1 files changed, 35 insertions, 0 deletions
diff --git a/fw/blink.c b/fw/blink.c
new file mode 100644
index 0000000..6789b0a
--- /dev/null
+++ b/fw/blink.c
@@ -0,0 +1,35 @@
+#include <pic16f84a.h>
+
+typedef unsigned char uint8_t;
+
+// Global volatile so sdcc cannot optimise the delay loops away.
+static volatile uint8_t _d0, _d1, _d2;
+
+// Busy-wait ~500 ms at 50 MHz.
+// 200 × 256 × 256 = 13 107 200 inner iterations.
+// Each iteration ≈ 3 uint8_t instructions × 20 ns = 60 ns.
+// Total ≈ 786 ms  (tune outer count _d0 < N to taste).
+static void delay(void) {
+    _d0 = 0;
+    do {
+        _d1 = 0;
+        do {
+            _d2 = 0;
+            do { _d2++; } while (_d2 != 0);
+        } while (++_d1 != 30);
+        _d0++;
+    } while (_d0 != 116);
+}
+
+void main(void) {
+    // port_b(0) drives activity_led at E8 on the Tang Primer 25K.
+    // port_a(0) drives led at L6.  Both ports are always outputs in this CPU.
+    while (1) {
+        PORTB = 0x01;   // activity_led (E8) on
+        PORTA = 0x01;   // led (L6) on
+        delay();
+        PORTB = 0x00;   // activity_led (E8) off
+        PORTA = 0x00;   // led (L6) off
+        delay();
+    }
+}