for it in the instruction memory, and then jump to its entry point
there.
+@c NB: In the below the mapped area's size is greater or equal to the
+@c size of all overlays. This is intentional to remind the developer
+@c that overlays don't necessarily need to be the same size.
+
@example
@group
- Data Instruction Larger
-Address Space Address Space Address Space
-+-----------+ +-----------+ +-----------+
-| | | | | |
-+-----------+ +-----------+ +-----------+<-- overlay 1
-| program | | main | | | load address
-| variables | | program | | overlay 1 |
-| and heap | | | ,---| |
-+-----------+ | | | | |
-| | +-----------+ | +-----------+
-+-----------+ | | | | |
- mapped --->+-----------+ / +-----------+<-- overlay 2
- address | overlay | <-' | overlay 2 | load address
- | area | <-----| |
- | | <---. +-----------+
- | | | | |
- +-----------+ | | |
- | | | +-----------+<-- overlay 3
- +-----------+ `--| | load address
- | overlay 3 |
- | |
- +-----------+
- | |
- +-----------+
-
- To map an overlay, copy its code from the larger address space
- to the instruction address space. Since the overlays shown here
- all use the same mapped address, only one may be mapped at a time.
+ Data Instruction Larger
+Address Space Address Space Address Space
++-----------+ +-----------+ +-----------+
+| | | | | |
++-----------+ +-----------+ +-----------+<-- overlay 1
+| program | | main | .----| overlay 1 | load address
+| variables | | program | | +-----------+
+| and heap | | | | | |
++-----------+ | | | +-----------+<-- overlay 2
+| | +-----------+ | | | load address
++-----------+ | | | .-| overlay 2 |
+ | | | | | |
+ mapped --->+-----------+ | | +-----------+
+ address | | | | | |
+ | overlay | <-' | | |
+ | area | <---' +-----------+<-- overlay 3
+ | | <---. | | load address
+ +-----------+ `--| overlay 3 |
+ | | | |
+ +-----------+ | |
+ +-----------+
+ | |
+ +-----------+
+
+ @anchor{A code overlay}A code overlay
@end group
@end example
-This diagram shows a system with separate data and instruction address
-spaces. For a system with a single address space for data and
-instructions, the diagram would be similar, except that the program
-variables and heap would share an address space with the main program
-and the overlay area.
+The diagram (@pxref{A code overlay}) shows a system with separate data
+and instruction address spaces. To map an overlay, the program copies
+its code from the larger address space to the instruction address space.
+Since the overlays shown here all use the same mapped address, only one
+may be mapped at a time. For a system with a single address space for
+data and instructions, the diagram would be similar, except that the
+program variables and heap would share an address space with the main
+program and the overlay area.
An overlay loaded into instruction memory and ready for use is called a
@dfn{mapped} overlay; its @dfn{mapped address} is its address in the
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