MOD1 MSR Operating System Implementation

An implementation/simulation of the MOD1 MSR (Mass Storage Resident) operating system and programming environment is available. This provides an easy way to manipulate files on mass storage media (Disk Packs). This feature is implemented as a set of java virtual extensions. See Virtual Series 2000 Extensions for more on virtual software extensions.

Features of "File Support C" and "Volume Preparation C" are implemented in the menu "Disk Util". These allow initialization of a volume, mapping (listing) of a volume, and allocation (create) and deallocation (delete) of files. See information in Basic Operation.

Access to files (data) in programs is through the MOD1MSIO virtual macros package, invoked (loaded) using the "MAC" assembler directive as described in Easycoder Assembler Implementation. Apart from the non-standard virtual extension "MAC", the macros are used as described in the original MOD1 documentation, with the following exceptions:

• Only Sequential and Partitioned Sequential Organization files are supported.
• Only single-volume files are supported.
• Password protection is not Supported.
• The MUCA and MLCA macros are not fully supported.
• Cylinder and general overflow is not Supported.
• File data type designation (print-image, etc) is not Supported.
• Some advisory EXITs are not supported.
• more...?

Here is a sample program to read a file named "MYFILE01" and print it, simplified for clarity.

00010* MOD1 PROGRAM TO TEST READING DISK FILE
00020         PROG  MOD1T2
00030         ORG   1340
00040         ADMODE4
00050         MAC   MOD1MSIO
00060*
00070L        MIOC  A
00080*
00090C F1     MCA   A,DEVTAB
00100C        10    RECD2,,MOVE,RECD1
00110C        20    MYFILE01,
00120C        31    00,
00140L        43    DEXIT,
00170*
00180  START  CAM   60
00190L        MSOPENF1,IN
00200L NEXT   MSGET F1,
00210         PDT   RECD1,12,02,01    PRINT RECORD
00220         PCB   *,12,02,00
00230         B     NEXT
00240*
00250L DONE   MSCLOSF1,
00260         PDT   FIN,10,02,01
00270         PCB   *,10,02,00
00280         B     (164)             MOD1 PROGRAM EXIT
00290*
00300  ABORT  DCW   #1C40
00310  DEXITC DCW   #1B0
00320  DEXIT  SCR   DXITZ,70
00330         BCE   DONE,DEXITC,01    EOF IS SOFT ERROR
00340         EXM   ABORT,VEXITC,01   ANYTHING ELSE FATAL
00350   DXITZ B     0
00360*
00410  DEVTAB RESV  0
00420         DCW   #3C040000         PCU, LUN, 00
00430 L       DCW   #1B0
00440*
00450   RECD1 RESV, 80                ITEM BUFFER
00460 L       DCW   #1A
00470*
00480   RECD2 RESV, 256               BLOCK BUFFER
00490 L       DCW   #1A
00500 L       DCW   #1A
00510 L       DCW   #1A
00520*
00530 F FIN   DC    @FINISHED @
00540*
00550         END   START

At card (line) 00050 is the modern (non-standard) extension to EasyCoder to load a macro library.

At line 00070 is the initialization of MIOC, declaring instance "A". Note that, in this implementation, all of MIOC/MPIOC is in a virtual runtime and thus consumes no extra program memory, making most parameters to MIOC irrelevant.

Beginning at line 00090 is the definition of the MCA for "MYFILE01".

At line 00190 the file is opened for input-only. Note, any failures at this point cause an EXIT call which is fatal/terminal.

At line 00200 one item is read from the file. Note, a Data EXIT for EOF will cause a graceful end to the program, checked on line 00330.

In the case of a graceful end, the file is closed on line 00250.

System Files

All of these system files are Partitioned Sequential files. Currently, "*DRS1LIB" is not used (native macros not yet supported). "*DRS1GO" is the default output file for the "Disk Image" option of the assembler. "*DRS1RES" is the only input for MOD1 executables. Executables are managed using the menu option "Executable Function" under "Disk Util".

File Name	Purpose	Item, Record, Block length
*DRS1RES	Resident Executable Images	250, 250, 250
*DRS1GO	Assembler Output Executables	250, 250, 250
*DRS1LIB	Unspecialized Macros	80, 250, 250

Bootstrap

When booting, this code expects a partitioned-sequential file name "*DRS1RES" that contains an executable program image in the member named "SUPER101" (visibility is not checked). This program will be loaded and executed whenever the code boots or is entered again ("normal program exit"). If SUPER1 is made resident, then it should intercept the entry calls and prevent mod1loader from redundantly loading SUPER1.

The code for SUPER1 is in superv.ezc, and may be assembled using the built-in H2000 Assemble function, with the "Disk Image" option (if "*DRS1RES" exists). The "*DRS1RES" file may be created on any volume using the "Allocate File" function. The file must have a item, record, and block size of 250 and an index size (and data allocation) sufficient for storing the desired set of programs.

SUPER1 (as implemented by superv.ezc) will print READY on the console typewriter and wait for a 6-character command. The command must be either "EXΔΔΔΔ" or "TESTΔΔ". After entering the 6th character, enter one more space to confirm the command or any other character to abort and return to READY. If the command is not recognized, "WHAT?" will be printed. After the command is accepted, enter the 8 character program and segment name of a program on the resident ("EX") or go ("TEST") file, then press RETURN. If the program can be found and loaded, it will be executed. If the program exits by a standard monitor method, then the supervisor will be reloaded and the READY state reached. If the program does not exit using a standard monitor method, and has not corrupted the communications area, then setting the SR to 86 decimal (126 octal) and pressing RUN should restore the READY state. Otherwise, it will be necessary to boot from the disk pack again.

TODO: Managing the "*DRS1RES" program library.