7.3.6.2
Functional Description
The Tamper module provides mechanisms to detect, respond, and log system tamper events. A
tamper event is detected by state transitions on up to four GPIOs. The module may respond to a
tamper event by clearing all or part of the hibernate module memory, generating a tamper event
signal to the System Control module. The event will also be logged with a RTC time stamp to allow
for tamper investigation.
Tamper Detection
Qualified tamper events are detected through an
XOSCn
pin failure or through tamper I/O level
matches which pass through a glitch filter. Tamper I/O pad events are detected by comparing the
level on a tamper I/O pad with an expected value. The tamper I/O is sampled using the hibernate
clock source and when the glitch filtering is enabled, must be stable for about 100 ms. This provides
debounce filtering of a breakaway switch as a results of a drop impact. The tamper module contains
one long glitch filter and one short glitch filter which uses an OR of the inputs as shown in Figure
7-8 on page 543. This implies if two Tamper inputs are asserted and one deasserts, the glitch filter
runs to timeout or until the second Tamper input is deasserted. The glitch filter or tamper logging
logic does not re-trigger if the tamper event match continues. The glitch filter resets on the deassertion
of the tamper conditions or when a qualified tamper event is logged.
If the
XOSCn
pins are enabled for use with the Hibernation module and subsequently fail, a tamper
event is detected and is indicated by the
STATE
field in the
HIB Tamper Status (HIBTPSTAT)
register. In addition, the
XOSCST
and
XOSCFAIL
bits can be read for further details on the external
oscillator source state.
Figure 7-8. Tamper Pad with Glitch Filtering
LONG
FILTER
SHORT
FILTER
XOSC Fail Detect Logic
TMPR0
TMPR1
XOSC0
TMPR2
TMPR3
TAMPER
EVENT
Tamper
Input Detect
Tamper
Input Detect
Tamper
Input Detect
Tamper
Input Detect
Tamper Event Responses
There are many responses to a tamper event including clearing some or all of Hibernate memory
and generating a tamper signal to the System Control Module. The descriptions of the possible
event responses follows.
543
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller