+#if AVR_CLOCK == 8000000UL
+#define AO_CLKPS 0 /* divide by 1 */
+#define AO_CS 10 /* prescale by 512 */
+#endif
+#if AVR_CLOCK == 4000000UL
+#define AO_CLKPS 1 /* divide by 2 */
+#define AO_CS 9 /* prescale by 256 */
+#endif
+#if AVR_CLOCK == 2000000UL
+#define AO_CLKPS 2 /* divide by 4 */
+#define AO_CS 8 /* prescale by 128 */
+#endif
+#if AVR_CLOCK == 1000000UL
+#define AO_CLKPS 3 /* divide by 8 */
+#define AO_CS 7 /* prescale by 64 */
+#endif
+#if AVR_CLOCK == 500000UL
+#define AO_CLKPS 4 /* divide by 16 */
+#define AO_CS 6 /* prescale by 32 */
+#endif
+#if AVR_CLOCK == 250000UL
+#define AO_CLKPS 5 /* divide by 32 */
+#define AO_CS 5 /* prescale by 16 */
+#endif
+#if AVR_CLOCK == 125000UL
+#define AO_CLKPS 6 /* divide by 64 */
+#define AO_CS 4 /* prescale by 32 */
+#endif
+#if AVR_CLOCK == 62500UL
+#define AO_CLKPS 7 /* divide by 128 */
+#define AO_CS 4 /* prescale by 32 */
+#endif
+