Non-POSIX line speeds

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The interface to serial devices specified by POSIX and subsequent UNIX standards such as X/OPEN relies on the termios data structure, defined in /usr/include/termios.h. Unfortunately, that data structure cannot be used to specify line speeds in excess of 38,400 bits per second. Most serial hardware currently in use can support speeds of up to 230,000 bps. To use these higher line speeds on AIX, the desired speed should be specified when configuring the port using SMIT. If the serial port hardware (UART) can support your specified line speed, the port can be configured.

Get attribute ioctls using the termio or termios structure will report the line speed as 50 bps. The non-POSIX line speed will be used by the port until changed, so applications using set attribute ioctls with the termio and termios structure should not modify the CBAUD flags unless they really do intend to change the line speed. If the serial port hardware (UART) cannot support the requested line speed, the port fails to configure and an error is returned.

Note: The 8- and 128-port PCI adapters support non-POSIX line speeds of 115,200 and 230,000 bps only. The 128-port PCI adapter has an additional constraint of 2.5 Mbps aggregate bandwidth (with the 8-wire cable), which would be completely consumed by 11 devices transferring at a sustained 230,000 bps each. This constraint is on the line connecting the adapter to the RANs, so a single adapter can be completely consumed by 22 such devices.