# Game of Life in CUSP Assembly Homework Sample

The game of life was designed by John Conway, and is an example of a cellular automata. It consists of 3 basic rules, if a cell has less than 2 neighbors it dies of loneliness, and if it has more than 3 it dies of overcrowding, and if a cell has 3 neighbors it becomes alive. Although it sounds very simple, it can lead to very complex behavior. 3 cells in a straight line is called a blinker, and alternates between horizontal and vertical. You can assume cells outside the grid are always 0 (dead). For more assembly language programming assignments contact us for a quote.

Solution:

hw6.csp

.EQU KEYB_VECTOR,\$FF8 ; keyboard interrupt vector
.EQU @,\$000 ; main program start address
main:
LDS# \$E00 ; initialize stack to \$E00

LDA# keyboardISR
STA KEYB_VECTOR ; save isr routine address in vector

CLR generation ; start in generation 0

LDA# array1 ; save ptr to array 1 in variable
STA arr1ptr
LDA# array2 ; save ptr to array 2 in variable
STA arr2ptr

PSH# startlen ; length of string
PSH# startmsg ; string to print
JSR \$E05 ; prints starting message
ADS# 2 ; restore stack pointer
JSR \$E06 ; prints newline separation
JSR \$E06 ; prints newline separation

; Print grid
PSH arr1ptr ; address of array of current grid
PSH rows ; number of rows
PSH columns ; number of columns
PSH generation
JSR printGrid ; print grid
ADS# 4 ; restore stack pointer
start:
PSH# prmlen ; length of string
PSH# prompt ; string to print
JSR \$E05 ; prints prompt
ADS# 2 ; restore stack pointer

STA ngen ; save input in ngen
JSR \$E06 ; prints newline separation

CMA# 0
JEQ exit
generate:
PSH arr1ptr ; address of array of current grid
PSH rows ; number of rows
PSH columns ; number of columns
PSH arr2ptr ; address of array of new grid
JSR nextGen ; calculate next grid
ADS# 4 ; restore stack pointer

INC generation

; Print grid
PSH arr2ptr ; address of array of current grid
PSH rows ; number of rows
PSH columns ; number of columns
PSH generation
JSR printGrid ; print grid
ADS# 4 ; restore stack pointer

; swap pointers
LDA arr1ptr
LDX arr2ptr
STA arr2ptr
STX arr1ptr

CLR endwait ; clear keyboard wait flag
LDA# \$80 ; enable keyboard interrupts
OUTB \$0
SIE ; enable interrupts
LDA count ; set count for initializing timer
OUTW \$31
LDA# \$50 ; disable timer interrupt, clear ready bit, load and start timer
OUTB \$030
waitTimer:
INB \$030 ; read status register
AND# \$80 ; see if count is complete
JNE countdone ; if so, exit loop
LDA endwait ; see if keyboard was pressed
CMA# 1
JNE waitTimer ; if not, keep waiting
countdone:
CIE ; disable interrupts

DEC ngen ; decrement number of generations to print
JNE generate ; repeat if not zero

JMP start ; start over
exit:
PSH# endlen ; length of string
PSH# endmsg ; string to print
JSR \$E05 ; prints end of program
ADS# 2 ; restore stack pointer

HLT ; terminate program

; printGrid subroutine
.EQU grid,5
.EQU nr,4
.EQU nc,3
.EQU gen,2
printGrid:
PSHF ; push FP on stack
TSF ; load stack pointer in FP

PSH# genlen ; length of string
PSH# genmsg ; string to print
JSR \$E05 ; prints generation
ADS# 2 ; restore stack pointer
LDA ! gen
JSR \$E00 ; prints the generation number

LDX# 0 ; start at position 0 in array
CLR Y ; initialize row index to zero
forY:
CLR X ; initialize column index to zero
forX:
LDA& ! grid ; load value from array

CMA# 0 ; see if the cell was dead
JEQ cell0
cell1:
LDA# ‘*’ ; char to print
JSR \$E08 ; prints a star
cell0:
LDA# ‘.’ ; char to print
JSR \$E08 ; prints a dot
LDA# ‘ ‘ ; char to print
JSR \$E08 ; prints a space

ADX# 1 ; increment array position

INC X ; increment column index
LDA X ; load index in ACC
CMA ! nc ; compare with number of columns
JLT forX ; if I < nColumns, continue loop

JSR \$E06 ; print carriage return

INC Y ; increment row index
LDA Y ; load index in ACC
CMA ! nr ; compare with number of rows
JLT forY ; if I < nRows, continue loop

JSR \$E06 ; print carriage return

POPF ; restore FP from stack

; Keyboard Interrupt Service Routine
keyboardISR:
PSHA ; save A in stack
INC endwait ; set endwait to 1 to terminate wait
LDA# \$40 ; disable keyboard interrupt and flush buffer
OUTB \$0
POPA ; recover A
IRTN

; Variables used in main
Y: .word 0 ; row index
X: .word 0 ; column index
PTR: .word 0
generation: .word 0
ngen: .word 0
count: .word 1000000
startmsg: .char ‘Here is the starting grid:’,startlen
genmsg: .char ‘Generation: ‘,genlen
prompt: .char ‘How many new generations would you like to print (enter 0 to end)?’,prmlen
endmsg: .char ‘End of program.’,endlen
endwait: .word 0
arr1ptr: .word 0
arr2ptr: .word 0
array1: .word 0
.word 0
.word 0
.word 0
.word 0
.word 0
.word 0

.word 0
.word 0
.word 1
.word 0
.word 0
.word 0
.word 0

.word 0
.word 0
.word 0
.word 1
.word 0
.word 0
.word 0

.word 0
.word 1
.word 1
.word 1
.word 0
.word 0
.word 0

.word 0
.word 0
.word 0
.word 0
.word 0
.word 0
.word 0

.word 0
.word 0
.word 0
.word 0
.word 0
.word 0
.word 0

array2: .blkw 42,0
rows: .word 6
columns: .word 7

; NextGen subroutine
.EQU @,\$400 ; subroutine start address
.EQU curGrid,5
.EQU nRows,4
.EQU nColumns,3
.EQU nextGrid,2
nextGen:
PSHF ; push FP on stack
TSF ; load stack pointer in FP

CLR I ; initialize row index to zero
forRow:
CLR J ; initialize column index to zero
forCol:
LDA I ; load current row
MUL ! nColumns ; multiply row by ncolumns
STA pos ; save position in pos

LDA I
CMA# 0 ; see if row == 0
JEQ midleft ; if so, test middle neighbors
uptop:
LDA J
CMA# 0 ; see if col == 0
JEQ upmiddle ; if so, test up middle neighbor

LDX pos ; get position
SBX ! nColumns ; subtract ncolumns to get position in previous row
SBX# 1 ; subtract 1 to get position at top left
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
upmiddle:
LDX pos ; get position
SBX ! nColumns ; subtract ncolumns to get position in previous row
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
upright:
LDA J
CMA ! nColumns ; see if col >= n columns
JGE midleft ; if so, test midleft neighbor

LDX pos ; get position
SBX ! nColumns ; subtract ncolumns to get position in previous row
ADX# 1 ; get position at top right
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
midleft:
LDA J
CMA# 0 ; see if col == 0
JEQ midright ; if so, test middle right neighbor

LDX pos ; get position
SBX# 1 ; get position at left
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
midright:
LDA J
CMA ! nColumns ; see if col >= n columns
JGE down ; if so, test down neightbors

LDX pos ; get position
ADX# 1 ; get position at right
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors

down:
LDA I
CMA ! nRows ; see if row + 1 >= n rows
JGE updatecell ; if so, update cell

dnleft:
LDA J
CMA# 0 ; see if col == 0
JEQ dnmiddle ; if so, test down middle neighbor

LDX pos ; get position
ADX ! nColumns ; add ncolumns to get position in next row
SBX# 1 ; subtract 1 to get position at down left
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
dnmiddle:
LDX pos ; get position
ADX ! nColumns ; add ncolumns to get position in next row
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors
dnright:
LDA J
CMA ! nColumns ; see if col >= n columns
JGE updatecell ; if so, update cell

LDX pos ; get position
ADX ! nColumns ; add ncolumns to get position in next row
ADX# 1 ; get position at down right
LDA& ! curGrid ; load value from array
STA neighbors ; update number of neighbors

updatecell:
LDX pos ; get position
LDA& ! curGrid ; load value from array
STA& ! nextGrid ; copy cell to next grid

CMA# 0 ; see if the cell was dead
alive:
LDA neighbors ; load number of neighbors of current cell
CMA# 1 ; see if there are 1 or less neighbors
JGT testoc ; if there are more than 1, test overcrowding
LDA# 0 ; else, clear A to kill cell
STA& ! nextGrid ; set cell as dead in next grid
JMP next ; continue the loop
testoc:
CMA# 4 ; see if there are 4 or more neighbors
JLT next ; if there are less than 4, go to next cell
LDA# 0 ; else, clear A to kill cell
STA& ! nextGrid ; set cell as dead in next grid
JMP next ; continue the loop
LDA neighbors ; load number of neighbors of current cell
CMA# 3 ; see if there are exactly 3 neighbors
JNE next ; if there are not 3 neighbors, go to next cell
LDA# 1 ; else, set A to make cell alive
STA& ! nextGrid ; set cell as alive in next grid
next:
INC J ; increment column index
LDA J ; load index in ACC
CMA ! nColumns ; compare with number of columns
JLT forCol ; if I < nColumns, continue loop

INC I ; increment row index
LDA I ; load index in ACC
CMA ! nRows ; compare with number of rows
JLT forRow ; if I < nRows, continue loop

POPF ; restore FP from stack