问题描述
我用的ARM Cortex M3的寄存器工作。在文档中，一些位都可以保留。目前还不清楚给我，我应该如何处理在寄存器写当这些预留位。
I am working with the registers of an ARM Cortex M3. In the documentation, some of the bits may be "reserved". It is unclear to me how I should deal with these reserved bits when writing on the registers.
这些是保留位，甚至可写？我应该小心不要接触他们？如果我触摸它们会坏事发生吗？
Are these reserved bits even writeable? Should I be cautious to not touch them? Will something bad happen if I touch them?
推荐答案
这是一个典型的嵌入式世界中的问题，以什么用预留位做！首先，你应该不会随机写进去，免得你的code变得无法移植。当结构分配一个新的含义在未来保留位会发生什么？您code将打破。因此，有保留与寄存器打交道时最好的口头禅位的读 - 修改 - 写。即读寄存器的内容，只修改你想要位，然后写回值，以便预留位不变（不变，并不意味着我们不写放进去，但在这个意义上，我们写道，这是有前）
This is a classic embedded world problem as to what to do with reserved bits! First, you should NOT write randomly into it lest your code becomes un-portable. What happens when the architecture assigns a new meaning to the reserved bits in future? Your code will break. So the best mantra when dealing with registers having reserved bits is Read-Modify-Write. i.e read the register contents, modify only the bits you want and then write back the value so that reserved bits are untouched ( untouched, does not mean we dont write into them, but in the sense, that we wrote that which was there before )
举例来说，说有其中仅拥有，所以LSb意义和所有其他被保留的寄存器。我会做这个
For example, say there is a register in which only the LSBit has meaning and all others are reserved. I would do this
ldr r0,=memoryAddress
ldr r1,[r0]
orr r1,r1,#1
str r1,[r0]
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