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This FAQ is intended to list a number of questions that arise quite
often.
Note:Feel free to send suggestions and new FAQ entries.
- Is S19 format supported?
- S19 and Intel Hex records are supported for many many years by
the GNU Binutils. They are not the native format because they do
not provide all the information that a linker and a debugger
need (symbols, relocation, debug information).
- How can I generate S19 files?
- There are two ways to generate S19 files:
- How can I migrate assembly sources to GNU as?
- Use the --mri option of GNU as. This option enables
a kind of compatibility mode with Motorola Assembly Language
Specification. There are however a few restrictions:
- The ORG command is not supported. Replace
them with a definition of a section (section name).
- Single quote strings are not supported (CVS Binutils only).
- What is the crt0 and how can I remove it?
- The startup file crt0 is used to initialize the stack,
install the data section (initialized variables), clear the bss
section (uninitialized global and static variables), prepare
and jump to the main. The startup file is automatically
linked at beginning of each program. It is possible to avoid
to use the default crt0 by doing the following:
- Write your own startup code. This can be written in C
or in assembly. The entry point should be named
_start.
- Pass the -nostartfiles option to m6811-elf-gcc
during the final link. This option suppresses the link
with the crt0 file.
- How can I inline assembly in C?
- Gcc allows you to inline assembly within C source code. The assembly
instruction can have input and output parameters to interact
with the C code. An inline assembly without arguments is written
as follows:
asm volatile ("cli");
The volatile keyword is optional. It tells Gcc not to
optimize the instruction by not removing or changing its place
within the code. It is more than recommended to use it.
Input and output parameters are specified by constraints.
The constraint is a string that indicates the characteristics of
the operand in terms of constant, register, memory
and so on. The output operands are listed first and introduced
by =. The following instruction:
asm volatile ("tpa\n\tsei" : "=d"(mask));
defines an output operand that is read from register d
and put in the local variable named mask.
A more complete description about the asm mechanisms is presented
in the following sections:
- What is the memory.x?
- This file is used when you use the m68hc11elfb linker script.
It defines memory banks that tells the linker where to put the
text, data and other sections. A typical memory.x file
defines the MEMORY banks as follows:
MEMORY
{
page0 (rwx) : ORIGIN = 0x0, LENGTH = 256
text (rx) : ORIGIN = 0xE000, LENGTH = 2048
data : ORIGIN = 0x0, LENGTH = 0
}
- How does the linker know where memory.x is?
- The memory.x is searched in the current directory and in all the
directories specified with the -L option.
There is also a default directory which is /usr/m6811-elf/lib
or xxx\m6811-elf\lib.
- How can I setup an interrupt table for a ROM?
- A special section exists for the definition of the interrupt
vector table of the 68HC11 or 68HC12. The vectors must be in a
section named .vectors.
In assembly, use:
.sect .vectors
With gcc, use:
__attribute__ ((section (".vectors")))
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