Software ordering of memory accesses tws true wireless stereo speaker

The order of instructions in the program flow does not always guarantee the order of the corresponding memory transactions. This is because:
● The processor can reorder some memory accesses to improve efficiency, providing this does not affect the behavior of the instruction sequence.
● The processor has multiple bus interfaces
● Memory or devices in the memory map have different wait states
● Some memory accesses are buffered or speculative. www.bjbjaudio.com

 Memory system ordering of memory accesses
The memory system guarantees the order of memory accesses. Otherwise, if the order of memory accesses is critical, software must include memory barrier instructions to force that ordering. The processor provides the following memory barrier instructions:
1. DMB The Data Memory Barrier (DMB) instruction ensures that outstanding memory transactions complete before subsequent memory transactions.
2.DSB The Data Synchronization Barrier (DSB) instruction ensures that outstanding memory transactions complete before subsequent
instructions execute.      <a style="opacity:0.0;color:#ffffff">tws true wireless stereo speaker</a>
3.ISB The Instruction Synchronization Barrier (ISB) ensures that the effect of all completed memory transactions is recognizable by subsequent instructions. www.bjbjaudio.com

Use memory barrier instructions in, for example:
● Vector table. If the program changes an entry in the vector table, and then enables the corresponding exception, use a DMB instruction between the operations. This ensures that if the exception is taken immediately after being enabled the processor uses the new exception vector.
● Self-modifying code. If a program contains self-modifying code, use an ISB instruction immediately after the code modification in the program. This ensures subsequent instruction execution uses the updated program.
● Memory map switching. If the system contains a memory map switching mechanism, use a DSB instruction after switching the memory map in the program. This ensures subsequent instruction execution uses the updated memory map.
● Dynamic exception priority change. When an exception priority has to change when the exception is pending or active, use DSB instructions after the change. This ensures the change takes effect on completion of the DSB instruction.
● Using a semaphore in multi-master system. If the system contains more than one bus master, for example, if another processor is present in the system, each processor must use a DMB instruction after any semaphore instructions, to ensure other bus masters see the memory transactions in the order in which they were executed.
Memory accesses to Strongly-ordered memory, such as the system control block, do not require the use of DMB instructions.www.bjbjaudio.com