X-Git-Url: https://git.wirehaze.ovh/lifeboot.git/blobdiff_plain/9ed4c073c5c0b67258262f362dea3c6cfd666e89..54bde802e46da1968ea586e37ffdc9e22e8e5572:/lifeboot.asm?ds=sidebyside diff --git a/lifeboot.asm b/lifeboot.asm index b0575ae..6d95c7c 100644 --- a/lifeboot.asm +++ b/lifeboot.asm @@ -1,138 +1,284 @@ bits 16 org 0x7c00 -%define ORG 0x7c00 -%define VGA 0xb8000 +; ============================================================================= -%define COLS 80 -%define ROWS 25 +; settings -------------------------------------------------------------------- %define DEAD ' ' ; char to represent a dead cell %define ALIVE '#' ; char to represent an alive cell %define PRINT_COLOR 0x07 ; grey on black +%define WAIT_DELAY 0x02 ; 0.131072 seconds + +; constants ------------------------------------------------------------------- + +%define COLS 80 +%define ROWS 25 +%define VGAPGSZ (COLS * ROWS * 2) + +; memory layout --------------------------------------------------------------- + +%define ORG 0x7c00 +%define VGA 0xb8000 +%define DAT ORG + 512 + +; static variables ------------------------------------------------------------ -%define GRID ORG + 512 ; current cell grid (80 * 25 bytes) -%define NEXT_GRID GRID + COLS * ROWS ; next cell grid (80 * 25 bytes) -%define XSS NEXT_GRID + COLS * ROWS ; xs() state +%define xss DAT ; xs() state (word) +%define currvgapg DAT + 2 ; current vga page near pointer (word) + +; ============================================================================= ; entry point ----------------------------------------------------------------- ; initialize segment registers +mov ax, VGA >> 4 +mov es, ax + xor ax, ax mov ds, ax -mov es, ax mov ss, ax ; set stack pointers -mov sp, ORG mov bp, ORG +mov sp, bp -; clear screen ---------------------------------------------------------------- +; clear direction flag +cld ; disable cursor -mov ch, 0x3f -mov ah, 0x01 -int 0x10 - -; clear video memory -mov cx, COLS * ROWS -mov ax, VGA >> 4 -mov es, ax -xor di, di -mov ax, (PRINT_COLOR << 8) | DEAD - -rep stosw ; fill cx words at es:di with ax - -; setup ----------------------------------------------------------------------- - -setup: +mov ch, 0x3f ; cursor start and options +mov ah, 0x01 ; set text-mode cursor shape +int 0x10 ; video services ; initialize xss mov ah, 0x00 ; get int 0x1a ; system time -mov [XSS], dx ; cx:dx = number of clock ticks since midnight +mov [xss], dx ; cx:dx = number of clock ticks since midnight -; initialize grid -mov di, GRID -mov cx, COLS * ROWS +; initialize currvgapg +mov word [currvgapg], VGAPGSZ -.initgrid: ; do { - call xs ; ax = rand - mov dl, DEAD ; dl = DEAD (likely) +; start simulation from random state ------------------------------------------ - test ax, 0b11 +start: - jnz .initgrid_nz ; if (ax % 4 == 0) - mov dl, ALIVE ; dl = ALIVE +call init_grid -.initgrid_nz: - mov [di + cx], dl ; grid[cx] = dl +; apply game of life's rules to determine the next state ---------------------- - loop .initgrid ; } while (--cx) +next_state: -jmp halt +call flip_vga_page ; display current state +call delay ; sleep a little + +call write_next_vga_page ; write the next state to the hidden page + +jmp next_state + +; ============================================================================= ; functions ------------------------------------------------------------------- +; delay() - suspend program execution temporarily ----------------------------- + +; clobbers ah, cx, dx + +delay: + +mov cx, WAIT_DELAY ; cx:dx = interval in microseconds +mov dx, 0 + +mov ah, 0x86 +int 0x15 ; wait + +ret + +; vsync_wait() - wait for display to enter the next VBlank cycle -------------- + +; clobbers ax, dx + +vsync_wait: + +mov dx, 0x3da ; input status #1 register + +.wait_on: + in al, dx + test al, 0x08 ; vertical retrace bit + jnz .wait_on + +.wait_off: + in al, dx + test al, 0x08 + jz .wait_off + +ret + ; xs() - xorshift pseudorandom number generator ------------------------------- ; output: -; ax = updated state ([XSS]) +; [xss] = updated state -; clobbers ax, dx +; clobbers bx, dx xs: -mov ax, [XSS] -mov dx, ax +mov bx, [xss] +mov dx, bx shl dx, 1 ; dx = xss << 1 -xor ax, dx ; ax = xss ^ (xss << 1) -mov dx, ax +xor bx, dx ; bx = xss ^ (xss << 1) +mov dx, bx shr dx, 3 ; dx = xss' >> 3 -xor ax, dx ; ax = xss' ^ (xss' >> 3) -mov dx, ax +xor bx, dx ; bx = xss' ^ (xss' >> 3) +mov dx, bx shl dx, 10 ; dx = xss'' << 10 -xor ax, dx ; ax = xss'' ^ (xss'' << 10) -mov [XSS], ax +xor bx, dx ; bx = xss'' ^ (xss'' << 10) +mov [xss], bx + +ret + +; init_grid() - initialize grid cells randomly -------------------------------- + +; clobbers ax, bx, cx, dx, di + +init_grid: + +mov ah, PRINT_COLOR ; ah = color attribute +mov di, [currvgapg] ; es:di -> grid start +mov cx, COLS * ROWS ; for each cell + +.write_cell: ; do { + call xs ; [xss] = rand + mov al, DEAD ; al = DEAD (likely) + + test word [xss], 0b11 + + jnz .nz ; if ([xss] % 4 == 0) + mov al, ALIVE ; al = ALIVE + +.nz: + stosw ; [es:di] = ax ; di += 2 + + loop .write_cell ; } while (--cx) + +ret + +; flip_vga_page() - flip active display page ---------------------------------- + +; clobbers ax, dx + +flip_vga_page: + +call vsync_wait + +xor word [currvgapg], VGAPGSZ ; flip currvgapg +setnz al ; al = !(currvgapg == 0) + +mov ah, 0x05 ; select active display page +int 0x10 ; video services ret -; errors ---------------------------------------------------------------------- +; alive_neighbours() ---------------------------------------------------------- + +; input: +; es:si -> current grid +; cx -> cell index + +; output: +; ax = # alive neighbours + +; clobbers ? + +alive_neighbours: + +; todo + +ret + +; write_next_cell_state() ----------------------------------------------------- + +; input: +; es:si -> current grid +; es:di -> next grid +; cx -> cell index + +; output: +; [es:di + cx * 2] = updated cell state -hello: -mov si, str.hello +; clobbers ? -; print the error message string in si and halt -; note: we assume es = VGA_SEG and ds = 0 -printerr: -xor di, di -mov ah, PRINT_COLOR +write_next_cell_state: -; es:di = video memory -; ds:si = error message -; al = current char -; ah = color attribute +call alive_neighbours ; ax = # alive neighbours -write_char: -lodsb ; al = [ds:si], si += 1 -or al, al ; on null terminator, -jz halt ; halt -stosw ; [es:di] = ax, di += 2 -jmp write_char +mov bx, cx +shl bx, 1 + +mov dx, [es:si + bx] ; dl = cell current state + +test dl, ALIVE ; if (ALIVE) { +jne 1f + +test ax, 2 ; if (n < 2) +jl .dead ; return DEAD + +test ax, 3 ; if (n > 3) +jg .dead ; return DEAD + +jmp .alive ; return ALIVE + +1: ; } + +test ax, 3 ; if (n != 3) +jne .dead ; return DEAD + +.alive: ; return ALIVE +mov dl, ALIVE +jmp .write + +.dead: +mov dl, DEAD + +.write: +mov [es:di + bx], dx + +ret + +; write_next_vga_page() ------------------------------------------------------- + +; clobbers di, si, cx + +write_next_vga_page: + +mov si, [currvgapg] ; es:si -> current page + +mov di, VGAPGSZ +xor di, si ; es:di -> next page + +xor cx, cx ; i = 0 + +.update_loop: +call write_next_cell_state + +inc cx +test cx, COLS * ROWS +jl .update_loop ; for i in [0 .. COLS * ROWS - 1] + +ret + +; halt() - stop program execution --------------------------------------------- halt: -cli ; disable interrupts + +cli ; disable interrupts hlt jmp halt -; data ------------------------------------------------------------------------ - -str: -.hello: - db "lifeboot", 0 +; ============================================================================= times 510 - ($ - $$) db 0 ; fill remaining bytes with zeroes dw 0xaa55 ; mbr magic byte