Microchip Technology SW006022-1N Data Sheet
Functions
2012 Microchip Technology Inc.
DS52071B-page 157
10.5
CHANGING THE DEFAULT FUNCTION ALLOCATION
Cases may arise when a specific function must be located at a specific address, or
within some range of addresses. The easiest way to accomplish this is by using the
address
within some range of addresses. The easiest way to accomplish this is by using the
address
attribute, described in Section 10.2.1 “Function Specifiers”. For example,
to locate function PrintString at address 0x8000 in program memory:
int
__
attribute
_ _
((address(0x8000))) PrintString (const char *s);
Another way to locate code is by placing the function into a user-defined section, and
specifying the starting address of that section in a custom linker script. This is done as
follows:
specifying the starting address of that section in a custom linker script. This is done as
follows:
1.
Modify the code declaration in the C source to specify a user-defined section.
2.
Add the user-defined section to a custom linker script file to specify the starting
address of the section.
address of the section.
For example, to locate the function PrintString at address 0x8000 in program
memory, first declare the function as follows in the C source:
memory, first declare the function as follows in the C source:
int _ _attribute_ _((_ _section_ _(".myTextSection")))
PrintString(const char *s);
The section attribute specifies that the function should be placed in a section named
.myTextSection
.myTextSection
, rather than the default .text section. It does not specify where
the user-defined section is to be located. That must be done in a custom linker script,
as follows. Using the device-specific linker script as a base, add the following section
definition:
as follows. Using the device-specific linker script as a base, add the following section
definition:
.myTextSection 0x8000 :
{
*(.myTextSection);
} >program
This specifies that the output file should contain a section named .myTextSection
starting at location 0x8000 and containing all input sections named.myTextSection.
Since, in this example, there is a single function PrintString in that section, then the
function will be located at address 0x8000 in program memory.
starting at location 0x8000 and containing all input sections named.myTextSection.
Since, in this example, there is a single function PrintString in that section, then the
function will be located at address 0x8000 in program memory.