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2014-07-02 - Tiny Gecko Family - d0034_Rev1.20
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• Serial Wire Clock input (SWCLK): This pin is enabled after reset and has a built-in pull down.
• Serial Wire Data Input/Output (SWDIO): This pin is enabled after reset and has a built-in pull-up.
• Serial Wire Viewer (SWV): This pin is disabled after reset.
The debug pins can be enabled and disabled through GPIO_ROUTE, see Section 28.3.4.1 (p. 471)
. Please remeberer that upon disabling, debug contact with the device is lost. Also note that, because
the debug pins have pull-down and pull-up enabled by default, leaving them enabled might increase the
current consumption with up to 200 µA if left connected to supply or ground.
6.3.2 Debug and EM2/EM3
Leaving the debugger connected when issuing a WFI or WFE to enter EM2 or EM3 will make the system
enter a special EM2. This mode differs from regular EM2 and EM3 in that the high frequency clocks
are still enabled, and certain core functionality is still powered in order to maintain debug-functionality.
Because of this, the current consumption in this mode is closer to EM1 and it is therefore important to
disconnect the debugger before doing current consumption measurements.
6.4 Debug Lock and Device Erase
The debug access to the Cortex-M3 is locked by clearing the Debug Lock Word (DLW) and resetting
the device, see Section 7.3.2 (p. 32) .
When debug access is locked, the debug interface remains accessible but the connection to the Cortex-
M3 core and the whole bus-system is blocked as shown in Figure 6.2 (p. 27) . This mechanism is
controlled by the Authentication Access Port (AAP) as illustrated by Figure 6.1 (p. 26) . The AAP is
only accessible from a debugger and not from the core.
Figure 6.1. AAP - Authentication Access Port
SW- DP
AHB- AP
Cortex
SerialWire
debug
int erface
DEVICEERASE
Aut hent icat ion
Access Port
(AAP)
ERASEBUSY
DLW[3:0] = = 0x F
The debugger can access the AAP-registers, and only these registers just after reset, for the time of the
AAP-window outlined in Figure 6.2 (p. 27) . If the device is locked, access to the core and bus-system
is blocked even after code execution starts, and the debugger can only access the AAP-registers. If the
device is not locked, the AAP is no longer accessible after code execution starts, and the debugger can
access the core and bus-system normally. The AAP window can be extended by issuing the bit pattern
on SWDIO/SWCLK as shown in Figure 6.3 (p. 27) . This pattern should be applied just before reset
is deasserted, and will give the debugger more time to access the AAP.
Summary of Contents for EFM32TG
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