On Sa, 2016-01-16 at 01:26 +0100, Simon Ameis wrote: > Am 14.01.2016 um 23:57 schrieb Marc Santhoff: > > On Do, 2016-01-14 at 21:33 +0100, Simon Ameis wrote: > >> In general I already know these documents; what I'm looking for is an > >> implementation of a busy wait, not how to use it. > >> For C/C++ it's easy to get the code files. But I don't know where to get > >> compiler built-in procedures for gcc or other language's compilers. > > If you want to write Pascal code and don not need nano seconds accuracy, > > you have no need to now compiler internals. Only use time values and the > > divider factors. > I don't talk of FPC compiler internals but of gcc compiler internals. > E.g. the C implementation uses a compiler specific procedure > __builtin_avr_delay_cycles; I can't find a source to get known how it is > inlined in the resulting assembler code. > Please see for reference: > https://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/AVR-Built_002din-Functions.html
Well, this is the fpc mailing list ... How about asking the gcc guys that question? You could also easily fetch the gcc source code and 'grep' it. $ cd gcc-src $ grep -r * "_builtin_avr_delay_cycles" And if that doesn't help, write a short C code snippet using that function and then call the compiler like this: $ arm-gcc -nostdinc -c -S yoursnippet.c That will leave the asm (.s or .S) file for you to look at. > >> For point 3 there is a very good explanation in German at > >> http://www.avr-asm-tutorial.net/avr_de/zeitschleifen/index.html. > >> > >> The wicked thing is the calculation of the cpu cycles. The C > >> implementation uses floating point arithmetics wich is evaluated at > >> compile time. It doesn't work with wait times which are calculated at > >> runtime. > > Why not use calculated constants? The compiler can evaluate simple > > arithmetics at compile time: > > > > const > > sclk = int(round(SYSTEM_CLOCK / 42)); > > > > The resulting number will be as close to the float value as possible. > FPC doesn't support floating point on AVR; thus no floating point > constants are allowed, even if they can be evaluated to an integer > expression at compile time. FPC obviously first checks types and then > does optimization on known types. > > Thus only this code is valid on AVR: > const > sclk = SYSTEM_CLOCK div 42; OK, good to know. > The question isn't how to calculate this but how to fit it into a word > boundary for function call without loosing required accuracy. I don't understand. Fitting in a word boundary would be done using a compiler switch in code, IIRC "{$align 2}" or similar. If that's true for function implementations isn't clear, I cannot image it is. If you want to use Assembler code in Pascal there is documentation in the programmers manual, chapter 3. -- Marc Santhoff <m.santh...@web.de> _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
