Ring buffer fixes and spark time compute

STM32/CM7/Core/Inc/global_state.h

@@ -6,6 +6,7 @@
 #include <stdint.h>
 
 #define MAX_CAM_MISS 2
+#define SPARK_ADVANCE 20
 
 typedef enum { SYNC_OK = 0, SYNC_PENDING = 1, SYNC_NOT_OK = 2 } sync_state_t;