SAM7S256_14 Datasheet, PDF (707/775 Pages) ATMEL Corporation – ARM-based Flash MCU

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40.19.3 Real Time Timer (RTT)
40.19.3.1 RTT: Possible Event Loss when Reading RTT_SR
If an event (RTTINC or ALMS) occurs within the same slow clock cycle during which the RTT_SR is read, the cor-
responding bit might be cleared. This can lead to the loss of this event.
Problem Fix/Workaround:
The software must handle the RTT event as an interrupt and should not poll RTT_SR.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
707