+ /*
+ * Switch to Slow oscillator clock.
+ */
+ ldr r0, [r1, #PMC_MCKR_OFF]
+ and r0, r0, #~PMC_CSS_MASK
+ str r0, [r1, #PMC_MCKR_OFF]
+wait_slowosc:
+ ldr r0, [r1, #PMC_SR_OFF]
+ tst r0, #PMC_MCKRDY
+ beq wait_slowosc
+
+ /*
+ * Switch to prescaler div 1 factor.
+ */
+ ldr r0, [r1, #PMC_MCKR_OFF]
+ and r0, r0, #~PMC_PRES_MASK
+ str r0, [r1, #PMC_MCKR_OFF]
+wait_presc:
+ ldr r0, [r1, #PMC_SR_OFF]
+ tst r0, #PMC_MCKRDY
+ beq wait_presc
+