1 files changed, 73 insertions, 0 deletions
diff --git a/fw/timer0_test.c b/fw/timer0_test.c
new file mode 100644
index 0000000..ef5e622
--- /dev/null
+++ b/fw/timer0_test.c
@@ -0,0 +1,73 @@
+#include <pic16f84a.h>
+
+typedef unsigned char uint8_t;
+
+__sfr __at(0x70) UART_TX;
+__sfr __at(0x72) UART_STATUS;
+
+/*
+ * OPTION_REG 0x07: T0CS=0 (Fosc/4), PSA=0, PS=111 (1:256)
+ * At 50 MHz: overflow every 256*256 / (50M/4) = 5.24 ms → ~191 ovf/sec
+ */
+#define STATUS_RP0   0x20
+#define T0IF         0x04   /* INTCON bit 2 */
+#define T0IE         0x20   /* INTCON bit 5 */
+#define GIE          0x80   /* INTCON bit 7 */
+#define OVF_PER_SEC  191
+
+static volatile uint8_t ovf_count = 0;
+
+void isr(void) __interrupt(0) {
+    if (INTCON & T0IF) {
+        ovf_count++;
+        INTCON &= ~T0IF;
+    }
+}
+
+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 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');
+}
+
+void main(void) {
+    uint8_t seconds = 0;
+
+    /* Configure OPTION_REG (bank 1, same 7-bit addr as TMR0) */
+    STATUS |= STATUS_RP0;
+    TMR0 = 0x07;
+    STATUS &= ~STATUS_RP0;
+
+    TMR0 = 0;
+    INTCON = T0IE | GIE;    /* enable Timer0 overflow interrupt */
+
+    uart_puts("\x1B[2J\x1B[H");
+    uart_puts("Timer0 test\r\n");
+    uart_puts("-----------\r\n");
+
+    while (1) {
+        ovf_count = 0;
+        while (ovf_count < OVF_PER_SEC);   /* ISR bumps ovf_count */
+
+        uart_puts("t = ");
+        print_uint8(seconds);
+        uart_puts(" s\r\n");
+        PORTA ^= 0x01;
+        seconds++;
+    }
+}