NXP Semiconductors LPC1751, Руководство пользователя, Страница: 746 / 808

DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0 © NXP B.V. 2009. All rights reserved.
User manual Rev. 00.06 — 5 June 2009 746 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
[1] Enable bits, set to 1 to enable the exception, or set to 0 to disable the exception.
[2] Pending bits, read as 1 if the exception is pending, or as 0 if it is not pending. You can write to these bits to
change the pending status of the exceptions.
[3] Active bits, read as 1 if the exception is active, or as 0 if it is not active. You can write to these bits to change
the active status of the exceptions, but see the Caution in this section.
If you disable a system handler and the corresponding fault occurs, the processor treats
the fault as a hard fault.
You can write to this register 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.
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.
•
After you have enabled the system handlers, if you have to change the value of a bit
in this register you must use a read-modify-write procedure to ensure that you change
only the required bit.
Table 639. SHCSR bit assignments
Bits Name Function
[31:19] - Reserved
[18] USGFAULTENA Usage fault enable bit, set to 1 to enable
[1]
[17] BUSFAULTENA Bus fault enable bit, set to 1 to enable
[1]
[16] MEMFAULTENA Memory management fault enable bit, set to 1 to enable
[1]
[15] SVCALLPENDED SVC call pending bit, reads as 1 if exception is pending
[2]
[14] BUSFAULTPENDED Bus fault exception pending bit, reads as 1 if exception is
pending
[2]
[13] MEMFAULTPENDED Memory management fault exception pending bit, reads as 1 if
exception is pending
[2]
[12] USGFAULTPENDED Usage fault exception pending bit, reads as 1 if exception is
pending
[2]
[11] SYSTICKACT SysTick exception active bit, reads as 1 if exception is active
[3]
[10] PENDSVACT PendSV exception active bit, reads as 1 if exception is active
[9] - Reserved
[8] MONITORACT Debug monitor active bit, reads as 1 if Debug monitor is active
[7] SVCALLACT SVC call active bit, reads as 1 if SVC call is active
[6:4] - Reserved
[3] USGFAULTACT Usage fault exception active bit, reads as 1 if exception is
active
[2] - Reserved
[1] BUSFAULTACT Bus fault exception active bit, reads as 1 if exception is active
[0] MEMFAULTACT Memory management fault exception active bit, reads as 1 if
exception is active