Program Logic Manual - All about the IBM 1130 Computing System

prior to performing any disk operations, and intolocations $DCYL through $DCYL+2 in the ResidentImage.The fourth word of the sector (the cartridgeidentification word, initialized by the DCIP or DISCprogram) is placed into location #CIDN in DCOM.The seventh word of the sector is the cartridgeload status word. Minus 2 indicates that an initializationhas been performed and an initial load only ispermitted. Plus 2 indicates that the cartridge hasbeen initial-loaded and a reload only is permitted.SYSTEM LOCATION EQUIVALENCE TABLE (SLET)SLET occupies three adjacent sectors on the systemcartridge. Its functions are:• To provide a convenient means for locating eachmonitor system program that has been stored onthe system cartridge.• To indicate which are the principal I/0 devicesfor the system.• To indicate which devices, if any, are not presenton the system.When the System Loader initially stores a phaseof a monitor system program on the disk, it makesa 4-word entry in SLET for that program consistingof:1. The phase identification (phase ID) number.2. The core loading address of the phase. This isthe address in which the word count is to bestored prior to fetching the phase from the disk.3. The word count of the phase, not including thetwo words occupied by the word count and sectoraddress used in fetching the phase from disk.4. The sector address of the phase.During an initial load, the SLET sectors arecleared to zero. The 4-word entries describingeach phase are built into the table, phase by phase,as the monitor system programs are loaded. (Aprogram or phase not included during an initial loadcannot later be included in a reload operation unlessthe program to be reloaded meets the requirementsdescribed under FUNCTIONS, RELOAD ONLY.Otherwise a new initial load must be performed.)All phase ID numbers in SLET are in ascendingorder. No duplications exist. The only jumps insequence are between programs, not between phaseswithin a nroaram.The five 4-word entries describing the principalI/O devices and the corresponding conversion subroutinesare built by the System Loader and do notcome directly from program decks.The contents of SLET can be obtained at any timeby an execution of the DSLET program (see thedescription of DSLET under Mainline Programsin Section 12. System Library).RELOAD TABLEThe Reload Table occupies one sector on the systemcartridge. It contains a 3-word entry for each phasethat requests SLET information. Word 1 of eachentry contains the phase ID number of the requestingphase. Word 2 of each entry contains the address ofthe location, relative to the beginning of the phase,where the SLET entries are to be inserted into therequesting phase. Word 3 of each entry contains thenumber of 4-word SLET entries to be inserted intothe requesting phase. The phase ID number of therequesting phase itself is in 2's complement formto indicate to the System Loader that SLET data isrequested by that phase.When completed at the end of an initial load orreload operation, the Reload Table consists of astring of 3-word entries, as described above, exceptthat the phase ID numbers have been recomplementedby the System Loader. At the end of the string is/FFFF. It may be at an odd or an even address,depending upon the length of the string. The lestword of the Reload Table is used for the SLET andReload Table checksum. At the end of an initialload, the phase ID numbers are in ascending order.After one or more reload operations the phase IDnumbers may or may not be in ascending order.When a DEFINE VOID ASSEMBLER or DEFINEVOID FORTRAN operation is performed by DUP,all phase ID numbers belonging to the voided program(s)are removed from the Reload Table. Theremaining 3-word entries in the Reload Table arepacked together and terminated with /FFFF.14