1 files changed, 49 insertions, 0 deletions
diff --git a/01-system-clock/src/spin.c b/01-system-clock/src/spin.c
new file mode 100644
index 0000000..fbd16b6
--- /dev/null
+++ b/01-system-clock/src/spin.c
@@ -0,0 +1,49 @@
+#include "spin.h"
+#include "delay.h"
+#include "gpio.h"
+
+#define SHORT_DELAY 200000
+#define LONG_DELAY (SHORT_DELAY * 2)
+
+static void flash_bit(
+    uint32_t base, gpio_output_pin_t out_pin,
+    uint8_t bit /* 0 => 0, non-zero => 1 */)
+{
+  pin_on(out_pin);
+  if (bit) {
+    delay(base * 2);
+  } else {
+    delay(base);
+  }
+  pin_off(out_pin);
+  delay(base);
+}
+
+void spin(uint32_t base, uint8_t c)
+{
+  uint8_t code;
+  __IO gpio_port_t* port_b = enable_gpio(GPIO_PORT_B);
+  gpio_output_pin_t pin3 = set_gpio_pin_output(port_b, PIN_3);
+
+  for (;;) {
+    code = c;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+    code <<= 1;
+    flash_bit(base, pin3, code & 0x80);
+
+    delay(base * 4);
+  }
+}