Worked on the nxp-upstream/zephyr repository to enhance the stability of the Renesas RA UART driver, focusing on resolving a transmission issue in non-FIFO configurations. Addressed a bug in the TX enable path by modifying the uart_ra_sci_irq_tx_enable() function to prevent clearing the transmit status when the FIFO is disabled, which previously led to sporadic re-sending of the last byte and potential data corruption. This targeted fix improved UART reliability and reduced edge-case failures during serial communication. The work involved C programming, embedded systems expertise, and driver development, demonstrating careful attention to low-level hardware behavior and system robustness.