Datasheet

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11011B–ATARM–21-Feb-12
SAM3N
10.5.8 Programming hints for the synchronization primitives
ANSI C cannot directly generate the exclusive access instructions. Some C compilers provide
intrinsic functions for generation of these instructions:
The actual exclusive access instruction generated depends on the data type of the pointer
passed to the intrinsic function. For example, the following C code generates the require
LDREXB operation:
__ldrex((volatile char *) 0xFF);
10.6 Exception model
This section describes the exception model.
10.6.1 Exception states
Each exception is in one of the following states:
10.6.1.1 Inactive
The exception is not active and not pending.
10.6.1.2 Pending
The exception is waiting to be serviced by the processor.
An interrupt request from a peripheral or from software can change the state of the correspond-
ing interrupt to pending.
10.6.1.3 Active
An exception that is being serviced by the processor but has not completed.
An exception handler can interrupt the execution of another exception handler. In this case both
exceptions are in the active state.
10.6.1.4 Active and pending
The exception is being serviced by the processor and there is a pending exception from the
same source.
10.6.2 Exception types
The exception types are:
10.6.2.1 Reset
Reset is invoked on power up or a warm reset. The exception model treats reset as a special
form of exception. When reset is asserted, the operation of the processor stops, potentially at
any point in an instruction. When reset is deasserted, execution restarts from the address pro-
Table 10-8. C compiler intrinsic functions for exclusive access instructions
Instruction Intrinsic function
LDREX , LDREXH , or
LDREXB
unsigned int __ldrex(volatile void *ptr)
STREX , STREXH , or
STREXB
int __strex(unsigned int val, volatile void *ptr)
CLREX void __clrex(void)