CARDIAC Simulation using PC/370 - Part 2
CARDIAC Simulation - Part 1 - Introduction to CARDIAC
CARDIAC Simulation - Part 2 - Primary Logic/Architecture
CARDIAC Simulation - Part 3 - Memory Design / Management
CARDIAC Simulation - Part 4 - CARDIAC Instruction Set Processing
Welcome back to the 2nd part of my CARDIAC Simulation project (See Part 1 for an Overview). In short CARDIAC represents a mini-CPU with it's own Assembly Language Instruction Set, corresponding Machine Code & active logic flow. It can perform basic functions such as reading input, adding/subtracting, branching & more. My daughter's college computer class used this to demonstrate CPU functionality. It looked pretty cool. I told her I was going to create my own version of the simulator - just for fun of course.
Once again I'm compelled to add a small disclaimer. This exercise was purely for enjoyment within a very limited time frame. It is not an Assembler "purity" test where everyone's individual concept of "purity" should be adhered to. It is strictly a PC/370 version using DOS Interrupts that emulate 370 SVC Calls. There's a multitude of ways & methods to do this... I chose this way. It's slick, elegant, very solid & developed very rapidly.
Time to Design & Build the CARDIAC Simulator
Above: Constructing the CARDIAC Simulator. Spoiler Alert - It works perfectly!
Since the program is mimicking a mini-CPU I decided to call the program TDCPU.ALC - short & sweet.
Designing the Screen Layout - 24x80
My first step was sketching out a screen design suitable for PC/370. It needs to fit nicely within the 24x80 text screen limitation while being aesthetically pleasing with a reasonable resemblance to the online GUI version of the simulator. Unlike GUI development I have to maintain every aspect of the display including calculating cell position to drop data & code into.
|....5...10...15...20...25...30...35...40...45...50...55...60...65...70...75...80|
==|================================================================================|
01|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|
02|x x|
03|x CARDIAC CPU SIMULATION <F1>=STEP <F4>=RESET <ESC>=EXIT x|
04|x x|
05|x 00 10 20 30 40 50 60 70 80 90 x|
06|x ==== ==== ==== ==== ==== ==== ==== ==== ==== ==== x|
07|x 0:____ 0:____ 0:____ 0:____ 0:____ 0:____ 0:____ 0:____ 0:____ 0:____ x|
08|x 1:____ 1:____ 1:____ 1:____ 1:____ 1:____ 1:____ 1:____ 1:____ 1:____ x|
09|x 2:____ 2:____ 2:____ 2:____ 2:____ 2:____ 2:____ 2:____ 2:____ 2:____ x|
00|x 3:____ 3:____ 3:____ 3:____ 3:____ 3:____ 3:____ 3:____ 3:____ 3:____ x|
11|x 4:____ 4:____ 4:____ 4:____ 4:____ 4:____ 4:____ 4:____ 4:____ 4:____ x|
12|x 5:____ 5:____ 5:____ 5:____ 5:____ 5:____ 5:____ 5:____ 5:____ 5:____ x|
13|x 6:____ 6:____ 6:____ 6:____ 6:____ 6:____ 6:____ 6:____ 6:____ 6:____ x|
14|x 7:____ 7:____ 7:____ 7:____ 7:____ 7:____ 7:____ 7:____ 7:____ 7:____ x|
15|x 8:____ 8:____ 8:____ 8:____ 8:____ 8:____ 8:____ 8:____ 8:____ 8:____ x|
16|x 9:____ 9:____ 9:____ 9:____ 9:____ 9:____ 9:____ 9:____ 9:____ 9:____ x|
17|x x|
18|x PC: ___ ACC: ____ IR: ___ OPCODE: ____ OPERAND: ___ x|
19|x x|
20|x READER: xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,*** x|
21|x x|
22|x OUTPUT: xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx,xxxx x|
23|x x|
24|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|
I was happy with the screen design... just enough room to maneuver without looking too crammed.
Input File - CODE & DATA DECK - TDCPU.TXT
The online CARDIAC simulator requires the user to type in the 3 digit code/values on the web page. Each time you return to the page it must be refreshed - that's a lot of tedious redundant typing. I decided to create an input file containing the full source & object code as well as the data values to be used. This way multiple CARDIAC programs can be maintained & tested.
****:PC OOO LLLLLLLL MNE OOOOOOOO XXXXXXXXXXXXXXXXXXXXXXXXXXXX
CODE:00 001 DATA 001 ;Initialize Cell 00
CODE:04 000 ctr DATA 000 ;Initialize Counter
CODE:05 000 sum DATA 000 ;Initialize Sum
CODE:06 001 one DATA 001 ;Set Static Variable 1
CODE:07 000 num DATA 000 ;Initialize Input Number
*
CODE:10 007 loop INP num ;Read/Store Input Value
CODE:11 107 CLA num ;Load Accumulator with Value
CODE:12 315 TAC print ;Exit Loop when Negative
CODE:13 861 JMP xproc ;Perform xproc Subroutine
CODE:14 810 JMP loop ;Loop for next Input Value
CODE:15 504 print OUT ctr ;Display Record Count
CODE:16 505 OUT sum ;Display Sum Total
CODE:17 900 HRS 00 ;Halt/Reset Program (DONE)
*
CODE:60 000 xsave DATA 000 ;Accumulator Save Area
CODE:61 660 xproc STO xsave ;Store Accumulator Value
CODE:62 199 CLA ret99 ;Retrieve Return Address
CODE:63 671 STO xexit ;Push Return to Exit
CODE:64 105 CLA sum ;Load Accumulator with Sum
CODE:65 207 ADD num ;Add Input Value
CODE:66 605 STO sum ;Store Accumulator to Sum
CODE:67 104 CLA ctr ;Load Accumulator with Count
CODE:68 206 ADD one ;Add 1 to Accumulator
CODE:69 604 STO ctr ;Store Accumulator to Ctr
CODE:70 160 CLA xsave ;Restore Accumulator Value
CODE:71 800 xexit JMP 00 ;Return to Main Process
*
CODE:99 800 ret99 DATA 800 ;Return Address Area (JMP)
*
****:+NN
DECK:001
DECK:002
DECK:004
DECK:008
DECK:-01
Mainline Processing Logic
The first step of the TDCPU program is to read the input data file (TDCPU.TXT) containing the source/object code and any input data values (if necessary). The Code & data is then stored in the tables CTAB & DTAB. These tables are used to initially populate the Memory Cells and when the <F4> RESET function is pressed. The Main Loop writes the current Memory State to the Screen Variables which are then displayed. The <F1> STEP key will then step through the code associated with the Program Counter - with each opcode branching to the appropriate function. Once the Halt/Reset instruction is executed the <F1> STEP key is inactivated - only <ESC> EXIT & <F4> RESET are permitted. <F4> will reset the program counter, re-initialize memory & re-activate the <F1> STEP key.
***********************************************************************
* MAINLINE PROCEDURE *
***********************************************************************
PRINT NOGEN
SVC @TRACE ISSUE SUPERVISOR CALL
DC CL4'IOF ' KEYBOARD INTERRUPT OFF
*
XFILO STDWKO OPEN OUTPUT FILE
*
BAL 6,DATA LOAD CODE/DECK DATA
RESET EQU *
BAL 6,INIT INITIALIZE MEMORY
LOOP EQU *
BAL 6,MEMSCR WRITE MEMORY TO SCREEN
BAL 6,SCREEN BUILD SCREEN
*
CLI KEY,@K#ESC KEY = ESCAPE ???
BE LOOPX YES - EXIT PLEASE
CLI KEY,@K#F4 KEY = <F4> ???
BE RESET YES - RESET CARDIAC
*
CP XPC,=P'0' HALT EXECUTED?
BE LOOP YES - ONLY RESET/EXIT
*
CLI KEY,@K#F1 KEY = <F1> ???
BNE LOOP NO - DISPLAY SCREEN
*
LA 7,MEMTAB LOAD MEMORY ADDRESS
ZAP DUBB,XPC MOVE PROGRAM COUNTER
CVB 3,DUBB CONVERT TO BINARY
MH 3,=H'8' MULTIPLY BY LENGTH
AR 7,3 ADJUST MEMORY PTR
*
MVC XIR,0(7) SET INSTRUCT REGISTER
LA 8,OPTAB LOAD OPERATION TABLE
IRLOOP EQU *
CLI 0(8),X'FF' END OF TABLE???
BE LOOP YES - INVALID OPCODE
CLC 0(1,8),XIR OPCODE MATCH???
BE IRFOUND YES - EXIT OPCODE LOOP
LA 8,8(,8) BUMP OPCODE POINTER
B IRLOOP TEST NEXT OPCODE
IRFOUND EQU *
MVC XMNE,1(8) MOVE INSTRUCTION MNEMONIC
ZAP ZPC,XPC SAVE PRIOR INSTRUCTION
AP XPC,=P'1' BUMP PROGRAM COUNTER
UNPK XPCU,XPC UNPACK PROGRAM COUNTER
OI XPCU+2,X'F0' TURN ON ZONE BITS
L 5,4(8) LOAD INSTRUCTION ADDRESS
BALR 6,5 PERFORM INSTRUCTION
B LOOP DISPLAY SCREEN AGAIN
LOOPX EQU *
B RETURN EXIT PROGRAM PLEASE
***********************************************************************
Build Screen Routine
I developed a generic Screen Display routine that utilizes a WTO Supervisor call that is mapped to Windows PC-Based DOS Interrupts. The table SCTAB contains all the variables that displayed on the page. My algorithm & supporting custom copybooks allow very quick development - even in complex scenarios. The <F1>, <F4> & <ESC> keys break out of the routine and returns to the main loop.
***********************************************************************
* BUILD SCREEN *
***********************************************************************
DC F'0' RETURN ADDRESS SAVE AREA
SCREEN EQU *
ST 6,*-4 SAVE RETURN ADDRESS
*
MVI VBITS,@BKWT SET BG(BLACK)/FG(WHITE)
BAL 6,VRESET CHANGE SCREEN ATTRIBUTES
*
* DISPLAY SINGLE BOX
*
MVC VBX,VBOX2 LOAD BOX FRAME
MVC VBXRC,BXTAB LOAD BOX COORDINATES
BAL 6,VBOX DISPLAY BOX FRAME
*
* DISPLAY SCREEN TEXT
*
LA 5,SCTAB LOAD TABLE ADDRESS
SC1LP EQU *
CLI 0(5),X'FF' END OF TABLE ???
BE SC1LPX YES - EXIT LOOP PLEASE
*
MVC VXYS,0(5) MOVE CURSOR POSITION
BAL 6,VXYSET SET CURSOR POSITION
L 2,4(5) LOAD MESSAGE ADDRESS
SVC @WTO ISSUE SUPERVISOR CALL
*
LA 5,8(,5) BUMP TABLE POINTER
B SC1LP TEST NEXT TABLE ENTRY
SC1LPX EQU *
*
* ACCEPT KEYSTROKE
*
BAL 6,KBGET READ KEYBOARD INPUT
MVC KEY,KBCHR STORE KEYSTROKE
*
CLI KEY,@K#ESC KEY = ESCAPE ???
BE SC2LPX YES - EXIT ROUTINE
CLI KEY,@K#F1 KEY = F1 ???
BE SC2LPX YES - EXIT ROUTINE
CLI KEY,@K#F4 KEY = F4 ???
BE SC2LPX YES - EXIT ROUTINE
*
B SC1LPX BACK TO KEYBOARD
SC2LPX EQU *
MVI VBITS,@BKWT SET BG(BLACK)/FG(WHITE)
BAL 6,VRESET CHANGE SCREEN ATTRIBUTES
SCREENX EQU *
L 6,SCREEN-4 RESTORE LINK REGISTER
BR 6 BRANCH ON LINK REGISTER
***********************************************************************
Screen Definition
Below are the primary definitions for the SCREEN Build Routine. Screen variable addresses & their X-Y coordinates are listed in SCTAB. The SCRMEM0 thru SCRMEM9 lines will contain the 100 CARDIAC Memory Cell values. Other display fields include CARDIAC internal registers, instructions, deck reader queue & print output.
***********************************************************************
* BOX COMPONENTS (COORDINATES/FRAME) *
***********************************************************************
BXTAB DS 0F
DC AL1(0,0,23,79) BOX COORDINATES/FRAME
***********************************************************************
* SCREEN DISPLAY COMPONENTS *
***********************************************************************
SCTAB DS 0F
DC AL1(0,0,2,3),A(SCRHDR) SCREEN COORDINATES/MSG
DC AL1(0,0,4,7),A(SCRTTL) SCREEN COORDINATES/MSG
DC AL1(0,0,5,7),A(SCRDASH) SCREEN COORDINATES/MSG
DC AL1(0,0,6,5),A(SCRMEM0) SCREEN COORDINATES/MSG
DC AL1(0,0,7,5),A(SCRMEM1) SCREEN COORDINATES/MSG
DC AL1(0,0,8,5),A(SCRMEM2) SCREEN COORDINATES/MSG
DC AL1(0,0,9,5),A(SCRMEM3) SCREEN COORDINATES/MSG
DC AL1(0,0,10,5),A(SCRMEM4) SCREEN COORDINATES/MSG
DC AL1(0,0,11,5),A(SCRMEM5) SCREEN COORDINATES/MSG
DC AL1(0,0,12,5),A(SCRMEM6) SCREEN COORDINATES/MSG
DC AL1(0,0,13,5),A(SCRMEM7) SCREEN COORDINATES/MSG
DC AL1(0,0,14,5),A(SCRMEM8) SCREEN COORDINATES/MSG
DC AL1(0,0,15,5),A(SCRMEM9) SCREEN COORDINATES/MSG
DC AL1(0,0,17,12),A(SCRVAR) SCREEN COORDINATES/MSG
DC AL1(0,0,19,3),A(SCRRDRT) SCREEN COORDINATES/MSG
DC AL1(0,0,19,11),A(SCRRDR) SCREEN COORDINATES/MSG
DC AL1(0,0,21,3),A(SCROUTT) SCREEN COORDINATES/MSG
DC AL1(0,0,21,11),A(SCROUT) SCREEN COORDINATES/MSG
DC XL1'FF' END OF TABLE
***********************************************************************
SCRHDR DC C'CARDIAC CPU SIMULATION <F1>=STEP'
DC C' <F4>=RESET <ESC>=EXIT',C'$'
SCRTTL DC C'00 10 20 30 40 '
DC C'50 60 70 80 90',C'$'
SCRDASH DC C'==== ==== ==== ==== ==== '
DC C'==== ==== ==== ==== ====',C'$'
SCRMEM0 DC C'0:____ 0:____ 0:____ 0:____ 0:____ '
DC C'0:____ 0:____ 0:____ 0:____ 0:____',C'$'
SCRMEM1 DC C'1:____ 1:____ 1:____ 1:____ 1:____ '
DC C'1:____ 1:____ 1:____ 1:____ 1:____',C'$'
SCRMEM2 DC C'2:____ 2:____ 2:____ 2:____ 2:____ '
DC C'2:____ 2:____ 2:____ 2:____ 2:____',C'$'
SCRMEM3 DC C'3:____ 3:____ 3:____ 3:____ 3:____ '
DC C'3:____ 3:____ 3:____ 3:____ 3:____',C'$'
SCRMEM4 DC C'4:____ 4:____ 4:____ 4:____ 4:____ '
DC C'4:____ 4:____ 4:____ 4:____ 4:____',C'$'
SCRMEM5 DC C'5:____ 5:____ 5:____ 5:____ 5:____ '
DC C'5:____ 5:____ 5:____ 5:____ 5:____',C'$'
SCRMEM6 DC C'6:____ 6:____ 6:____ 6:____ 6:____ '
DC C'6:____ 6:____ 6:____ 6:____ 6:____',C'$'
SCRMEM7 DC C'7:____ 7:____ 7:____ 7:____ 7:____ '
DC C'7:____ 7:____ 7:____ 7:____ 7:____',C'$'
SCRMEM8 DC C'8:____ 8:____ 8:____ 8:____ 8:____ '
DC C'8:____ 8:____ 8:____ 8:____ 8:____',C'$'
SCRMEM9 DC C'9:____ 9:____ 9:____ 9:____ 9:____ '
DC C'9:____ 9:____ 9:____ 9:____ 9:____',C'$'
SCRVAR DC C'PC: __ ACC: ____ IR: ___ '
DC C'OPCODE: ___ OPERAND: __ ',C'$'
SCRRDRT DC CL7'READER:',C'$'
SCRRDR DC CL66' ',C'$'
SCROUTT DC CL7'OUTPUT:',C'$'
SCROUT DC CL66' ',C'$'
***********************************************************************
This is primarily supporting architecture for the PC/370 CARDIAC Simulator. The trickiest part of the entire process was aligning the cell values with the proper position on the screen. Using the variables SCRMEM0 thru SCRMEM9 as a single table each ten's position has a horizontal offset multiplier of 7 while the one's position has a vertical offset of 70. For example, cell 73 would be in position 7*7 + 3*70 = 259. That would be 8th column (heading=70) residing on the 4th line (SCRMEM3).
More to come... much more...
