[avr-gcc-list] Problem with delay loop

Hi all, In the latest WinAVR (avr-gcc (GCC) 4.1.2 (WinAVR 20070525) I found this. Check this out: //== void delay(unsigned del_cnt) { while(del_cnt--); return; } //=== Compiles as (from the .lss file): //=== void

RE: [avr-gcc-list] Problem with delay loop

> -Original Message- > From: > [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] > org] On Behalf Of David Brown > Sent: Friday, September 28, 2007 3:17 AM > To: AVR-GCC > Subject: Re: [avr-gcc-list] Problem with delay loop > > > This is probably in the FAQ somewhere - if not, it should be!

Re: [avr-gcc-list] Problem with delay loop

I think we are discussing not the solution :-) The compiler optimizes unused code away, that is OK! If we use a volatile, the WRITE ACCESS could not longer be optimized and also a new READ ACCESS before subtraction must! be done. That is what the compiler do, that is also OK! If there is a "loc

Re: [avr-gcc-list] Problem with delay loop

Royce Pereira wrote: So I have to write more 'C' code :) to get the same stuff done, in the 'new & smarter' compiler! Not more code, just correct code. Have you tried returning the final value of your delay argument from the function? If the compiler optimizes only within the boundaries of

Re: [avr-gcc-list] Problem with delay loop

On Fri, Sep 28, 2007 at 09:05:40AM -0500, David Kelly wrote: > > For finer delays don't forget the OCR functions on the timers. Is pretty > easy to write and create very accurate delays with: > > void delay( uint8_t delay ); > { > OCR2A = TCNT2 + delay; > TIFR2 = (1< > // wait

Re: [avr-gcc-list] Problem with delay loop

Please use optimizer! Something like -O2 -O3 -Os ... as you need! Simplify your delay loop: void delay(volatile word cnt) { ... Have fun! Royce Pereira schrieb: Hi, On Fri, 28 Sep 2007 14:47:26 +0530, David Brown <[EMAIL PROTECTED]> wrote: This is probably in the FAQ somewhere - if not, it

Re: [avr-gcc-list] Problem with delay loop

Hi, On Fri, 28 Sep 2007 14:47:26 +0530, David Brown <[EMAIL PROTECTED]> wrote: > > This is probably in the FAQ somewhere - if not, it should be! > > The compiler is smart enough to figure out that your delay function does > no useful work - thus the optimiser does not generate any code. This is

Re: [avr-gcc-list] Problem with delay loop

Hi, On Fri, 28 Sep 2007 14:47:26 +0530, David Brown <[EMAIL PROTECTED]> wrote: > > This is probably in the FAQ somewhere - if not, it should be! > > The compiler is smart enough to figure out that your delay function does > no useful work - thus the optimiser does not generate any code. This is >

Re: [avr-gcc-list] Problem with delay loop

Hi, On Fri, 28 Sep 2007 13:42:18 +0530, Klaus Rudolph <[EMAIL PROTECTED]> wrote: > The code has been optimized. Well done! > If you need the variable access use 'volatile' > Why does it get optimised? I understand the meaning of 'volatile', but why is it required here ? It is clear that the varia

Re: [avr-gcc-list] Problem with delay loop

Royce Pereira schreef: Hi all, In the latest WinAVR (avr-gcc (GCC) 4.1.2 (WinAVR 20070525) I found this. Check this out: //== void delay(unsigned del_cnt) { while(del_cnt--); return; } //=== Well writing your own delay_loops is n

Re: [avr-gcc-list] Problem with delay loop

The code has been optimized. Well done! If you need the variable access use 'volatile' Hi all, In the latest WinAVR (avr-gcc (GCC) 4.1.2 (WinAVR 20070525) I found this. Check this out: //== void delay(unsigned del_cnt) { while(del_cnt--); return; } //

Re: [avr-gcc-list] Problem with delay loop

On Fri, Sep 28, 2007 at 01:29:19PM +0530, Royce Pereira wrote: > Hi all, > > In the latest WinAVR (avr-gcc (GCC) 4.1.2 (WinAVR 20070525) I found this. > > Check this out: > //== > void delay(unsigned del_cnt) > { >while(del_cnt--); > >return; > } > //=

Re: [avr-gcc-list] Problem with delay loop

This is probably in the FAQ somewhere - if not, it should be! The compiler is smart enough to figure out that your delay function does no useful work - thus the optimiser does not generate any code. This is correct compilation - it's your code that is wrong. The difference is that the newer

RE: [avr-gcc-list] Problem with delay loop

> Date: Fri, 28 Sep 2007 14:21:38 +0530> To: [EMAIL PROTECTED]> Subject: Re: > [avr-gcc-list] Problem with delay loop> From: [EMAIL PROTECTED]> CC: > AVR-GCC-list@nongnu.org> > Hi,> > On Fri, 28 Sep 2007 13:42:18 +0530, Klaus > Rudolph <[EMAIL PROTECTED]> wrote:> > > The code has been optimized

Re: [avr-gcc-list] Problem with delay loop

Hi Klaus, On Fri, 28 Sep 2007 14:57:14 +0530, Klaus Rudolph <[EMAIL PROTECTED]> wrote: > Please use optimizer! Something like -O2 -O3 -Os ... as you need! My makefile already has OPT = s > > Simplify your delay loop: > void delay(volatile word cnt) { ... > Already tried that. No change. If it's

Re: [avr-gcc-list] Problem with delay loop

Hi all, OK fine I agree. we have to use 'volatile' and all. But why must it generate such horrid code... (I reproduce the comparison again below to get the *real* issue into focus) The compiler output with the 'correct' code ('volatile' used): //-

Re: [avr-gcc-list] Problem with delay loop

On Fri, Sep 28, 2007 at 11:26:43PM +0530, Royce Pereira wrote: > Hi all, > > OK fine I agree. > > we have to use 'volatile' and all. > > But why must it generate such horrid code... There are those here who would tell you that any calibrated delay loop is horrible code. The stack has to be pro

Re: [avr-gcc-list] Problem with delay loop

David Kelly wrote: ... because it was volatile it *had* to be fetched and stored each time. Oh boy. That's a really interesting statement (to me anyway, but I have a volatile fetish). You're saying that having chosen to put the variable in memory, the compiler is obliged to fetch it prior t

Re: [avr-gcc-list] Problem with delay loop

On Sep 28, 2007, at 8:58 PM, Graham Davies wrote: David Kelly wrote: ... because it was volatile it *had* to be fetched and stored each time. Oh boy. That's a really interesting statement (to me anyway, but I have a volatile fetish). You're saying that having chosen to put the variable