问题描述
我正在为Cortex M0(ARM)CPU编写代码，并且32位读取/写入是原子的.现在我想知道何时读/写8bit/16bit变量，它们是否也保证是原子的?我的直觉说是的，因为它们在内部与32位段对齐，所以CPU不可能需要两条单独的指令来读取/写入它们.
I'm writing code for a Cortex M0 (ARM) CPU, and 32-bit reads/writes are atomic. Now I was wondering when I read/write 8bit/16bit variables, are they also guaranteed to be atomic? My instinct says yes, because they are internally aligned to 32-bit sections, so there is no possibility that the CPU needs two separate instructions to read/write them.
但是我也碰巧在打包结构中存储了很多变量以节省内存，并且变量可能没有在32位边界上对齐，因此16位值的每半都可能在不同的部分中
But I also happen to store a lot of variables in packed structures to save memory, and there it's possible that variables are not aligned on 32-bit boundaries, so each half of a 16-bit value could be in a different section.
使用压缩结构会丢失原子操作吗?
So is it true that I lose atomic operations when I use packed structures?
推荐答案
使用压缩结构，您将永远不会对与存储单元边界重叠的字段进行读/写原子操作.这意味着只能保证8位操作是原子操作，否则取决于字段的内存对齐方式.
Using packed structures you will never have read/write atomic operations on fields that overlaps a memory unit boundary. This means that only 8bits operations are guaranteed to be atomic, otherwise it depends on the memory alignment of your fields.
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