Datasheet

201
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
12.9.1.1 Auxiliary Control Register
Name: SCB_ACTLR
Access: Read/Write
Reset: 0x000000000
The SCB_ACTLR provides disable bits for the following processor functions:
• IT folding
• Write buffer use for accesses to the default memory map
• Interruption of multi-cycle instructions.
By default, this register is set to provide optimum performance from the Cortex-M4 processor, and does not normally require
modification.
• DISOOFP: Disable Out Of Order Floating Point
Disables floating point instructions that complete out of order with respect to integer instructions.
• DISFPCA: Disable FPCA
Disables an automatic update of CONTROL.FPCA.
• DISFOLD: Disable Folding
When set to 1, disables the IT folding.
Note: In some situations, the processor can start executing the first instruction in an IT block while it is still executing the IT
instruction. This behavior is called IT folding, and it improves the performance. However, IT folding can cause jitter in
looping. If a task must avoid jitter, set the DISFOLD bit to 1 before executing the task, to disable the IT folding.
• DISDEFWBUF: Disable Default Write Buffer
When set to 1, it disables the write buffer use during default memory map accesses. This causes BusFault to be precise but
decreases the performance, as any store to memory must complete before the processor can execute the next instruction.
This bit only affects write buffers implemented in the Cortex-M4 processor.
• DISMCYCINT: Disable Multiple Cycle Interruption
When set to 1, it disables the interruption of load multiple and store multiple instructions. This increases the interrupt latency of the
processor, as any LDM or STM must complete before the processor can stack the current state and enter the interrupt handler.
12.9.1.2 CPUID Base Register
Name: SCB_CPUID
Access: Read/Write
31 30 29 28 27 26 25 24
–
23 22 21 20 19 18 17 16
–
15 14 13 12 11 10 9 8
– DISOOFP DISFPCA
76543210
–
DISFOLD DISDEFWBUF DISMCYCINT