wip

[lifeboot.git] / lifeboot.asm

diff --git a/lifeboot.asm b/lifeboot.asm
index 7a70c62d1573d2260374be1c4c66319ceee07f22..6d95c7cfee143213269e43a3da317f1abff75698 100644 (file)
--- a/lifeboot.asm
+++ b/lifeboot.asm
@@ -1,77 +1,284 @@
 bits 16
 org 0x7c00
 
 bits 16
 org 0x7c00
 

-%define ORG 0x7c00                  ; where we are loaded initially
+; =============================================================================

 
 

-%define VGA_SEG 0xb800              ; video memory starts at 0xb8000
-%define VGA_COL 80
-%define VGA_ROW 25
-%define VGA_LENW VGA_COL * VGA_ROW
+; settings --------------------------------------------------------------------

 
 

-%define FILL_CHAR ' '
-%define PRINT_COLOR 0x07            ; grey on black
+%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 xss DAT             ; xs() state (word)
+%define currvgapg DAT + 2   ; current vga page near pointer (word)
+
+; =============================================================================

 
 ; entry point -----------------------------------------------------------------
 
 ; initialize segment registers
 
 ; entry point -----------------------------------------------------------------
 
 ; initialize segment registers

+mov ax, VGA >> 4
+mov es, ax
+

 xor ax, ax
 mov ds, ax
 xor ax, ax
 mov ds, ax

-mov es, ax

 mov ss, ax
 
 ; set stack pointers
 mov ss, ax
 
 ; set stack pointers

-mov sp, ORG

 mov bp, ORG
 mov bp, ORG

+mov sp, bp

 
 

-; clear screen ----------------------------------------------------------------
+; clear direction flag
+cld

 
 ; disable cursor
 
 ; disable cursor

-mov ch, 0x3f
-mov ah, 0x01
-int 0x10
+mov ch, 0x3f                ; cursor start and options
+mov ah, 0x01                ; set text-mode cursor shape
+int 0x10                    ; video services

 
 

-; clear video memory
-mov cx, VGA_LENW
-mov ax, VGA_SEG
-mov es, ax
-xor di, di
-mov ax, (PRINT_COLOR << 8) | FILL_CHAR
+; initialize xss
+mov ah, 0x00                ; get
+int 0x1a                    ;  system time
+mov [xss], dx               ; cx:dx = number of clock ticks since midnight
+
+; initialize currvgapg
+mov word [currvgapg], VGAPGSZ
+
+; start simulation from random state ------------------------------------------
+
+start:
+
+call init_grid
+
+; apply game of life's rules to determine the next state ----------------------
+
+next_state:
+
+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:
+; [xss]     = updated state
+
+; clobbers bx, dx
+
+xs:
+
+mov bx, [xss]
+mov dx, bx
+
+shl dx, 1                   ; dx = xss << 1
+xor bx, dx                  ; bx = xss ^ (xss << 1)
+mov dx, bx
+
+shr dx, 3                   ; dx = xss' >> 3
+xor bx, dx                  ; bx = xss' ^ (xss' >> 3)
+mov dx, bx
+
+shl dx, 10                  ; dx = xss'' << 10
+xor bx, dx                  ; bx = xss'' ^ (xss'' << 10)
+mov [xss], bx
+
+ret
+
+; init_grid() - initialize grid cells randomly --------------------------------
+
+; clobbers ax, bx, cx, dx, di

 
 

-rep stosw                   ; fill cx words at es:di with ax
+init_grid:

 
 

-; errors ----------------------------------------------------------------------
+mov ah, PRINT_COLOR         ; ah = color attribute
+mov di, [currvgapg]         ; es:di -> grid start
+mov cx, COLS * ROWS         ; for each cell

 
 

-hello:
-mov si, str.hello
+.write_cell:                ; do {
+    call xs                 ;     [xss] = rand
+    mov al, DEAD            ;     al = DEAD (likely)

 
 

-; 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
+    test word [xss], 0b11

 
 

-; es:di = video memory
-; ds:si = error message
-; al = current char
-; ah = color attribute
+    jnz  .nz                ;     if ([xss] % 4 == 0)
+    mov al, ALIVE           ;         al = ALIVE

 
 

-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
+.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
+
+; 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
+
+; clobbers ?
+
+write_next_cell_state:
+
+call alive_neighbours       ; ax = # alive neighbours
+
+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:
 
 halt:

-cli                     ; disable interrupts
+
+cli                         ; disable interrupts

 hlt
 jmp halt
 
 hlt
 jmp halt
 

-; data ------------------------------------------------------------------------
-
-str:
-.hello:
-    db "lifeboot", 0
+; =============================================================================

 
 times 510 - ($ - $$) db 0   ; fill remaining bytes with zeroes
 dw 0xaa55                   ; mbr magic byte
 
 times 510 - ($ - $$) db 0   ; fill remaining bytes with zeroes
 dw 0xaa55                   ; mbr magic byte