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

0000flagsBC(0)BC(1)BC(2)
0004BC(3)BC(4)BC(5)MOD
0008Logical_ID
000CDevice_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

012-34 through 7
abas00timer

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
0-63PDC and boot reserved
64-nnOS 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
0-1FLast boot-device path
20-23Self-test status
24-27Powerfail time stamp
28-2ABoot restart time stamp
2B-2FTOC restart time stamp
30-63PDC 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

[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
0-1LIF identifier
2-7Volume label (0-6 ASCII characters)
8-11Directory start address (in blocks)
12-13Octal 10000
14-15Set to 0 (dummy)
16-19Length of directory (fixed at initialization)
20-21Set to 0
22-23Set to 0
24-41Set to 0 (level 1 extension)
42-239Set to 0 (reserved for extensions and future use)
240-243Byte address of IPL on media
244-247IPL length (in bytes)
248-251Offset in IPL of entry
252-253Set to 0
254-255Set 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
0-9File name (1-10 ASCII characters, trailing blanks)
10-11File type
12-15Starting address (in blocks)
16-19Length of file (in blocks)
20-25Time of creation
26-271 /volume number
28-31Set 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

[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'00000000Initalize vectors0
X'00000040Processor dependent64
X'00000200Reserved512
X'00000350Memory configuration848
X'00000360MEM_ERR864
X'00000380MEM_FREE896
X'00000384MEM_HPA900
X'00000388MEMPDC904
X'0000038CMEM_10MSEC908
X'00000390Initial memory module912
X'000003A0Boot console/display928
X'000003D0Boot device976
X'00000400Boot keyboard1024
X'00000430Reserved1072
X'00000600Processor dependent1536
X'000008002048

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'00path00
X'08LAYERS08
X'20HPA322
X'24SPA36
X'28IODC_IO40
X'2CReserved44
X'30Class48

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'00000000Page zero0
X'000008002048
MEM_FREEMonarch PDCMEM_FREE
Console IODC
Boot Device IODC
IPL_STARTIPL codeIPL_START



The bootstrap

Chapter 26 SYSMAP