Lpc2000

--- In lpc2000@yahoogroups.com, "ah_sandiego" <ah_sandiego@...> wrote:
>
> Can someone post a simple example of C and inline ASM in a single 
> file. I use the LPC2148 but any LPC board example would be helpful.
> 
> Thanks,
> AH
>
Depending on the compiler optimization levels, inline asm has minimal 
benefit for size or speed.  Inline asm also limits portability for 
hardware and compilers. Even if you think it will never be an issue...

What are you goals for this? A few bytes? A save a bit of time- 50ns? 
100ns? Access to a hardware specific feature or registers? It will be 
difficult to beat the compiler for speed and/or density.  The ARM was 
designed for compilers and the compilers are very good at 
optimization.  

There are several good 'c' solutions but it really depends on what 
you are doing. "Function Inlining" (check your compiler options) will 
avoid the timer overhead of calling a function.  

This is from the IAR C reference:
"Function inlining means that a simple function, whose definition is 
known at compile time, is integrated into the body of its caller to 
eliminate the overhead of the call. This optimization, which is 
performed at optimization level High, normally reduces execution 
time, but increases code size. The resulting code might also be 
difficult to debug."

If it is execution speed you are after, time the C function with a 
some io bit toggling either side of the call with an oscilloscope.  
Then add up the execution time of your hand written instructions and 
compare.*  Expect better results from the compiler code.

If it is size, compare the size of the C function in the map file 
with the size of your hand written code.*

If it is access to the hardware, use the compiler extensions or 
pragma. 

*(both of these techniques introduce some inaccuracy but the results 
will be close. Let's not start a debate on the finer points of 
measurement) 

~Ian