diff options
| -rw-r--r-- | .gitignore | 2 | ||||
| -rw-r--r-- | Makefile | 4 | ||||
| -rw-r--r-- | life.asm | 119 |
3 files changed, 125 insertions, 0 deletions
diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..5baabe9 --- /dev/null +++ b/.gitignore @@ -0,0 +1,2 @@ +*.o +*.prg diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..28e66d4 --- /dev/null +++ b/Makefile @@ -0,0 +1,4 @@ +run: life.prg + x64 life.prg +life.prg: life.asm + cl65 -C /usr/share/cc65/cfg/c64-asm.cfg -u __EXEHDR__ $^ -o $@ diff --git a/life.asm b/life.asm new file mode 100644 index 0000000..d04fe7f --- /dev/null +++ b/life.asm @@ -0,0 +1,119 @@ +.export init + +numL := $02 ; low byte of a 16-bit number +numH := $03 ; low byte of a 16-bit number +key_buf_len := $c6 +key_buf := $0277 + +; initialisation: clear screen and set num to point to screen mem start +init: + jsr clear_screen + ldy #$00 + lda #$04 + sta numH + lda #$00 + sta numL + jmp loop + +; main loop +loop: + ; clear keyboard buffer; otherwise program will always think a key is pressed + lda #$00 + sta key_buf_len + + jsr key_wait + lda key_buf + jsr print_byte + + ;pha + ;lda #1 + ;jsr a16b + ;pla + + inc numL + beq inc_H + jmp dinc_H + inc_H: + inc numH +dinc_H: + cmp #$30 + bne loop + jmp end + +; loops until keyboard buffer has any number of characters in it +key_wait: + ; init: pha to retrieve before rts, to keep A intact + pha +key_wait_loop: + lda key_buf_len ; shows how many keys are in key buffer + cmp #$00 + beq key_wait_loop + pla + rts + +; clear the screen by filling it with spaces +; destroys: A, Y, numL & numH (in memory) +clear_screen: + ; init: y = 0 because you can't use indirect addressing without a register, + ; load start of screen memory into numL/numH + ldy #0 + lda #$04 + sta numH + lda #$00 + sta numL + jmp cs_loop + + ; add 1 to high bit, return if $08 (screen mem only goes to $07ff) + add_carry: + inc numH + lda numH + cmp #$08 + bne cs_loop + rts + + ; store a space in current screen mem address as specified by num, branch if + ; number overflows to 0 (i.e. add 1 to high bit of 16 bit number) + cs_loop: + lda #$20 + sta (numL),y + inc numL + beq add_carry + jmp cs_loop + +; print byte in A at location in num +print_byte: + ; init: store original A in X and push Y to stack + tax + tya + pha + txa + + ldy #$00 + sbc #$40 ; convert (very vaguely) to c64 screen codes + sta (numL),y + + ; deinit: pull Y from stack and transfer original A from X to A + pla + tay + txa + rts + +; adds A to num (16 bit) (NOT WORKING) +; destroys: X +a16b: + pha + tsx + lda numL + adc $0100,x + sta numL + bcs a16b_carry + jmp a16b_end + a16b_carry: + inc numH + a16b_end: + clc + pla + rts + +end: + brk |