##Problem The serial RX line (PA9/DRXD) is set by Linux without the pull-up internal resistor. This could cause a lot of receiving interrupts from the debug serial port in noisy environments. ##Solution Change these lines in arch/arm/boot/dts/at91sam9x5dtsi: Original /* shared pinctrl settings */ dbgu { pinctrl_dbgu: dbgu-0 { atmel,pins = ; /* PA10 periph A with pullup */ }; }; Changed /* shared pinctrl settings */ dbgu { pinctrl_dbgu: dbgu-0 { atmel,pins = ; /* PA10 periph A with pullup */ }; }; then compile the dts following this article: * [Build linux kernel](/compile_linux_4_4)