DESCRIPTION
pdc
is the firmware that implements all processor-dependent functionality,
including initialization and self-test of the processor.
Upon completion, it loads and transfers control
to the initial system loader
(isl(1M)).
Firmware behavior varies somewhat, depending on the hardware
as described below.
To load
isl
from an external medium,
pdc
must know the particular device on which
isl
resides.
Typically the device is identified by the Primary Boot Path
that is maintained by
pdc
in Stable Storage.
A
path
specification is an
I/O
subsystem mnemonic that varies according to hardware model.
When the processor is reset after initialization and self-test complete,
pdc
reads the Console Path from Stable Storage,
and attempts to initialize the console device.
If the initialization fails,
pdc
attempts to find and initialize a console device.
Algorithms used to find a console device are model-dependent.
pdc
then announces the Primary Boot, Alternate Boot, and Console Paths.
If
autoboot
(see
isl(1M))
is enabled,
pdc
provides a 10-second delay,
during which time the operator can override the
autoboot
sequence by typing any character on the console.
If the operator does not interrupt this process,
pdc
initializes and reads
isl
from the Primary Boot Path.
On models that support autosearch, if this path is not valid and
autosearch
(see
isl(1M))
is enabled,
pdc
then searches
to find a bootable medium.
If allowed to complete, a list of potentially bootable devices
is displayed, labeled with abbreviated path identifiers
(P0, P1, etc).
A simple menu is then displayed where the user can:
Boot a specific device, using the abbreviated path
identifier, or the full mnemonic.
Start a device search where the contents are searched for
IPL
images (note the first search only identified devices
and did not check the contents).
Enter the boot administration level.
Exit the menu and return to autobooting
If the
autoboot
sequence is unsuccessful, overridden by the operator,
or not enabled in the first place,
pdc
interactively prompts the operator for the Boot Path to use.
Any required path components that are not supplied default to zero.
The Primary Boot, Alternate Boot, and Console Paths as well as
autoboot
and
autosearch
enable can be modified via
isl.
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