ERPFX$ 1R1D - ER PFx$ to BSP$ Redirection

ERPFX$ 1R1D - ER PFx$ to BSP$ Redirection

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1. Introduction

ERPFX$ is a library routine that allows programs using PFx$ Executive Requests (PFWL$, PFS$, PFI$, PFD$, PFUWL$) to be redirected to the SYSLIB routine BSP$ with little modification, thus allowing full support for LPF and LEPF files. The ERs are intercepted and converted to subroutine calls; program files are read and updated as needed transparently to the user; and status registers are returned as with the actual ERs. Provisions are made for banking most of the IBANK and DBANK portions of ERPFX$ so that there will be little size increase to the program.

ERPFX$ consists of the omnibus definition element ERPFX$DEF and the relocatable element ERPFX$/nRnx, which must be available at compile and @MAP time, respectively.

2. Implementation [Top][Contents]

For a program to use ERPFX$, the following statement must appear at the beginning of every element containing an ER PFx$ call; it may follow other standard $INCLUDEs:

        $INCLUDE  'ERPFX$DEF'

In addition, the following procedure call -- which also needs the above $INCLUDE -- must appear somewhere in the program, preferably in the main data area, although the proc will always revert to the location counter in effect on entry after generating its data.

        ERPFX$SETUP[,'CB']  [Nfiles,Ntrks,RtnReg]  [MainLC,BulkLC,BulkBDR]

where:

'CB' - If present, calls to BSP$ routines are common banked vs. relocatable. If 'CB' is used, the program must follow the convention that all data to be accessed by BSP$ must be based and above 040000 when BSP$ is called; and only the main IBANK and other unbased IBANKs may overlap it from 01000-040000.

Nfiles - The maximum number of files for which ER PFx$ calls are processed. Default: 2. The PFx$ ERs only deal with internal filenames which are assumed to be assigned, so this number represents the number of distinct internal filenames to be used with ERPFX$.

Ntrks - The number of memory tracks (1792 words each) to reserve for each file's element table, in addition to the pointer table. Default: 1.

Because BSP$ deals with the element table in pages, the default size is enough to handle any size program file and there is no danger of overflow. However, increasing Ntrks can improve efficiency.

RtnReg - If present, the register to use when returning from ERPFX$. This is only required if multiple activities in the program will perform ER PFx$s. RtnReg may be X1-X11, A0, or A3. (A1 and A2 are used to return information and status.)

If omitted, ERPFX$ will return using an indirect jump. ERPFX$ performs all its functions with the data area locked out, but it must unlock it just before the return, which could leave a small window if multiple activities are involved; hence the need for RtnReg.

MainLC - The location counter under which to generate the program's basic data area for ERPFX$ interface, about 33 words. Default: 60.

This location counter must be collected so as to be based whenever an ER PFx$ is performed, and must be located under the 65K (200000 octal) boundary.

BulkLC - The location counter under which to generate the bulk of the data used for ERPFX$ and BSP$ interface. Default: 62. This area's size is 23+Nfiles*(Ntrks*1792+196) words and includes each file's FCT, FTI, and element table area.

This location counter may be placed either in the program's main DBANK, if there is room, or in a parallel DBANK starting at the same address. ERPFX$ will switch banks as needed, since this area must be based and available whenever BSP$ is called. It must also be based simultaneously with ERPFX$'s $(3), whether in the same or a different bank. It may be located above the 65K (200000 octal) boundary.

BulkBDR - If present, the BDR on which to base the bulk data for ERPFX$. Default: 2 (Main DBANK). This is intended for the case where the bulk data is in an unbased bank parallel to some other bank that is based on a BDR other than the main DBANK at the time of the call. If BulkBDR is -1, this will signal ERPFX$ to obtain the BDR for the bulk data from the value coded in the second subfield of the second field of the DBANK statement for this bank,

Example: 'DBANK PFXDBANK ,3'

The relocatable element ERPFX$/nRnx must be LIB'd or explicitly collected with the program. It has two IBANK location counters: $(1) (21 words), which must be collected so as to be based at the time of the call, preferably in the main IBANK; and $(3) (194 words), which may be in the same or a different bank and need not be based at the time of call. If based, however, it must not displace either of ERPFX$'s data areas, or any data which may be passed to BSP$, namely the PFS$ packet. ERPFX$ will base this bank as needed, using the main IBANK BDR by default unless an alternate BDR is coded in the second subfield of the second field of the bank's IBANK statement.

Example: 'IBANK PFXIBANK ,1'

If BSP$ is called as a relocatable as opposed to a common bank, its instruction and data areas must both be based at the time ERPFX$ calls it, which means at the time $(3) of ERPFX$ is based. This may mean collecting its odd and even location counters in the same bank as $(3) of ERPFX$, or in one or two banks that will be based at the time $(3) of ERPFX$ is based.

The sequence below illustrates which IBANK and DBANK areas need to be based at the same time during the steps of a typical call to ERPFX$:

   1. ERPFX$($1) - MainLC - User's PFS$ packet
   2. ERPFX$($3) - MainLC - User's PFS$ packet
   3. ERPFX$($3) - BulkLC
   4. BSP$       - BulkLC
   5. ERPFX$($3) - BulkLC
   6. ERPFX$($3) - MainLC - User's PFS$ packet
   7. ERPFX$($1) - MainLC - User's PFS$ packet

3. Operation [Top][Contents]

The following is a description of the default operation of each intercepted PFx$ ER. In all cases, A0 is loaded with the address of the program file packet: a two-word internal filename, usually followed by a 6- or 10-word element entry. (Each LA A0 instruction in the descriptions shows how many words are expected.) In two cases A1 is loaded with an updated write location.

3.1. PFWL$ - Obtain Next Write Location [Top][Contents]

        LA,U A0,PFPKT       . (2)
        ER   PFWL$