In the stratified world of computing, the graphic processing unit (GPU) and the central processor (CPU) receive the lion’s share of attention. Yet, the humble UART (Universal Asynchronous Receiver-Transmitter) remains the unsung workhorse of infrastructure. At the heart of many industrial, telecommunications, and legacy enterprise systems lies a specific breed of this technology: the 16c95x family. The software that brings it to life—the 16c95x Serial Port Driver —is a masterclass in managing latency, throughput, and hardware complexity.

The next time you issue screen /dev/ttyS0 115200 , pause to appreciate the thousands of lines of kernel code that are, at that very moment, carefully policing the flow of bits through a 64-byte FIFO, ensuring that not a single character of your prompt is lost to the entropy of asynchronous transmission.

static const struct serial_rs485 serial_rs485_supported = .flags = SER_RS485_ENABLED ; static const struct uart_ops exar_ops = .tx_empty = exar_tx_empty, .set_mctrl = exar_set_mctrl, .start_tx = exar_start_tx, .stop_tx = exar_stop_tx, .handle_irq = exar_handle_irq, // The heart of the driver .startup = exar_startup, .shutdown = exar_shutdown, .set_termios = exar_set_termios, // Where baud, parity, flow are set ;

To understand the driver is to understand a negotiation between a high-speed, interrupt-driven CPU and a comparatively slow, asynchronous, bit-shifting piece of silicon. Most developers cut their teeth on the 16550 UART—a 16-byte FIFO (First-In-First-Out) device that was revolutionary in the early 1990s. The 16c95x, however, is a different beast. It is a high-performance, multi-channel UART. Variants like the 16c954 or 16c955 offer two, four, or even eight independent serial ports on a single chip.