Add picocalc stm32 i2c keyboard code

Code/picocalc_keyboard/fifo.ino

@@ -0,0 +1,58 @@
+#include "fifo.h"
+
+static struct {
+  struct fifo_item fifo[FIFO_SIZE];
+  uint8_t count;
+  uint8_t read_idx;
+  uint8_t write_idx;
+} fifo_self;
+
+uint8_t fifo_count(void)
+{
+  return fifo_self.count;
+}
+
+void fifo_flush(void)
+{
+  fifo_self.write_idx = 0;
+  fifo_self.read_idx = 0;
+  fifo_self.count = 0;
+}
+
+bool fifo_enqueue(const struct fifo_item item)
+{
+  if (fifo_self.count >= FIFO_SIZE)
+    return false;
+
+  fifo_self.fifo[fifo_self.write_idx++] = item;
+
+  fifo_self.write_idx %= FIFO_SIZE;
+  ++fifo_self.count;
+
+  return true;
+}
+
+void fifo_enqueue_force(const struct fifo_item item)
+{
+  if (fifo_enqueue(item))
+    return;
+
+  fifo_self.fifo[fifo_self.write_idx++] = item;
+  fifo_self.write_idx %= FIFO_SIZE;
+
+  fifo_self.read_idx++;
+  fifo_self.read_idx %= FIFO_SIZE;
+}
+
+struct fifo_item fifo_dequeue(void)
+{
+  struct fifo_item item = { 0 };
+  if (fifo_self.count == 0)
+    return item;
+
+  item = fifo_self.fifo[fifo_self.read_idx++];
+  fifo_self.read_idx %= FIFO_SIZE;
+  --fifo_self.count;
+
+  return item;
+}