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System
H3 Datasheet(Revision1.2) Copyright© 2015 Allwinner Technology Co.,Ltd.All Rights Reserved. Page 165
4.7. Trusted Watchdog
4.7.1. Overview
The trusted watchdog is primarily used to protect the trusted world operations from denial of service when secure
services are dependent to the RichOS scheduler. For example, if the trusted world is not entered after a defined time
limit the SoC is re-started to perform an authentication of the system.
The trusted watchdog can also be used to mask the real cause of a security error thanks to the delayed warm reset it
generates.
4.7.2. Block Diagram
24M
LOSC
TWD
Interval Value
CMP Counter
Value ==
Hi/Low Counter
Value ?
Pending
IRQ Enable IRQ
yes
Cold
Reset
Hi/Low Counter
Rolling-over
Restart
CMP Counter Value =
Hi/Low Counter Value + Interval Value
Reset
Enable
Reset
Interval Value
Register
Read Latch Enable
Clear Enable
Stop Enable
Clear
Counter?
Read Value?
Counter Value and Interval Value are
Cleared
Stop?
Hi/Low Counter
Stop Rolling-over
Resum?
Hi/Low Counter
Continue Rolling-over
Reset Flag
After
Warm
Reset
Figure 4-4. TWD Block Diagram
The trusted watchdog timer must always be running when the SoC wakes up from cold reset and can be refreshed,
suspended, or reset only by secure accesses. And a clock of at least 32 kHz is used when the device is not a power
saving cycles.
4.7.3. Functionalities Description
4.7.3.1. TWD Reset
The trusted watchdog timer is able to generate a SoC warm reset after a duration programmed into the timer or set by
default in hardware. And the flag indicating the occurrence of a watchdog triggered warm reset has occurred since the
last cold reset.
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