System Initialization - ZiLOG Z80-RIO Operating System User's Manual

1.2.3 SYSTEM INITIALIZATION
Where ZDOS is the primary file system, the bootstrapping
of the operating system is from floppy disks. When a
carriage return is entered as the first character after
pressing RESET, or when the OS command is entered while
in the Debug environment, the PROM monitor reads a 128 byte
minibootstrap from track 17, sector 3 of the disk in drive
O.
This program initiates a directory search on drive 0 for
the files OS and ZDOS, which are then read into memory.
Execution is started at the entry point of
as.
This is
one of two instances where a disk formatted as a system
disk must be ready in drive
O.
The other is when using the
GET or SAVE commands of the PROM Debugger. In all other
cases, while a particular drive search order may be implied,
there is no difference in the utilization of drives.
This process is similar on systems which use DFS as the
primary file system. The file 'BOOTSTRAP' contains the
file system, which the disk controller loads directly
from disk, using the standard disk search sequence of
drive 1, drive 2, ... , drive
O.
The PROM monitor then may
communicate directly with the controller to load the file
'OS', again using the standard drive search sequence.
When execution of the file
as
begins, an initialization
procedure is performed that mayor may not involve other
files. A means is provided to read a set of commands from
a file to extend this initialization process. In this way,
a turnkey system can be implemented simply by editing the
external initialization command file. Alternatively, the
file
as
can be edited directly to execute a user-defined
command sequence at initialization time (see Appendix E). As
part of the initialization process, memory is sized to determine
the current configuration. If the sizing
procedur~
determines
the end of memory to be at other than a 4K boundary, a
warning message is issued to indicate possible memory
failure, thus providing a frequent diagnostic of system
memory.
After initialization, OS responds with the message 'RIO REL v.cc
(Where 'v' is the release version and
ICC'
is the release cycle)
followed by the system prompt character '%'. Any time RIO
is ready to accept command input, this prompt character is
printed.
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