问题
I've been thinking for day about the following question:
In a common pc when you allocate some memory, you ask for it to the OS that keeps track of which memory segments are occupied and which ones are not, and don't let you mess around with other programs memory etc. But what about a microcontroller, I mean a microcontroller doesn't have an operating system running so when you ask for a bunch of memory what is going on? you cannot simply acess the memory chip and acess a random place cause it may be occupied... who keeps track of which parts of memory are already occupied, and gives you a free place to store something?
EDIT:
I've programmed microcontrollers in C... and I was thinking that the answer could be "language independent". But let me be more clear: supose i have this program running on a microcontroller:
int i=0;
int d=3;
what makes sure that my i and d variables are not stored at the same place in memory?
回答1:
I think the comments have already covered this...
To ask for memory means you have some operating system managing memory that you are mallocing from (using a loose sense of the term operating system). First you shouldnt be mallocing memory in a microcontroller as a general rule (I may get flamed for that statement). Can be done in cases but you are in control of your memory, you own the system with your application, asking for memory means asking yourself for it.
Unless you have reasons why you cannot statically allocate your structures or arrays or use a union if there are mutually exclusive code paths that might both want much or all of the spare memory, you can try to allocate dynamically and free but it is a harder system engineering problem to solve.
There is a difference between runtime allocation of memory and compile time. your example has nothing to do with the rest of the question
int i=0; int d=3;
the compiler at compile time allocates two locations in .data one for each of those items. the linker and/or script manages where .data lives and what its limitations are on size, if .data is bigger than what is available you should get a linker warning, if not then you need to fix your linker commands or script to match your system.
runtime allocation is managed at runtime and where and how it manages the memory is determined by that library, even if you have plenty of memory a bad or improperly written library could overlap .text, .data, .bss and/or the stack and cause a lot of problems.
excessive use of the stack is also a pretty serious system engineering problem which coming from non-embedded systems is these days often overlooked because there is so much memory. It is a very real problem when dealing with embedded code on a microcontroller. You need to know your worst case stack usage, leave room for at least that much memory if you are going to have a heap to dynamically allocate, or even if you statically allocate.
来源：https://stackoverflow.com/questions/14964985/microcontroller-memory-allocation