#16234 - x86asm - Wed Feb 11, 2004 1:37 am
Hi, I'm surprised at how easy ARM7 assembly is, I would like to try and use it along with C, just to try programming an embedded system. I have a few questions (I use VisualHAM) and prefer to use external ASM files (less red tape)
1. How do I declare say a 32-bit variable in an ASM source file, I tried .DCD but didnt work for me :*(
2. How would I reference external variables in C source files (using the .EXTERN keyword?)
3. How do you get the C compiler to compile THUMB code instead of ARM code?
These are the only two stumbling blocks I have come across (kind of embarassing actually :) ), but with your guys help I can get back on track.
_________________
Hello Everyone :D
#16240 - poslundc - Wed Feb 11, 2004 3:04 am
| x86asm wrote: |
Hi, I'm surprised at how easy ARM7 assembly is, I would like to try and use it along with C, just to try programming an embedded system. I have a few questions (I use VisualHAM) and prefer to use external ASM files (less red tape)
1. How do I declare say a 32-bit variable in an ASM source file, I tried .DCD but didnt work for me :*( |
Declare a label where you want your variable, then use the .word directive. Check out the GAS ARM asm reference (downloadable from http://re-eject.gbadev.org/) for a bunch of other directives.
| Quote: |
| 2. How would I reference external variables in C source files (using the .EXTERN keyword?) |
| Code: |
ldr r0, GLOBALS @ r0 <- pointer to myCVariable
ldr r0, [r0] @ r0 <- myCVariable
GLOBALS:
.word myCVariable |
| Quote: |
| 3. How do you get the C compiler to compile THUMB code instead of ARM code? |
Use the -mthumb command-line switch when calling gcc with your input files. To write Thumb code in assembler, precede your code with the .thumb directive.
Cheers,
Dan (did I win?).
#16242 - torne - Wed Feb 11, 2004 3:17 am
One further thing to remember: if you want to be able to call thumb from ARM and vice versa, then all your C modules need to be compiled with -mthumb-interwork, and you must use interworking return sequences in your assembly code. Read the ARM/Thumb procedure call standard (and previous posts in this forum) for details.
#16296 - x86asm - Wed Feb 11, 2004 10:49 pm
| poslundc wrote: |
| x86asm wrote: | Hi, I'm surprised at how easy ARM7 assembly is, I would like to try and use it along with C, just to try programming an embedded system. I have a few questions (I use VisualHAM) and prefer to use external ASM files (less red tape)
1. How do I declare say a 32-bit variable in an ASM source file, I tried .DCD but didnt work for me :*( |
Declare a label where you want your variable, then use the .word directive. Check out the GAS ARM asm reference (downloadable from http://re-eject.gbadev.org/) for a bunch of other directives.
| Quote: | | 2. How would I reference external variables in C source files (using the .EXTERN keyword?) |
| Code: | ldr r0, GLOBALS @ r0 <- pointer to myCVariable
ldr r0, [r0] @ r0 <- myCVariable
GLOBALS:
.word myCVariable |
| Quote: | | 3. How do you get the C compiler to compile THUMB code instead of ARM code? |
Use the -mthumb command-line switch when calling gcc with your input files. To write Thumb code in assembler, precede your code with the .thumb directive.
Cheers,
Dan (did I win?). |
I what you suggested and it worked, but trying it in VisualHAM's debugger, it crashes with illegal instruction, I guess I need to jump somewhere cause its trying to execute what is in the variable. Thanks alot posluns, explains alot ;)
_________________
Hello Everyone :D
#16297 - poslundc - Wed Feb 11, 2004 11:18 pm
Yeah, you need to stick your variables somewhere close enough to your code that they can be referenced local to the program counter but still somewhere they won't get executed. :P
So usually that means sticking them after the end of a function or routine, after you bx lr.
Dan.
#16348 - x86asm - Fri Feb 13, 2004 2:18 am
| poslundc wrote: |
Yeah, you need to stick your variables somewhere close enough to your code that they can be referenced local to the program counter but still somewhere they won't get executed. :P
So usually that means sticking them after the end of a function or routine, after you bx lr.
Dan. |
Hey thats fixes everything thanks a bunch! BTW, I'm a high school student looking to enter the software programming field and I noticed that on your page you were educated at McMaster U, how was it there and how is the software programming job market here in Toronto?
Thanks ;)
_________________
Hello Everyone :D
#16352 - poslundc - Fri Feb 13, 2004 3:05 am
| x86asm wrote: |
| BTW, I'm a high school student looking to enter the software programming field and I noticed that on your page you were educated at McMaster U, how was it there and how is the software programming job market here in Toronto? |
Ugh, you don't want to know... :P Go to college instead and maybe get yourself a real job. Or not. It depends on what you're interested in doing, I guess.
If you really want to know the ugly details, send me an e-mail and I'll relate it to you.
Dan.