So for certain internal modems you will need to specify this parameter so Linux can initialize the UARTcorrectly. Some internal modems do not have National Semiconductor compatible UART's, but have cheap imitations instead.Some of these cheasy imitations UART's do not fully support the loopback detection mode, which is used by the kernel to make sure there really is a UART at aparticular address before attempting to configure it. skip_test During autoconfiguration, skip the UART test. ^auto_irq During autoconfiguration, do not try to determine the IRQ. It is generally safer not to use the auto_irq feature, but rather to specify the IRQ to be used explicitly, using the irqparameter. This feature is not guaranteed to always produce the correct result some hardware configurations willfool the Linux kernel. auto_irq During autoconfiguration, try to determine the IRQ.

The I/O port must be correctlyset the kernel will attempt to determine the UART type, and if the auto_irq parameter is set, Linux will attempt to automatically determine the IRQ.The autoconfig parameter should be given after the port, auto_irq, and skip_test parameters have been specified. autoconfig When this parameter is given, setserial will ask the kernel to attempt to automatically configure the serial port. These UART's usually have other problems: the skip_testparameter also often must be specified. If you attempt to override thisusing the uart parameter, you will see dropped characters during file transmissions. This is important, because they do not have a transmit FIFO.Hence, they are not compatible with a 16550A UART, and the autoconfiguration process will correctly identify them as 16450's. They do not have really have a 16550A compatible UART insteadwhat they have is a 16450 compatible UART with a 1k receive buffer to prevent receiver overruns. Some internal modems are billed as having a '16550A UART with a 1k buffer'.

Openwrt usb serial ftdi