AN4759

RTC tamper detection function

2.9.1Timestamp firmware examples

The RTC comes with a set of example projects so that the user can quickly become familiar with this peripheral. Refer to the STM32Cube MCU Package of the product for a complete projects list.

For example, the user can find the following projects concerning timestamp:

•For the NUCLEO-L412RB-P equipped with an RTC3: STM32Cube_FW_L4_Vx.y.z\Projects\NUCLEO-L412RB-P\Examples\RTC\RTC_TimeStamp

•For the NUCLEO-G071RB equipped with an RTC3: STM32Cube_FW_G0_Vx.y.z\Projects\NUCLEO-G071RB\Examples_LL\RTC\RTC_TimeStamp_Init

If an example is not available in the STM32Cube for a given STM32 MCU, the user can adapt it.

2.10RTC tamper detection function

The RTC includes several tamper detection inputs. The tamper inputs can be configured to detect different types of tamper events. Each tamper input has an individual flag (TAMPxF in RTC_ISR (RTC2)/TAMP_SR (RTC3)).

A tamper detection event generates an interrupt when TAMPIE or TAMPxIE is set in RTC_TAMPCR (RTC2)/ TAMP_IER (RTC3).

The configuration of the tamper filter, TAMPFLT[1:0] in TAMP_FLTCR, defines whether the tamper detection is activated on edge (set TAMPFLT[1:0] = 00), or on level (TAMPFLT[1:0] ≠ 00).

The number of tamper inputs depends on product packages. Each input has a TAMPxF individual flag in RTC_ISR (RTC2)/TAMP_SR (RTC3).

The DBP bit (the register associated depends on the product), must be set to allow write access to any TAMP registers after a system reset.

2.10.1Edge detection on tamper input

When TAMPFLT[1:0] = 00, the tamper input detection triggers when a rising edge or a falling edge (depending on TAMPxTRG) is observed on the input pin RTC_TAMPx (RTC2)/TAMP_INx (RTC3).

Figure 14. Tamper with edge detection

AN4759

RTC tamper detection function

Table 15. Tamper features (edge detection)

2.10.2Level detection on tamper input

Setting TAMPFLT[1:0] to a value other than zero means that the tamper input triggers when a selected level (high or low) is observed on the corresponding input pin RTC_TAMPx (RTC2)/TAMP_INx (RTC3).

A tamper detection event is generated when either two, four or eight (depending on the TAMPFLT value) consecutive samples are observed at the selected level.

Figure 15. Tamper with level detection

Using the level detection (TAMPFLT[1:0] ≠ 0), the tamper input pin can be precharged by resetting TAMPPUDIS through an internal resistance before sampling its state. In order to support the different capacitance values, the length of the pulse during which the internal pull-up is applied can be one, two, four or eight RTCCLK cycles (see TAMPPRCH[1:0]).

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RTC tamper detection function

Figure 16. Tamper sampling with precharge pulse

Table 16. Tamper features (level detection)

2.10.3Action on tamper detection event

By setting TAMPTS = 1, any tamper event (with edge or level detection) causes a timestamp to occur. The timestamp and timestamp overflow flags are then set when the tamper flag is set and work in the same manner as when a normal timestamp event occurs.