ChorusOS man pages section 9DRV: Driver Implementations

ns16650(9DRV)

NAME

ns16550- generic ns16x50 compatible uart device driver

Synopsis

drv/src/uart/ns16550/ns16550.h         - ns16x50 hardware related constants
drv/src/uart/ns16550/ns16550.c          - driver code
drv/src/uart/ns16550/ns16550Prop.h   - driver specific properties

FEATURES

DRV

DESCRIPTION

Implements the ns16550 device driver interface.

EXTENDED DESCRIPTION

The ns16550 uart driver implements the uart device driver interface. The driver works on a uart device which is software compatible with the ns16x50 chip.

The driver uses the common bus driver interface provided by a parent bus driver. Thus, the driver is generic and may be applied to any bus providing this type of interface.

The ns16x50 driver does not provide the drv_probe() routine. In other words, the ns16x50 driver does not enumerate the bus, nor does it detect an ns16x50 device or create an associated device node. When the ns16x50 driver is used, associated device nodes should be created either statically by a boot program or dynamically by a separate bus enumerator driver. Such an enumerator driver could be developed for this particular bus architecture.

The driver does not provide the drv_bind() routine. In other words, the driver does not support dynamic driver-to-device binding. When the ns16x50 driver is used, the driver should be explicitly bound to the device using the PROP_DRIVER property. It is assumed that the device-to-driver binding is done either by a device node creator or by a separate binder driver. Such a driver-to-device binder could be developed for this particular bus architecture.

The driver provides the drv_unload() entry and supports driver component unloading. This allows the driver component to be unloaded if it is no longer being used and if it has been dynamically loaded at run time.

The driver supports all bus events specified by the common bus driver interface. As a consequence, the driver may be used with a hot-pluggable bus (for example, PCMCIA). The Table below summarizes the characteristics of the ns16x50 uart driver:

driver name:	"chorus@bus-ns16550-uart"
hardware:	NS16x50 compatible UART chip
exported interface:	"uart" (UART_CLASS)
exported interface version:	0 (UART_VERSION_INITIAL)
imported parent interface:	"bus" (BUS_CLASS)
minimal parent interface version:	0 (BUS_VERSION_INITIAL)
device probing (auto-detection):	not supported
driver unloading:	supported
system (emergency) shut-down:	supported
normal device shut-down:	supported
hot-plug (surprise) device removal:	supported

The table below lists device node properties used by the ns16550 driver.

Note that the column "m/o" specifies whether a given property is mandatory or optional. For optional properties, the column "default value" shows a default value which is used by the driver when a given property is not specified.

Name	Alias	Type	m/o	Default Value
"io-regs"	BUS_PROP_IO_REGS	<bus class specific>	m
"intr"	BUS_PROP_INTR	<bus class specific>	m
"clock-freq"	PROP_CLOCK_FREQ	PropClockFreq	o	1843200

The BUS_PROP_IO_REGS property specifies the ns16x50 I/O registers range. The property value is bus class specific.

The BUS_PROP_INTR property specifies the ns16x50 interrupt source. The property value is bus class specific.

ThePROP_CLOCK_FREQ property specifies the input clock frequency in Hz. By default, the input clock frequency is 1843200 Hz. Note that when programming the timer devisor for a given baud rate, the driver assumes the 16x clock factor. The formula relating the baud rate to the timer devisor is shown below.

<devisor> = (<clock-freq> + (8 * <baud-rate>)) / (16 * <baud-rate>)

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving