freebsd-dev/share/man/man4/uart.4

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The uart(4) driver is an universal driver for various UART hardware. It improves on sio(4) in the following areas: o Fully newbusified to allow for memory mapped I/O. This is a must for ia64 and sparc64, o Machine dependent code to take full advantage of machine and firm- ware specific ways to define serial consoles and/or debug ports. o Hardware abstraction layer to allow the driver to be used with various UARTs, such as the well-known ns8250 family of UARTs, the Siemens sab82532 or the Zilog Z8530. This is especially important for pc98 and sparc64 where it's common to have different UARTs, o The notion of system devices to unkludge low-level consoles and remote gdb ports and provides the mechanics necessary to support the keyboard on sparc64 (which is UART based). o The notion of a kernel interface so that a UART can be tied to something other than the well-known TTY interface. This is needed on sparc64 to present the user with a device and ioctl handling suitable for a keyboard, but also allows us to cleanly hide an UART when used as a debug port. Following is a list of features and bugs/flaws specific to the ns8250 family of UARTs as compared to their support in sio(4): o The uart(4) driver determines the FIFO size and automaticly takes advantages of larger FIFOs and/or additional features. Note that since I don't have sufficient access to 16[679]5x UARTs, hardware flow control has not been enabled. This is almost trivial to do, provided one can test. The downside of this is that broken UARTs are more likely to not work correctly with uart(4). The need for tunables or knobs may be large enough to warrant their creation. o The uart(4) driver does not share the same bumpy history as sio(4) and will therefore not provide the necessary hooks, tweaks, quirks or work-arounds to deal with once common hardware. To that extend, uart(4) supports a subset of the UARTs that sio(4) supports. The question before us is whether the subset is sufficient for current hardware. o There is no support for multiport UARTs in uart(4). The decision behind this is that uart(4) deals with one EIA RS232-C interface. Packaging of multiple interfaces in a single chip or on a single expansion board is beyond the scope of uart(4) and is now mostly left for puc(4) to deal with. Lack of hardware made it impossible to actually implement such a dependency other than is present for the dual channel SAB82532 and Z8350 SCCs. The current list of missing features is: o No configuration capabilities. A set of tunables and sysctls is being worked out. There are likely not going to be any or much compile-time knobs. Such configuration does not fit well with current hardware. o No support for the PPS API. This is partly dependent on the ability to configure uart(4) and partly dependent on having sufficient information to implement it properly. As usual, the manpage is present but lacks the attention the software has gotten.
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.\"
.\" Copyright (c) 2003 Marcel Moolenaar
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.\" $FreeBSD$
.\"
.Dd August 25, 2003
.Dt UART 4
.Os
.\"
.Sh NAME
.Nm uart
.Nd driver for Universal Asynchronous Receiver/Transmitter (UART) devices
.\"
.Sh SYNOPSIS
.Cd "device uart"
.Pp
.Cd "device puc"
.Cd "device uart"
.\"
.Sh DESCRIPTION
The
.Nm
device driver provides support for various classes of UARTs implementing the
EIA RS-232C (CCITT V.24) serial communications interface.
2004-06-21 17:42:49 +00:00
Each such interface is controlled by a separate and independent instance of
The uart(4) driver is an universal driver for various UART hardware. It improves on sio(4) in the following areas: o Fully newbusified to allow for memory mapped I/O. This is a must for ia64 and sparc64, o Machine dependent code to take full advantage of machine and firm- ware specific ways to define serial consoles and/or debug ports. o Hardware abstraction layer to allow the driver to be used with various UARTs, such as the well-known ns8250 family of UARTs, the Siemens sab82532 or the Zilog Z8530. This is especially important for pc98 and sparc64 where it's common to have different UARTs, o The notion of system devices to unkludge low-level consoles and remote gdb ports and provides the mechanics necessary to support the keyboard on sparc64 (which is UART based). o The notion of a kernel interface so that a UART can be tied to something other than the well-known TTY interface. This is needed on sparc64 to present the user with a device and ioctl handling suitable for a keyboard, but also allows us to cleanly hide an UART when used as a debug port. Following is a list of features and bugs/flaws specific to the ns8250 family of UARTs as compared to their support in sio(4): o The uart(4) driver determines the FIFO size and automaticly takes advantages of larger FIFOs and/or additional features. Note that since I don't have sufficient access to 16[679]5x UARTs, hardware flow control has not been enabled. This is almost trivial to do, provided one can test. The downside of this is that broken UARTs are more likely to not work correctly with uart(4). The need for tunables or knobs may be large enough to warrant their creation. o The uart(4) driver does not share the same bumpy history as sio(4) and will therefore not provide the necessary hooks, tweaks, quirks or work-arounds to deal with once common hardware. To that extend, uart(4) supports a subset of the UARTs that sio(4) supports. The question before us is whether the subset is sufficient for current hardware. o There is no support for multiport UARTs in uart(4). The decision behind this is that uart(4) deals with one EIA RS232-C interface. Packaging of multiple interfaces in a single chip or on a single expansion board is beyond the scope of uart(4) and is now mostly left for puc(4) to deal with. Lack of hardware made it impossible to actually implement such a dependency other than is present for the dual channel SAB82532 and Z8350 SCCs. The current list of missing features is: o No configuration capabilities. A set of tunables and sysctls is being worked out. There are likely not going to be any or much compile-time knobs. Such configuration does not fit well with current hardware. o No support for the PPS API. This is partly dependent on the ability to configure uart(4) and partly dependent on having sufficient information to implement it properly. As usual, the manpage is present but lacks the attention the software has gotten.
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the
.Nm
driver.
The primary support for devices that contain multiple serial interfaces or
that contain other functionality besides one or more serial interfaces is
provided by the
.Xr puc 4
device driver.
However, the serial interfaces of those devices that are managed by the
.Xr puc 4
driver are controlled by the
.Nm
driver.
As such, the
.Xr puc 4
driver provides umbrella functionality for the
.Nm
driver and hides the complexities that are inherent when elementary components
are packaged together.
.Pp
The
.Nm
driver has a modular design to allow it to be used on differing hardware and
for various purposes.
In the following sections the components are discussed in detail.
Options are described in the section that covers the component to which each
option applies.
.\"
.Ss CORE COMPONENT
At the heart of the
.Nm
driver is the core component.
It contains the bus attachments and the low-level interrupt handler.
The uart(4) driver is an universal driver for various UART hardware. It improves on sio(4) in the following areas: o Fully newbusified to allow for memory mapped I/O. This is a must for ia64 and sparc64, o Machine dependent code to take full advantage of machine and firm- ware specific ways to define serial consoles and/or debug ports. o Hardware abstraction layer to allow the driver to be used with various UARTs, such as the well-known ns8250 family of UARTs, the Siemens sab82532 or the Zilog Z8530. This is especially important for pc98 and sparc64 where it's common to have different UARTs, o The notion of system devices to unkludge low-level consoles and remote gdb ports and provides the mechanics necessary to support the keyboard on sparc64 (which is UART based). o The notion of a kernel interface so that a UART can be tied to something other than the well-known TTY interface. This is needed on sparc64 to present the user with a device and ioctl handling suitable for a keyboard, but also allows us to cleanly hide an UART when used as a debug port. Following is a list of features and bugs/flaws specific to the ns8250 family of UARTs as compared to their support in sio(4): o The uart(4) driver determines the FIFO size and automaticly takes advantages of larger FIFOs and/or additional features. Note that since I don't have sufficient access to 16[679]5x UARTs, hardware flow control has not been enabled. This is almost trivial to do, provided one can test. The downside of this is that broken UARTs are more likely to not work correctly with uart(4). The need for tunables or knobs may be large enough to warrant their creation. o The uart(4) driver does not share the same bumpy history as sio(4) and will therefore not provide the necessary hooks, tweaks, quirks or work-arounds to deal with once common hardware. To that extend, uart(4) supports a subset of the UARTs that sio(4) supports. The question before us is whether the subset is sufficient for current hardware. o There is no support for multiport UARTs in uart(4). The decision behind this is that uart(4) deals with one EIA RS232-C interface. Packaging of multiple interfaces in a single chip or on a single expansion board is beyond the scope of uart(4) and is now mostly left for puc(4) to deal with. Lack of hardware made it impossible to actually implement such a dependency other than is present for the dual channel SAB82532 and Z8350 SCCs. The current list of missing features is: o No configuration capabilities. A set of tunables and sysctls is being worked out. There are likely not going to be any or much compile-time knobs. Such configuration does not fit well with current hardware. o No support for the PPS API. This is partly dependent on the ability to configure uart(4) and partly dependent on having sufficient information to implement it properly. As usual, the manpage is present but lacks the attention the software has gotten.
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.\"
.Ss HARDWARE DRIVERS
The core component and the kernel interfaces talk to the hardware through the
hardware interface.
This interface serves as an abstraction of the hardware and allows varying
UARTs to be used for serial communications.
.\"
.Ss SYSTEM DEVICES
System devices are UARTs that have a special purpose by way of hardware
design or software setup.
For example, Sun UltraSparc machines use UARTs as their keyboard interface.
Such an UART cannot be used for general purpose communications.
Likewise, when the kernel is configured for a serial console, the
corresponding UART will in turn be a system device so that the kernel can
output boot messages early on in the boot process.
.\"
.Ss KERNEL INTERFACES
The last but not least of the components is the kernel interface.
This component ultimately determines how the UART is made visible to the
kernel in particular and to users in general.
The default kernel interface is the TTY interface.
This allows the UART to be used for terminals, modems and serial line IP
applications.
System devices, with the notable exception of serial consoles, generally
have specialized kernel interfaces.
.\"
.Sh SEE ALSO
.Xr puc 4
.\"
.Sh HISTORY
The
.Nm
device driver first appeared in
.Fx 5.2 .
.Sh AUTHORS
This manual page was written by
.An Marcel Moolenaar Aq marcel@xcllnt.net .