25.6.8.5.1 Timestamp

As part of tamper detection, the RTC can capture the counter value (COUNT/CLOCK) into the TIMESTAMP register. Three CLK_RTC periods are required to detect the tampering condition and capture the value. The TIMESTAMP value can be read once the Tamper flag in the Interrupt Flag register (INTFLAG.TAMPER) is set. If the DMA Enable bit in the Control B register (CTRLB.DMAEN) is ‘1’, a DMA request is triggered by the timestamp. To determine which tamper source caused a capture, the Tamper ID register (TAMPID) provides the detection status of each tamper channel and the tamper input event. A DMA transfer can then read both TIMESTAMP and TAMPID in succession.

A new timestamp value cannot be captured until the Tamper flag is cleared, either by reading the timestamp or by writing a ‘1’ to INTFLAG.TAMPER. If several tamper conditions occur in a short window before the flag is cleared, only the first timestamp may be logged. However, the detection of each tamper is still recorded in TAMPID.

The Tamper Input Event (TAMPEVT) is always performing a timestamp capture. To capture on the external inputs (INn), the corresponding Input Action field in the Tamper Control register (TAMPCTRL.INnACT) must be written to ‘1’. If an input is set for wake functionality, it does not capture the timestamp; however, the Tamper flag and TAMPID is still updated.

Note: The TIMESTAMP value must be read once, and INTFLAG.TAMPER must be cleared. The next value must be read only after the INTFLAG.TAMPER is set again.