Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

Using (non-inline) assembly in online compiler

Topic last updated 11 Oct 2010, by Andrea Zanelli. 1 reply
Igor Skochinsky
13 Dec 2009 . Edited: 13 Dec 2009

For the curious, here's a short howto:

1) Create or upload an assembly file making sure the file extension is .s
2) Online compiler uses RVCT so you need to use ARM syntax. For example:

AREA |.text|, CODE, READONLY
EXPORT my_func
my_func
   ADD R0, R1
   BX LR

3) In C code, use extern "C" to link to your function:

extern "C" int my_func(int x, int y);

4) If you need to distinguish between two mbed models (ARM7 vs Cortex-M3), you can use the compiler define:

IF :DEF:TARGET_LPC1768
  ; can use Thumb2 here
ELSE
  ; only ARMv4[T] instructions allowed
ENDIF

For an example, see my FFT Port: FFT.

Note that if you need to use just a couple of instructions, it's much better to use an intrinsic (if available) or a piece of inline assembly.

Andrea Zanelli
11 Oct 2010

Hi Igor, how can I convert from inline to non-inline .s?