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BSP$-Program File Basic Service Package
Some guidelines concerning the use of BSP$ are the following:
• There are two basic program file formats. The standard program file (PF) has small
variable-length tables. The large program file (LPF) has large fixed-length tables. For
example, the PF has a normal maximum of 2,671 element table entries that can be
expanded to 5,000 entries, while the LPF has a fixed maximum of 26,146 element
table entries.
• PF and LPF elements are limited to a maximum of 262,143 sectors of text for each
element. A new program file type, the large element program file (LEPF) removes
this limitation and allows elements to have over 262,143 sectors of text, if desired.
An LEPF can be initialized with the small variable-length format of a standard
program file (standard LEPF) or with the large fixed-length format of a large program
file (large LEPF).
• If the calling program attempts to create a program file in a file area in which a file
was previously written, the calling program will receive an error return if the first
word encountered is not the program file identifier constant or if sector 0 is not all
zeros.
• For standard PF format, each table on mass storage begins at the system-defined
sector or at a greater sector if a previous table occupies the defined sector. The
element table always starts at the system-defined sector. The system-defined
sectors and starting sector for element text are the six ‘PFxx$' equates in element
SYS$DEF (see Table 2–4).
• For LPF formats, each table on mass storage begins at the system-defined sector.
The system-defined sectors and starting sector for element text are the six 'LPF$xx'
equates in element SYS$DEF (see Table 2–4).
• For standard PF formats, the system default TOC size is 1,792 sectors (28 tracks).
For LPF formats, the system default TOC size is 40,256 sectors (629 tracks).
• The calling program must provide a 43-word data area (for BSP$). This area is
referred to as the file control table (FCT). The calling program must also provide
main storage buffers for each table read.
• The calling program must request to read the FTI before any other BSP$ functions
are called. The FTI must be in the BSP$ FCT until all BSP$ functions are executed.
• The FTI part of the FCT data area is used by BSP$ to contain necessary information
about the file.
• A table must be read into the caller’s buffer (RPFxxT$ calls) before any operations
are performed on the table.
• BSP$ returns an error code if a table cannot hold another item.
• A table must be written back from the caller's buffer (WPFxxT$ calls) before the
buffer can be used to hold another table.
• BSP$ operates most efficiently when the caller’s buffer is large enough to contain
the entire program file table, including the size of entries to be added to the table.
The current length of each program file is available when the FTI is read.
• Each table that has been modified must be written back to the program file table of
contents on mass storage.
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