The Intel IXP400 software provides generic support for the UARTs available on the IXP4XX network processors; however, the UARTS are fully supported by each operating system with native device drivers. The operating system drivers provide a standard serial port abstraction specific for each operating system. At this point, you probably do not need to use the Intel IXP400 UART software component.

The UARTs are modeled on the de facto industry standard 16550 UART. There are, however, some minor differences in the implementation and register map, which necessitate minor modification to the drivers that support the standard UART. Should you need to develop a device driver for the UART, you should start with a 16550 UART driver closest to your target and modify it to accommodate the differences. The differences to the standard implementation are as follows:

• UART FIFO depth. The IXP4XX network processors provide a FIFO of 64 bytes; the de facto standard is 16 bytes.

• Interrupt-enabled register. This register contains two additional bits: one to enable the UART (UUE bit), and the other to enable a receiver time out interrupt (RTOIE bit).

The UARTs support the clear to send (CTS) and request to send (RTS) flow control signals, but do not support any of the extended modem signals, such as data set ready, data terminal ready, data carrier detect, or ring indicator. If you require these additional signals, the GPIO pins are ideal.