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SWRU543–January 2019
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Cortex
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-M4 Peripherals
3.3.1.20 SYSHNDCTRL Register (Offset = D24h) [reset = 0h]
SYSHNDCTRL is shown in Figure 3-20 and described in Table 3-23.
Return to Summary Table.
The SYSHNDCTRL register enables the system handlers and indicates the pending status of the usage
fault, bus fault, memory management fault, and SVC exceptions, as well as the active status of the system
handlers. If a system handler is disabled and the corresponding fault occurs, the processor treats the fault
as a hard fault. This register can be modified to change the pending or active status of system exceptions.
An OS kernel can write to the active bits to perform a context switch that changes the current exception
type.
NOTE: This register can only be accessed from privileged mode.
CAUTION
Software that changes the value of an active bit in this register without correct
adjustment to the stacked content can cause the processor to generate a fault
exception. Ensure software that writes to this register retains and subsequently
restores the current active status. If the value of a bit in this register must be
modified after enabling the system handlers, a read-modify-write procedure
must be used to ensure that only the required bit is modified.
Figure 3-20. SYSHNDCTRL Register
31 30 29 28 27 26 25 24
RESERVED
R-0h
23 22 21 20 19 18 17 16
RESERVED USAGE BUS MEM
R-0h R/W-0h R/W-0h R/W-0h
15 14 13 12 11 10 9 8
SVC BUSP MEMP USAGEP TICK PNDSV RESERVED MON
R/W-0h R/W-0h R/W-0h R/W-0h R/W-0h R/W-0h R-0h R/W-0h
7 6 5 4 3 2 1 0
SVCA RESERVED USGA RESERVED BUSA MEMA
R/W-0h R-0h R/W-0h R-0h R/W-0h R/W-0h
LEGEND: R/W = Read/Write; R = Read only; W1toCl = Write 1 to clear bit; -n = value after reset
Table 3-23. SYSHNDCTRL Register Field Descriptions
Bit Field Type Reset Description
31-19 RESERVED R 0h
18 USAGE R/W 0h
Usage Fault Enable
0h = Disables the usage fault exception.
1h = Enables the usage fault exception.
17 BUS R/W 0h
Bus Fault Enable
0h = Disables the bus fault exception.
1h = Enables the bus fault exception.
16 MEM R/W 0h
Memory Management Fault Enable
0h = Disables the memory management fault exception.
1h = Enables the memory management fault exception.
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