IP2022 User’s Manual—Peripherals www.ubicom.com 247 value   in   the   RTTMR   register   unless   the   RTCLK   clock   is
synchronous to the system clock. If the value in the RTTMR register does not need to be used by the
CPU (i.e. only the interrupt flag is of interest) then the RTEOS bit
can be clear (i.e. RTCLK not oversampled) which allows the Real-
Time Timer to function for any configuration of the system clock. If the value in the RTTMR register needs to be used by the CPU,
but  the  Real-Time  Timer  is  not  required  to  function  when  the
system clock is set to RTCLK or turned off, then the RTEOS bit
should be set to ensure the CPU can reliably read the RTTMR
register. If the value in the RTTMR register needs to be used by the CPU
and the Real-Time Timer is required to function when the system
clock  is  set  to  RTCLK  or  off,  then  software  must  change  the
RTEOS bit when changing the system clock source. To read the
RTTMR register when the system clock is not synchronous to the
RTCLK, the RTEOS bit must be clear to ensure reliable operation.
Before the system clock is changed to RTCLK or turned off, the
RTEOS bit must be set (i.e. RTCLK not oversampled) for the Real-
Time Timer to continue to function. The  Real-Time  Timer  should  be  enabled  before  its  interrupt  is
enabled.