PROM Device Tree

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PROM Device Tree (Full Device Pathnames)

OpenBoot deals directly with the hardware devices in the system. Each device has a unique name that represents both the type of device and the location of that device in the device tree. The OpenBoot firmware builds a device tree for all devices from information gathered at the POST. Sun uses the device tree to organize devices that are attached to the system. The device tree is loaded into memory, to be used by the kernel during boot to identify all configured devices. The paths built in the device tree by OpenBoot vary, depending on the type of system and its device configuration. The following example shows a full device pathname for an older Sun system with SBus architecture, such as a SPARCstation 20:

/sbus@1f,0/esp@0,40000/sd@3,0:a

NOTE

The Device Tree Versus Device Pathname The terms device tree and device pathname are often interchanged, and you'll see both used. They both mean the same thing.

The following example shows the device tree for an internal disk on a peripheral component interconnect (PCI) bus system such as an Ultra 5:

/pci@1f,0/pci@1,1/ide@3/disk

Typically, the OBP uses disk and cdrom for the boot disk and CD-ROM drive.

The following example shows the disk device on an Ultra system with a PCI-SCSI bus:

/pci@1f,0/pci@1/isptwo@4/sd@3,0

A device tree is a series of node names separated by slashes (/).The top of the device tree is the root device node. Following the root device node, and separated by a leading slash /, is a bus nexus node. Connected to a bus nexus node is a leaf node, which is typically a controller for the attached device. Each device pathname has this form:

driver-name@unit-address:device-arguments

The components of the device pathname are described in Table 3.3.

Table 3.3 - Device Pathname Parameters

Parameter	Description
`driver-name`	This is the root device node, which is a human-readable string that consists of 1 to 31 letters, digits, and the following punctuation characters: , (comma) . (period) _ (underscore) + (plus sign) (minus sign) Uppercase and lowercase characters are distinct from one another. In some cases, the driver name includes the name of the device's manufacturer and the device's model name, separated by a comma. Typically, the manufacturer's uppercase, publicly listed stock symbol is used as the manufacturer's name (for example, `SUNW,hme0`). For built-in devices, the manufacturer's name is usually omitted (for example, `sbus` or `pci`). `@` must precede the address parameter; it serves as a separator between the driver name and unit address.
`unit-address`	A text string that represents the physical address of the device in its parent's address space. The exact meaning of a particular address depends on the bus to which the device is attached. In this example, `/sbus@3,0/SUNW,fas@3,0/sd@0,0` `sbus@3,0` represents the I/O board in slot 1, located on the back of the system, and `SUNW,fas@3,0` is the onboard fast/wide SCSI controller of the same board. The following are common device driver names: `fas`—Fast/wide SCSI controller. `hme`—Fast (10/100Mbps) Ethernet. `isp`—Differential SCSI controllers and the SunSwift card. `glm`—UltraSCSI controllers. `scsi`—SCSI devices. `sf`—SCSI-compliant nexus driver that supports the Fibre Channel Protocol for SCSI on Private Fibre Channel Arbitrated Loops (FC-ALs). `soc`—Serial optical controller (SOC) device driver. `socal`—The Fibre Channel host bus adapter, which is an SBus card that implements two full-duplex Fibre Channel interfaces. Each Fibre Channel interface can connect to an FC-AL. `sd@0,0` is the SCSI disk (`sd`) set to target `id 0`. (In this case, it is an internal disk because only internal disks should be controlled by the onboard SCSI controller of the I/O board in slot 1.)
`device-arguments`	A text string whose format depends on the particular device. `device-arguments` can be used to pass additional information to the device's software. In this example: `/pci@1f,0/pci@1,1/ide@3/atapicd@2,0:f` the argument for the disk device is `f`. The software driver for this device interprets its argument as a disk partition, so the device pathname refers to partition `f` on a CD-ROM.

You use the OpenBoot command show-devs to obtain information about the device tree and to display device pathnames. This command displays all the devices known to the system directly beneath a given device in the device hierarchy. show-devs used by itself shows the entire device tree. The syntax is as follows:

ok show-devs

The system outputs the entire device tree, as follows:

/SUNW,UltraSPARC-IIi@0,0
/pci@1f,0
/virtual-memory
/memory@0,10000000
/aliases
/options
/openprom
/chosen
/packages
/pci@1f,0/pci@1
/pci@1f,0/pci@1,1
/pci@1f,0/pci@1/pci@1
/pci@1f,0/pci@1/pci@1/SUNW,qfe@3,1
/pci@1f,0/pci@1/pci@1/pci108e,1000@3
/pci@1f,0/pci@1/pci@1/SUNW,qfe@2,1
/pci@1f,0/pci@1/pci@1/pci108e,1000@2
/pci@1f,0/pci@1/pci@1/SUNW,qfe@1,1
/pci@1f,0/pci@1/pci@1/pci108e,1000@1
/pci@1f,0/pci@1/pci@1/SUNW,qfe@0,1
/pci@1f,0/pci@1/pci@1/pci108e,1000@0
/pci@1f,0/pci@1,1/ide@3
/pci@1f,0/pci@1,1/SUNW,m64B@2

Commands that are used to examine the device tree:

Command	Description
`.properties`	Displays the names and values of the current node's properties.
`dev <device-path>`	Chooses the specified device node and makes it the current node.
`dev <node-name>`	Searches for a node with the specified name in the subtree below the current node and chooses the first such node found.
`dev ..`	Chooses the device node that is the parent of the current node.
`dev /`	Chooses the root machine node.
`device-end`	Leaves the device tree.
`<device-path> find-device`	Chooses the specified device node, similar to `dev`.
`ls`	Displays the names of the current node's children.
`pwd`	Displays the device pathname that names the current node.
`see <wordname>`	Decompiles the specified word.
`show-devs <device-path>`	Displays all the devices known to the system directly beneath a given device in the device hierarchy. `show-devs` used by itself shows the entire device tree.
`words`	Displays the names of the current node's methods.
`<device-path>" select-dev`	Selects the specified device and makes it the active node.

You can examine the device path from a Unix shell prompt by typing the following:

prtconf –vp

OpenBoot Device Aliases

Create and remove custom device aliases.

Device pathnames can be long and complex. Device aliases, like Unix aliases, allow you to substitute a short name for a long name. An alias represents an entire device pathname, not a component of it. For example, the alias disk0 might represent the following device pathname:

/sbus@1,f8000000/esp@0,40000/sd@3,0:a

OpenBoot provides the predefined device aliases listed in Table 3.5 for commonly used devices, so you rarely need to type a full device pathname. Be aware, however, that device aliases and pathnames can vary on each platform. The device aliases shown in Table 3.5 are from a Sun Ultra 5 system.

Predefined Device Aliases

Alias	Device Pathname
`disk`	`/pci@1f,0/pci@1,1/ide@3/disk@0,0`
`disk0`	`/pci@1f,0/pci@1,1/ide@3/disk@0,0`
`disk1`	`/pci@1f,0/pci@1,1/ide@3/disk@1,0`
`disk2`	`/pci@1f,0/pci@1,1/ide@3/disk@2,0`
`disk3`	`/pci@1f,0/pci@1,1/ide@3/disk@3,0`
`cdrom`	`/pci@1f,0/pci@1,1/ide@3/cdrom@2,0:f`

If you add disk drives or change the target of the startup drive, you might need to modify these device aliases. Table 3.6 describes the devalias commands, which are used to examine, create, and change OpenBoot aliases.

NOTE

New Names Overwrite Old Names If an alias with the same name already exists, the new value overwrites the old.

Table 3.6 - The `devalias` Commands

Command	Description
`devalias`	Displays all current device aliases
`devalias` `<alias>`	Displays the device pathname that corresponds to `alias`
`devalias_alias <device-path>`	Defines an alias that represents `device-path`

The following example creates a device alias named disk3, which represents an Integrated Drive Electronics (IDE) disk with a target ID of 3 on an Ultra 5 system:

devalias disk3 /pci@1f,0/pci@1,1/ide@3/disk@3,0

To confirm the alias, you type devalias, as follows:

ok devalias

The system responds by printing all the aliases, like this:

screen          /pci@1f,0/pci@1,1/SUNW,m64B@2

net           /pci@1f,0/pci@1,1/network@1,1

cdrom          /pci@1f,0/pci@1,1/ide@3/cdrom@2,0:f

disk           /pci@1f,0/pci@1,1/ide@3/disk@0,0

disk3          /pci@1f,0/pci@1,1/ide@3/disk@3,0

disk2          /pci@1f,0/pci@1,1/ide@3/disk@2,0

disk1          /pci@1f,0/pci@1,1/ide@3/disk@1,0

disk0          /pci@1f,0/pci@1,1/ide@3/disk@0,0

ide           /pci@1f,0/pci@1,1/ide@3

floppy          /pci@1f,0/pci@1,1/ebus@1/fdthree

ttyb           /pci@1f,0/pci@1,1/ebus@1/se:b

ttya           /pci@1f,0/pci@1,1/ebus@1/se:a

keyboard!        /pci@1f,0/pci@1,1/ebus@1/su@14,3083f8:forcemode

keyboard         /pci@1f,0/pci@1,1/ebus@1/su@14,3083f8

mouse          /pci@1f,0/pci@1,1/ebus@1/su@14,3062f8

name           aliases

You can also view device aliases from a shell prompt by using the prtconf –vp command.

User-defined aliases are lost after a system reset or power cycle unless you create a permanent alias. If you want to create permanent aliases, you can either manually store the devalias command in a portion of NVRAM called NVRAMRC or you can use the nvalias and nvunalias commands. The following section describes how to configure permanent settings in the NVRAM on a Sun system.

OpenBoot NVRAM

List, change, and restore default NVRAM parameters.
View and change NVRAM parameters from the shell.

System configuration variables are stored in system NVRAM. These OpenBoot variables determine the startup machine configuration and related communication characteristics. If you modify the values of the configuration variables, any changes you make remain in effect even after a power cycle. Configuration variables should be adjusted cautiously, however, because incorrect settings can prevent a system from booting.

Table 3.7 describes OpenBoot's NVRAM configuration variables, their default values, and their functions.

NVRAM Variables

Variable	Default	Description
`auto-boot?`	`true`	The system starts up automatically after power-on or reset if `auto-boot?` is `true`. If it is set to false, the system stops at the OpenBoot prompt (`ok`) after power-on or reset.
`boot-command`	`boot`	The command that is executed if `auto-boot?` is `true`.
`boot-device`	`disk` or `net`	The device from which to start up.
`boot-file`	Empty string	Arguments passed to the started program.
`diag-device`	`net`	The diagnostic startup source device.
`diag-file`	Empty string	Arguments passed to the startup program in diagnostic mode.
`diag-switch?`	`false`	Whether to run in diagnostic mode.
`fcode-debug?`	`false`	Whether name fields are included for plug-in device FCodes.
`input-device`	`keyboard`	A console input device (usually `keyboard`, `ttya`, or `ttyb`).
`nvramrc`	Empty	The contents of NVRAMRC.
`oem-banner`	Empty string	A custom original equipment manufacturer (OEM) banner (enabled with `oem-banner? true`).
`oem-banner?`	`false`	If `true`, use custom OEM banner.
`oem-logo`	No default	A byte array custom OEM logo (enabled with `oem-logo? true`). Displayed in hexadecimal.
`oem-logo?`	`false`	If `true`, use custom OEM logo; otherwise, use the Sun logo.
`output-device`	`screen`	A console output device (usually `screen`, `ttya`, or `ttyb`).
`sbus-probe-list`	`0123`	Which SBus slots to probe and in what order.
`screen-#columns`	`80`	The number of onscreen columns (characters/line).
`screen-#rows`	`34`	The number of onscreen rows (lines).
`security-#badlogins`	No default	The number of incorrect security password attempts.
`security-mode`	`none`	The firmware security level (options: `none`, `command`, or `full`).
`security-password`	No default	The firmware security password (which is never displayed).
`use-nvramrc?`	`false`	If `true`, execute commands in NVRAMRC during system startup.

NOTE

OpenBoot Versions Because older SPARC systems use older versions of OpenBoot, they might use different defaults or different configuration variables from those shown in Table 3.7. This text describes OpenBoot version 4.

You can view and change the NVRAM configuration variables by using the commands listed in Table 3.8.

Table 3.8 - Commands for Viewing and Modifying Configuration Variables

Command	Description
`password`	Sets the security password.
`printenv`	Displays the current value and the default value for each variable. To show the current value of a named variable, you type the following: `printenv <parameter-name>`
`setenv <variable> <value>`	Sets `<variable>` to the given decimal or text `<value>`. Changes are permanent, but they often take effect only after a reset.
`set-default <variable>`	Resets the value of `<variable>` to the factory default.
`set-defaults`	Resets variable values to the factory defaults.

The following examples illustrate the use of the commands described in Table 3.8. All commands are entered at the ok OpenBoot prompt.

You use the printenv command, with no argument, to display the current value and the default value for each variable:

ok printenv