Linker scripts之MEMORY

1　　MEMORY command

　　The MEMORY command describes the location and size of blocks of memory in the target. You can use it to describe which memory regions may be used by the linker, and which memory regions it must avoid. 

　　A linker script may contain at most one use of the MEMORY command. However, you can define as many blocks of memory within it as you wish. The syntax is:

     MEMORY
       {
         name [(attr)] : ORIGIN = origin, LENGTH = len
         ...
       }

　　The name is used to refer to the region. We can add later alias names to existing memory regions with REGION_ALIAS command.

　　The attr string must consist only of the following characters:

　　　　'R', Read-only section;　　'W', Read/write section;　　'X', Executable section 

　　The origin is for the start address of the memory region. The keyword ORIGIN may be abbreviated to org or o (but not, for example, ORG).

　　The len is an expression for the size in bytes of the memory region. As with the origin expression, the expression must be numerical only and must evaluate to a constant. The keyword LENGTH may be abbreviated to len or l.

2　　Example

     MEMORY
       {
         rom (rx)  : ORIGIN = 0, LENGTH = 256K
         ram (!rx) : org = 0x40000000, l = 4M
       }

　　There are two memory regions available for allocation: one starting at `0' for 256 kilobytes, and the other starting at `0x40000000' for four megabytes. The linker will place into the `rom' memory region every section which is not explicitly mapped into a memory region, and is either read-only or executable. The linker will place other sections which are not explicitly mapped into a memory region into the `ram' memory region.