snake

1 files changed, 122 insertions, 0 deletions

diff --git a/fw/snake.c b/fw/snake.c
new file mode 100644
index 0000000..968379e
--- /dev/null
+++ b/fw/snake.c
@@ -0,0 +1,122 @@
+#include <pic16f84a.h>
+
+typedef unsigned char uint8_t;
+
+__sfr __at(0x70) UART_TX;
+__sfr __at(0x71) UART_RX;
+__sfr __at(0x72) UART_STATUS;
+
+/*
+ * how many OVF per refresh of the screen
+ */
+#define OVF_PER_REFRESH 80
+
+#define DIR_UP    0
+#define DIR_DOWN  1
+#define DIR_LEFT  2
+#define DIR_RIGHT 3
+
+uint8_t direction;
+uint8_t position[2];
+
+static volatile uint8_t ovf_count = 0;
+
+void isr(void) __interrupt(0) {
+    if (INTCON & 0x04) {        /* T0IF = bit 2 */
+        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;           /* rx_empty: nothing to read */
+    return UART_RX;         /* reading pops the FIFO */
+}
+
+static uint8_t uart_getc(void) {
+    while (UART_STATUS & 0x02);
+    return UART_RX;
+}
+
+static void handle_input(void) {
+    uint8_t c = uart_recv();
+    if (c != 0x1B)
+        return;
+    if (uart_getc() != '[')
+        return;
+    switch (uart_getc()) {
+        case 'A': direction = DIR_UP;    break;  /* ESC [ A */
+        case 'B': direction = DIR_DOWN;  break;  /* ESC [ B */
+        case 'C': direction = DIR_RIGHT; break;  /* ESC [ C */
+        case 'D': direction = DIR_LEFT;  break;  /* ESC [ D */
+    }
+}
+
+static void update_position(void) {
+    switch (direction) {
+        case DIR_UP:    position[1]--; break;
+        case DIR_DOWN:  position[1]++; break;
+        case DIR_LEFT:  position[0]--; break;
+        case DIR_RIGHT: position[0]++; break;
+    }
+}
+
+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) {
+    uart_puts("\x1B[H");   /* cursor home */
+
+    uart_puts("pos: ");
+    print_uint8(position[0]);
+    uart_puts(", ");
+    print_uint8(position[1]);
+    uart_puts("\r\n");
+}
+
+
+void main(void) {
+
+    OPTION_REG = 0x07;
+    TMR0 = 0;
+    INTCON = 0xa0;
+
+    direction = DIR_RIGHT;
+    position[0] = 10;
+    position[1] = 5;
+
+    uart_puts("\x1B[2J\x1B[H");
+    uart_puts("snake\r\n");
+    uart_puts("-----------\r\n");
+
+    while (1) {
+        ovf_count = 0;
+        while (ovf_count < OVF_PER_REFRESH);
+
+        handle_input();
+        update_position();
+        render();
+
+        PORTA ^= 0x01;
+    }
+}