opened on Dec 28, 2025

• Arduino Uno R4 Wifi UDP Delay

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#512 · Filter by author danielbchapman opened on Dec 18, 2025
  1

• lwipClient::write() returns 0 on failure instead of number of bytes written

  topic: codetype: imperfection
  arduino/ArduinoCore-renesas#511 · Filter by author iofarm opened on Dec 16, 2025

• CRITICAL: Bus fault in FspTimer.cpp on Arduino UNO R4 WiFi when calling set_period_ms() on unopened timer

  arduino/ArduinoCore-renesas#509 · Filter by author gip2 opened on Dec 5, 2025