MPE/iX System Utilities Reference Manual > Chapter 25 STANDARDS

The initial system loader

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The Initial System Loader performs these functions:

provides user interface with boot path information and alters boot path.
loads an operating system-specific code set or a hardware-specific code set and launches it. If this implementation-specific code does not damage the ISL image, ISL remains in memory in case the code returns control to ISL for initialization of further utilities.

Certain standards are used by hardware and software operating systems using system bootstrap, IPL, and ISL standard. These standards are architectural in nature, but are not necessarily defined in any system architectural document. The remainer of this chapter contains a description of these standards.

Stable storage and nonvolatile memory layout

Stable storage and nonvolatile memory (NVM) are described as blocks of bytes that are accessible by bootstrap, ISL, and the operating system through standard entry points. The first 96 bytes of stable storage are required implementation; bytes 96 through 191 are optional, but if implemented they are reserved for PDC and ISL access as described below. Nonvolatile memory is not required by the architecture; therefore, it should contain only values that can be managed by an alternate method. When more than one byte is used in the representation of an item in stable storage, the most significant byte is the byte with the lower address.

The format of stable storage is shown below:

Table 25-1 Stable storage format

BYTE	CONTENTS
0-31	Boot flags and device
32-63	Unique file names
64-95	Future OS requirements
96-127	Console terminal
128-159	Alternate boot path
160-191	Dump flags and device
192-`nnn`	Future OS options

Autoboot flags and device path

This 32-byte field defines the coldload path that PDC uses for autoboot. If this path is not valid, or if the device that it describes is not a valid boot device containing an IPL image, PDC then requests a valid path through the console if the console is present; otherwise, the error is displayed through the front panel.

A detailed internal representation of a boot or console path (the format applies to the auto bootpath, the alternate boot path, the dump path, and the console path) is as follows:

Table 25-2 Boot or console path

0000	flags	BC(0)	BC(1)	BC(2)
0004	BC(3)	BC(4)	BC(5)	MOD
0008		Logical_ID
000C		Device_Depend
001F
0020

Note that in the above illustration, the flags field in the console path is ignored. The format of flags is as follows:

Format of flags

Table 25-3 Format of flags

0	1	2-3	4 through 7
ab	as	00	timer

Console Path

This 32-byte field defines the device path that PDC uses to locate the system console. If this path is not valid, or if the device that it describes is not a valid console device image, PDC then uses a default path.

Alternate Boot Path

This 32-byte field defines the coldload path that PDC uses (after getting the go-ahead from the operator) if the operator rejects the autoboot path through console intervention. If this path is not valid, or if the device it describes is not a valid boot device containing an IPL image, PDC then requests a valid path through the console.

Dump flags and device

This 32-byte field is used to describe the destination device for a snapshot dump facility.

The format of nonvolatile memory is shown below:

Table 25-4 Nonvolatile memory

BYTE	CONTENTS
0-63	PDC and boot reserved
64-nn	OS reserved

NVM is an optional implementation, not required by the architecture. If NVM is implemented, the PDC and boot reserved area of NVM is as follows:

Table 25-5 PDC and boot area for NVM

BYTE	CONTENTS
0-1F	Last boot-device path
20-23	Self-test status
24-27	Powerfail time stamp
28-2A	Boot restart time stamp
2B-2F	TOC restart time stamp
30-63	PDC and boot reserved

LIF standard

The Hewlett-Packard Logical Interchange Format (LIF) provides a standard method for locating IPL code on the boot device.

The method of locating IPL code on the boot device must be the same for all boot devices, computer processors, and the operating systems, so that the PDC knows where to find it. Having IPL at the very beginning of the device is ideal; however, some operating systems require a volume label at the beginning of a disk. IPL also needs a method of locating its modules (utilities) when they are needed.

The LIF standard addresses these issues, and provides a standard with utilities already in existence. For further information on LIF format, refer to LIF Directory Organization and Record Format for Data Interchange.

LIF requires a 256-byte volume label at the beginning of the media; thus, the operating-system-specific volume label can be located at the beginning of the disk, offset by 256 bytes. The LIF volume label points to the location of the LIF directory, which then points to the location of each of the files.

Compliance to LIF standard does not require complete implementation. The level of compliance to the standard in the IPL code is the minimum implementation (volume header and directory in ASCII code). The format of the files is the system object module (SOM) format.

The LIF volume header, as well as an entry in the LIF directory, points to the IPL code.

The following drawing represents the LIF standard logical layout of disk and tape media.

Figure 25-1 LIF Standard Logical Layout

The LIF volume label allows easy identification of media type and gives the location of the directory. The format of the LIF volume label follows:

Table 25-6 LIF volume label format

BYTE	CONTENTS
0-1	LIF identifier
2-7	Volume label (0-6 ASCII characters)
8-11	Directory start address (in blocks)
12-13	Octal 10000
14-15	Set to 0 (dummy)
16-19	Length of directory (fixed at initialization)
20-21	Set to 0
22-23	Set to 0
24-41	Set to 0 (level 1 extension)
42-239	Set to 0 (reserved for extensions and future use)
240-243	Byte address of IPL on media
244-247	IPL length (in bytes)
248-251	Offset in IPL of entry
252-253	Set to 0
254-255	Set to 0 (reserved by system 250)

The directory contains all of the information necessary to find files. It is a linear list of 32-byte directory entries, one for each LIF file on the media. The maximum number of entries in the directory is fixed at the time of initialization. A logical end of directory mark is defined to be a file type of -1 and is written only if the directory is not filled. The physical end of directory is determined by adding the start of directory and length of directory fields from the volume lable. Directory entries must be stored so that they are in strictly increasing starting addresses on sequential media. Directory entries are undefined after the logical end of directory, so when a file is appended to the directory, the following directory entry's file type must be set to -1 to make it the logical end of the directory.

LIF addressing is in blocks of 256 bytes, and system addresses are 2K-bytes-aligned.

Each directory is organized as follows:

Table 25-7 LIF addressing

BYTE	CONTENTS
0-9	File name (1-10 ASCII characters, trailing blanks)
10-11	File type
12-15	Starting address (in blocks)
16-19	Length of file (in blocks)
20-25	Time of creation
26-27	1 /volume number
28-31	Set to 0 (implementation)

The file type is a 16-bit signed integer. The defined file types that are recognized by systems are

0 -- Purged file
30001 -- Bootable, executable file
30002 -- Boot data file
30003 -- Autoexecutable file list
30004 -- Data protect file
30010 -- HPE system file

A file is deleted from the directory by changing its file type to -2, to represent a purged file. The data itself need not be removed from the media.

Bootable utility format

All of the bootable utilities accessible through the LIF directory must have enough of a common format for IPL to load and launch the utilities through a standard method. IPL may need to know the intended physical memory destination address for which the module was linked, as well as the length of the image and the entry point. For those utilities that are position independent, the destination address can be set to -1 and IPL will load it at the first available memory after IPL.

All software implementation intends to support the system object module (SOM) format, using the linker; therefore, an auxilary SOM header for IPL, as described below, would meet IPL's needs for loading and launching bootable utilities. For further description of the linker and the SOM format, refer to the System Linker External Specifications and the System Object File Format Architectural Control Document.

Figure 25-2 Boot utility format

Main Memory Layout

Although the exact memory locations of boot and IPL code during the boot process vary according to size of the IODC and IPL, a general description of memory layout is presented here for clarification. Also, the first page of main memory is reserved for communication between PDC and software.

Table 25-8 Main memory layout

X'00000000	Initalize vectors	0
X'00000040	Processor dependent	64
X'00000200	Reserved	512
X'00000350	Memory configuration	848
X'00000360	MEM_ERR	864
X'00000380	MEM_FREE	896
X'00000384	MEM_HPA	900
X'00000388	MEMPDC	904
X'0000038C	MEM_10MSEC	908
X'00000390	Initial memory module	912
X'000003A0	Boot console/display	928
X'000003D0	Boot device	976
X'00000400	Boot keyboard	1024
X'00000430	Reserved	1072
X'00000600	Processor dependent	1536
X'00000800		2048

The format of the first memory controller configuration is as follows:

word0: HPA of the memory controller
word1: SPA of the corresponding memory
word2: SPA_size
word3: Max_Mem

The format of the console terminal and boot device configurations are as follows:

Table 25-9 Console terminal and boot device configuration

X'00	path	00
X'08	LAYERS	08
X'20	HPA	322
X'24	SPA	36
X'28	IODC_IO	40
X'2C	Reserved	44
X'30	Class	48

The format of the boot and system console device paths is the same as that for the autoboot, alternate boot, and console paths in stable storage. In the console path, the flags are ignored.

The offsets of IODC, IPL, and booted utilities are variable, based on the size of code images.

Table 25-10 IODC, IPL, and booted utilities offsets

X'00000000	Page zero	0
X'00000800		2048
MEM_FREE	Monarch PDC	MEM_FREE
	Console IODC
	Boot Device IODC
IPL_START	IPL code	IPL_START

The bootstrap

Chapter 26 SYSMAP

The initial system loader

MPE documents

Stable storage and nonvolatile memory layout

LIF standard

Bootable utility format