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#include <pic16f84a.h>
typedef unsigned char uint8_t;
__sfr __at(0x70) UART_TX;
__sfr __at(0x71) UART_RX;
__sfr __at(0x72) UART_STATUS;
#define GRID_W 20
#define GRID_H 10
#define MAX_LEN 10
#define OVF_PER_FRAME 10
#define DIR_UP 0
#define DIR_DOWN 1
#define DIR_LEFT 2
#define DIR_RIGHT 3
static __near uint8_t snake_x[MAX_LEN];
static __near uint8_t snake_y[MAX_LEN];
static __near uint8_t snake_len;
static __near uint8_t direction;
static __near uint8_t food_x;
static __near uint8_t food_y;
static __near uint8_t score;
static volatile __near uint8_t ovf_count;
static __near uint8_t input_state; /* 0=idle, 1=got ESC, 2=got ESC+[ */
void isr(void) __interrupt(0) {
if (INTCON & 0x04) {
ovf_count++;
INTCON &= ~(uint8_t)0x04;
}
}
static void uart_send(uint8_t b) {
while (UART_STATUS & 0x01);
UART_TX = b;
}
static void uart_puts(const char *s) {
while (*s) uart_send((uint8_t)*s++);
}
static uint8_t uart_recv(void) {
if (UART_STATUS & 0x02)
return 0;
return UART_RX;
}
/* Non-blocking state machine — drains the whole FIFO each frame.
* Handles both ESC [ x (CSI) and ESC O x (SS3) cursor key modes.
* Never blocks, so a stray ESC can't freeze the game. */
static void handle_input(void) {
uint8_t c;
while (1) {
c = uart_recv();
if (c == 0) return;
switch (input_state) {
case 0:
input_state = (c == 0x1B) ? 1 : 0;
break;
case 1:
input_state = (c == '[' || c == 'O') ? 2 : 0;
break;
case 2:
switch (c) {
case 'A': if (direction != DIR_DOWN) direction = DIR_UP; break;
case 'B': if (direction != DIR_UP) direction = DIR_DOWN; break;
case 'C': if (direction != DIR_LEFT) direction = DIR_RIGHT; break;
case 'D': if (direction != DIR_RIGHT) direction = DIR_LEFT; break;
}
input_state = 0;
break;
}
}
}
static void place_food(void) {
uint8_t x = ovf_count;
uint8_t y = ovf_count;
x += x; x += x; x += x; x -= ovf_count; x += 3; /* x = ovf*7 + 3 */
y += y; y += y; y += ovf_count; y += 1; /* y = ovf*5 + 1 */
while (x >= GRID_W) x -= GRID_W;
while (y >= GRID_H) y -= GRID_H;
food_x = x;
food_y = y;
}
static void print_uint8(uint8_t v) {
uint8_t started = 0;
if (v >= 200) { uart_send('2'); v -= 200; started = 1; }
else if (v >= 100) { uart_send('1'); v -= 100; started = 1; }
{
uint8_t t = '0';
while (v >= 10) { v -= 10; t++; }
if (started || t != '0') uart_send(t);
}
uart_send(v + '0');
}
static void render(void) {
uint8_t x, y, i;
uart_puts("\x1B[H");
/* top border */
uart_send('+');
for (x = 0; x < GRID_W; x++) uart_send('-');
uart_puts("+\r\n");
for (y = 0; y < GRID_H; y++) {
uart_send('|');
for (x = 0; x < GRID_W; x++) {
uint8_t ch = ' ';
if (x == food_x && y == food_y) {
ch = '*';
} else {
for (i = 0; i < snake_len; i++) {
if (snake_x[i] == x && snake_y[i] == y) {
ch = (i == 0) ? 'O' : 'o';
break;
}
}
}
uart_send(ch);
}
uart_puts("|\r\n");
}
/* bottom border */
uart_send('+');
for (x = 0; x < GRID_W; x++) uart_send('-');
uart_puts("+\r\n");
uart_puts("Score: ");
print_uint8(score);
uart_puts(" \r\n");
}
/* returns 1 if alive, 0 if dead */
static uint8_t update(void) {
uint8_t nx, ny, i;
nx = snake_x[0];
ny = snake_y[0];
switch (direction) {
case DIR_UP: if (ny == 0) return 0; ny--; break;
case DIR_DOWN: if (ny == GRID_H-1) return 0; ny++; break;
case DIR_LEFT: if (nx == 0) return 0; nx--; break;
case DIR_RIGHT: if (nx == GRID_W-1) return 0; nx++; break;
}
/* self-collision (exclude tail: it moves away this step) */
for (i = 0; i < snake_len - 1; i++) {
if (snake_x[i] == nx && snake_y[i] == ny) return 0;
}
if (nx == food_x && ny == food_y) {
if (snake_len < MAX_LEN) snake_len++;
score++;
place_food();
}
/* shift body back, add new head */
for (i = snake_len - 1; i > 0; i--) {
snake_x[i] = snake_x[i-1];
snake_y[i] = snake_y[i-1];
}
snake_x[0] = nx;
snake_y[0] = ny;
return 1;
}
void main(void) {
uint8_t alive;
OPTION_REG = 0x07;
TMR0 = 0;
INTCON = 0xa0;
while (1) {
/* init */
direction = DIR_RIGHT;
snake_len = 3;
score = 0;
snake_x[0] = 5; snake_y[0] = 5;
snake_x[1] = 4; snake_y[1] = 5;
snake_x[2] = 3; snake_y[2] = 5;
place_food();
uart_puts("\x1B[2J\x1B[H");
alive = 1;
while (alive) {
ovf_count = 0;
while (ovf_count < OVF_PER_FRAME);
handle_input();
alive = update();
render();
PORTA ^= 0x01;
}
uart_puts("\x1B[2J\x1B[H");
uart_puts("GAME OVER score: ");
print_uint8(score);
uart_puts("\r\npress any key\r\n");
while (uart_recv() == 0); /* wait for any byte */
input_state = 0;
}
}
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