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???
03/07/09 19:16
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 		 #163210 - Actually, I found the for loop faster.
Responding to: ???'s previous message
I read you comments and tried the while loop.

The ARM Real View compiler was fastest with using the loop counter. Comparing the end pointer involved two LOADs. So my best effort was 43 us. But the "revised" problem was to do a single value in 60ns.

There are obviously several Compiler vendors out there, and several different ASM codes will be generated. The Keil CA compiler does not compete at all.

I regard this as fairly academic anyway. I just look at a compiler as a translation tool. Functionality is more important than raw efficiency. It is seldom that this matters.

Obviously I would side with Richard if it comes to squeezing the last nanosecond out of an application. Assembler will ensure the exact instruction sequence. However as a general rule, a program should be equally functional irrespective of the Compiler and hopefully the platform that it runs on.

It appears that Richard's trick is to sniff the external address bus with some external hardware. A clever idea, but not exactly cricket. ( at least in terms of a language specification ) As I implied in a previous post, this is a side-effect. If you were to ask me, I would prefer an AUXRAM operation to not place stuff on an external bus. After all AUXRAM is an internal resource, and why should we waste ports on an internal operation?

Again, I should qualify my comments by saying that I am neither a 8051 or ARM expert.

David.


List of 76 messages in thread
TopicAuthorDate
NXP P89LPC936 Auxilary RAM            01/01/70 00:00      
   Compiler Cannot Save the Day At Runtime            01/01/70 00:00      
      I found it.....            01/01/70 00:00      
         Incorrect!            01/01/70 00:00      
            To be fair,...            01/01/70 00:00      
               Its good info to know...            01/01/70 00:00      
   how is it done in C?            01/01/70 00:00      
   Maybe you should try doing it ASM!            01/01/70 00:00      
      You should start a new thread on that!            01/01/70 00:00      
      Not in this case!            01/01/70 00:00      
         A compiler should support ALL MCU features ...            01/01/70 00:00      
            A compiler should translate the language            01/01/70 00:00      
               Still C - just not strict.            01/01/70 00:00      
            I didn't say that!            01/01/70 00:00      
               It is not that clean and clear            01/01/70 00:00      
                  Deviants are deviant            01/01/70 00:00      
                     Keil and SDCC need no macros ...            01/01/70 00:00      
                        Are you sure?            01/01/70 00:00      
                     That's probably correct, but ...            01/01/70 00:00      
                        A C compiler can map the hardware quite well            01/01/70 00:00      
                           compiler vendors are looking at the new processors            01/01/70 00:00      
                              I once mentioned that ...            01/01/70 00:00      
                           It's not what I'd choose, but it is a matter of perefernce            01/01/70 00:00      
                              As flash gets bigger, the code steps do too.            01/01/70 00:00      
                              Still not needed for other architectures            01/01/70 00:00      
                                 We will have to agree to disagree ... I guess            01/01/70 00:00      
                                    Which single-clocker is cheaper than an ARM?            01/01/70 00:00      
                                       RE: Which single-clocker is cheaper than an ARM?            01/01/70 00:00      
                                       differs considerably from the classic microcontroller?            01/01/70 00:00      
                                       Horses for courses            01/01/70 00:00      
                                          Always start each project by scanning the market            01/01/70 00:00      
                                             On that we can agree            01/01/70 00:00      
                                          Maybe, but what are they comparing?            01/01/70 00:00      
                                             Did you actually look?            01/01/70 00:00      
                                                Yes, I did.            01/01/70 00:00      
                                       it's a tradeoff            01/01/70 00:00      
                                          Is it 2006 already?            01/01/70 00:00      
                                             Really?            01/01/70 00:00      
                                                that's outright silly            01/01/70 00:00      
                                                   Maybe ... which is why it is not yet the case            01/01/70 00:00      
                                                      the eyes of the beholder            01/01/70 00:00      
                                                         Look at it from another viewpoint for a moment            01/01/70 00:00      
                                          RE: I'm not the one to ask about IC prices            01/01/70 00:00      
                                             doesn't mean I'm totally in the dark            01/01/70 00:00      
                                                Richard Erlacher has left the planet            01/01/70 00:00      
                                                   Maybe Andy's the one who's lost            01/01/70 00:00      
                                                      I cannot believe you even looked at ARM            01/01/70 00:00      
                                                         It's all relative            01/01/70 00:00      
                                                            Price doesn't directly follow processor size            01/01/70 00:00      
                                                            What about performance?            01/01/70 00:00      
                                                         Be specific please.            01/01/70 00:00      
                                                            You can use your own supplier            01/01/70 00:00      
                                                               Your test simulates as 41.04us            01/01/70 00:00      
                                                                  RE: ARM compiles do not like byte-addressing            01/01/70 00:00      
                                                                     A typo on my part            01/01/70 00:00      
                                                                        Case of full unroll            01/01/70 00:00      
                                                                           ... and what does THAT ARM MCU cost?            01/01/70 00:00      
                                                                              WHO CARES            01/01/70 00:00      
                                                                                 Absolutely true!            01/01/70 00:00      
                                                                              $5 or lower            01/01/70 00:00      
                                                                                 My Simulation times were wrong.            01/01/70 00:00      
                                                                                    67% of your loop was your loop            01/01/70 00:00      
                                                                                    re-written the loop in C            01/01/70 00:00      
                                                                                       Try without loop counter            01/01/70 00:00      
                                                                                          You're right!            01/01/70 00:00      
                                                                                             Similar trick with ARM7 would require 66.67MHz            01/01/70 00:00      
                                                                                             60ns with no store instruction.            01/01/70 00:00      
                                                                                                25% speedup            01/01/70 00:00      
                                                                                                   Actually, I found the for loop faster.            01/01/70 00:00      
                                                                                                      Compiler setting?            01/01/70 00:00      
                                                                                                         I made NO optimisation            01/01/70 00:00      
                                                                                                            Avoid variable aliasing if you like high optimization levels            01/01/70 00:00      
                                                                                                               The RealView compiler is very competent            01/01/70 00:00      
                                                                                                                  Yes, caching            01/01/70 00:00      
                                                                                                                  Yes, caching            01/01/70 00:00      
                                                                                                It's much easier with the 8-bit single-clocker            01/01/70 00:00      

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