BSP and Device Driver Development Guide
The GNU linker has a command language to specify the image format. This
command language can be quite complicated but most of what is required
can be learned by careful examination of a well-documented example.
The following is a heavily commented version of the linker script
used with the the gen68340 BSP This file can be found at
$BSP340_ROOT/startup/linkcmds.
/*
* Specify that the output is to be coff-m68k regardless of what the
* native object format is.
*/
OUTPUT_FORMAT(coff-m68k)
/*
* Set the amount of RAM on the target board.
*
* NOTE: The default may be overridden by passing an argument to ld.
*/
RamSize = DEFINED(RamSize) ? RamSize : 4M;
/*
* Set the amount of RAM to be used for the application heap. Objects
* allocated using malloc() come from this area. Having a tight heap
* size is somewhat difficult and multiple attempts to squeeze it may
* be needed reducing memory usage is important. If all objects are
* allocated from the heap at system initialization time, this eases
* the sizing of the application heap.
*
* NOTE 1: The default may be overridden by passing an argument to ld.
*
* NOTE 2: The TCP/IP stack requires additional memory in the Heap.
*
* NOTE 3: The GNAT/RTEMS run-time requires additional memory in
* the Heap.
*/
HeapSize = DEFINED(HeapSize) ? HeapSize : 0x10000;
/*
* Set the size of the starting stack used during BSP initialization
* until first task switch. After that point, task stacks allocated
* by RTEMS are used.
*
* NOTE: The default may be overridden by passing an argument to ld.
*/
StackSize = DEFINED(StackSize) ? StackSize : 0x1000;
/*
* Starting addresses and length of RAM and ROM.
*
* The addresses must be valid addresses on the board. The
* Chip Selects should be initialized such that the code addresses
* are valid.
*/
MEMORY {
ram : ORIGIN = 0x10000000, LENGTH = 4M
rom : ORIGIN = 0x01000000, LENGTH = 4M
}
/*
* This is for the network driver. See the Networking documentation
* for more details.
*/
ETHERNET_ADDRESS =
DEFINED(ETHERNET_ADDRESS) ? ETHERNET_ADDRESS : 0xDEAD12;
/*
* The following defines the order in which the sections should go.
* It also defines a number of variables which can be used by the
* application program.
*
* NOTE: Each variable appears with 1 or 2 leading underscores to
* ensure that the variable is accessible from C code with a
* single underscore. Some object formats automatically add
* a leading underscore to all C global symbols.
*/
SECTIONS {
/*
* Make the RomBase variable available to the application.
*/
_RamSize = RamSize;
__RamSize = RamSize;
/*
* Boot PROM - Set the RomBase variable to the start of the ROM.
*/
rom : {
_RomBase = .;
__RomBase = .;
} >rom
/*
* Dynamic RAM - set the RamBase variable to the start of the RAM.
*/
ram : {
_RamBase = .;
__RamBase = .;
} >ram
/*
* Text (code) goes into ROM
*/
.text : {
/*
* Create a symbol for each object (.o).
*/
CREATE_OBJECT_SYMBOLS
/*
* Put all the object files code sections here.
*/
*(.text)
. = ALIGN (16); /* go to a 16-byte boundary */
/*
* C++ constructors and destructors
*
* NOTE: See the CROSSGCC mailing-list FAQ for
* more details about the "[......]".
*/
__CTOR_LIST__ = .;
[......]
__DTOR_END__ = .;
/*
* Declares where the .text section ends.
*/
etext = .;
_etext = .;
} >rom
/*
* Exception Handler Frame section
*/
.eh_fram : {
. = ALIGN (16);
*(.eh_fram)
} >ram
/*
* GCC Exception section
*/
.gcc_exc : {
. = ALIGN (16);
*(.gcc_exc)
} >ram
/*
* Special variable to let application get to the dual-ported
* memory.
*/
dpram : {
m340 = .;
_m340 = .;
. += (8 * 1024);
} >ram
/*
* Initialized Data section goes in RAM
*/
.data : {
copy_start = .;
*(.data)
. = ALIGN (16);
_edata = .;
copy_end = .;
} >ram
/*
* Uninitialized Data section goes in ROM
*/
.bss : {
/*
* M68K specific: Reserve some room for the Vector Table
* (256 vectors of 4 bytes).
*/
M68Kvec = .;
_M68Kvec = .;
. += (256 * 4);
/*
* Start of memory to zero out at initialization time.
*/
clear_start = .;
/*
* Put all the object files uninitialized data sections
* here.
*/
*(.bss)
*(COMMON)
. = ALIGN (16);
_end = .;
/*
* Start of the Application Heap
*/
_HeapStart = .;
__HeapStart = .;
. += HeapSize;
/*
* The Starting Stack goes after the Application Heap.
* M68K stack grows down so start at high address.
*/
. += StackSize;
. = ALIGN (16);
stack_init = .;
clear_end = .;
/*
* The RTEMS Executive Workspace goes here. RTEMS
* allocates tasks, stacks, semaphores, etc. from this
* memory.
*/
_WorkspaceBase = .;
__WorkspaceBase = .;
} >ram
}
BSP and Device Driver Development Guide
Copyright © 1988-2008 OAR Corporation