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34 .Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices
48 device driver provides support for various classes of UARTs implementing the
49 EIA RS-232C (CCITT V.24) serial communications interface.
50 Each such interface is controlled by a separate and independent instance of
54 The primary support for devices that contain multiple serial interfaces or
55 that contain other functionality besides one or more serial interfaces is
61 However, the serial interfaces of those devices that are managed by the
65 driver are each independently controlled by the
72 driver provides umbrella functionality for the
74 driver and hides the complexities that are inherent when elementary components
75 are packaged together.
79 driver has a modular design to allow it to be used on differing hardware and
81 In the following sections the components are discussed in detail.
82 Options are described in the section that covers the component to which each
88 driver is the core component.
89 It contains the bus attachments and the low-level interrupt handler.
92 The core component and the kernel interfaces talk to the hardware through the
94 This interface serves as an abstraction of the hardware and allows varying
95 UARTs to be used for serial communications.
98 System devices are UARTs that have a special purpose by way of hardware
99 design or software setup.
100 For example, Sun UltraSparc machines use UARTs as their keyboard interface.
101 Such an UART cannot be used for general purpose communications.
102 Likewise, when the kernel is configured for a serial console, the
103 corresponding UART will in turn be a system device so that the kernel can
104 output boot messages early on in the boot process.
106 .Ss KERNEL INTERFACES
107 The last but not least of the components is the kernel interface.
108 This component ultimately determines how the UART is made visible to the
109 kernel in particular and to users in general.
110 The default kernel interface is the TTY interface.
111 This allows the UART to be used for terminals, modems and serial line IP
113 System devices, with the notable exception of serial consoles, generally
114 have specialized kernel interfaces.
119 driver supports the following classes of UARTs:
123 NS8250: standard hardware based on the 8250, 16450, 16550, 16650, 16750 or
126 SCC: serial communications controllers supported by the
132 .Bl -tag -width ".Pa /dev/ttyu?.init" -compact
135 .It Pa /dev/ttyu?.init
136 .It Pa /dev/ttyu?.lock
137 corresponding callin initial-state and lock-state devices
141 .It Pa /dev/cuau?.init
142 .It Pa /dev/cuau?.lock
143 corresponding callout initial-state and lock-state devices
152 device driver first appeared in
157 device driver and this manual page were written by
158 .An Marcel Moolenaar Aq marcel@xcllnt.net .