ST SPC560P34 - Figure 434. SWT Service Register (SWT_SR); Functional Description; Table 397. SWT_CO Field Descriptions; Table 398. SWT_SR Field Descriptions

Functional Safety RM0046
752/936 Doc ID 16912 Rev 5
SWT Service Key Register (SWT_SK)
The SWT Service Key (SWT_SK) register holds the previous (or initial) service key value.
This register is read only if either the SWT_CR[HLK] or SWT_CR[SLK] bits are set.
27.3.6 Functional description
The SWT is a 32-bit timer designed to enable the system to recover in situations such as
software getting trapped in a loop or if a bus transaction fails to terminate. It includes a a
control register (SWT_CR), an interrupt register (SWT_IR), time-out register (SWT_TO), a
window register (SWT_WN), a service register (SWT_SR) and a counter output register
(SWT_CO).
The SWT_CR includes bits to enable the timer, set configuration options and lock
configuration of the module. The watchdog is enabled by setting the SWT_CR.WEN bit. The
reset value of the SWT_CR.WEN bit is device specific1 (enabled). This last bit is cleared
when exiting ME RESET mode in case flash user option bit 31 (WATCHDOG_EN) is 0. If the
reset value of this bit is 1, the watchdog starts operation automatically after reset is
released. Some devices can be configured to clear this bit automatically during the boot
process.
The SWT_TO register holds the watchdog time-out period in clock cycles unless the value is
less than 0x0100, in which case the time-out period is set to 0x0100. This time-out period is
Table 397. SWT_CO field descriptions
Field Description
CNT
Watchdog Count
When the watchdog is disabled (SWT_CR.[WEN]=0) this field shows the value of the internal down
counter. When the watchdog is enabled the value of this field is 0x0000_0000. Values in this field can
lag behind the internal counter value for as many as 6 system plus 8 counter clock cycles. Therefore,
the value read from this field immediately after disabling the watchdog may be higher than the actual
value of the internal counter.
Figure 434. SWT Service Register (SWT_SR)
Address: Base + 0x0018 Access: User read/write
0123456789101112131415
R0000000000000000
W
Reset0000000000000000
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
R0000000000000000
WSK
Reset0000000000000000
Table 398. SWT_SR field descriptions
Field Description
SK
Service Key.This field is the previous (or initial) service key value used in keyed service mode. If
SWT_CR[KEY] is set, the next key value to be written to the SWT_SR is (17*SK+3) mod 2
16
.