The Tx interrupt (THRE – Transmitter Holding Register Empty) asserts when the Tx FIFO falls below the programmed trigger level (default empty). The driver’s Tx ISR should fill the FIFO up to its capacity or until the Tx buffer is empty.
What are you using (e.g., Windows 10 64-bit, Windows 11, Linux)? 16c95x serial port driver
In bare-metal systems, the driver often runs in a polled mode or simple interrupt context. With an RTOS like FreeRTOS, you can implement a proper serial driver with task notifications: The Tx interrupt (THRE – Transmitter Holding Register