AVR-Chat

perhaps it is possible to use AVR i'll try it .i made a up/down counter by a mega16 for counting an encoder it was 2048 pulse when i rotate it slowly there was no any problem but when i rotate it over 500rpm it lost some pulses finally i made it by TTL ICs and now it work at 11000rpm.AVRs isnot fast enough for this project.
i want to make a position loop (like cnc machine) i already tried it by a mega16 i could not be successful the motor start to shake when the axis arrived to the destination. perhaps the last loop in program which check the position is too long and if i improve the program the motor would shake less, any way if i use faster controller it will work properly.in some servo drives like Fanuc and Mitsubishi is used DSPs like TMS320C25 for positioning control they are very fast but  expensive
--- On Wed, 8/22/12, Tim Mitchell <tim@sabretechnology.co.uk> wrote:

From: Tim Mitchell <tim@sabretechnology.co.uk>
Subject: RE: [AVR-Chat] Re: fast controller
To: AVR-Chat@yahoogroups.com
Date: Wednesday, August 22, 2012, 8:23 PM
















 



  


    
      
      
      ----Original Message----

From: AVR-Chat@yahoogroups.com

[mailto:AVR-Chat@yahoogroups.com] On Behalf Of bonzadog

Sent: 22 August 2012 15:59 To: AVR-Chat@yahoogroups.com

Subject: Re: [AVR-Chat] Re: fast controller



> Could you please give an example. I do find it hard to

> believe a 100Mhz 

> system is being overperformed by a

> much lower speed 16Mhz. Perhaps the HW (UI,UART,CAN etc) 

> on the 16Mhz 

> is perhaps faster or offers more

> possibilities?



OK - the task was to pulse width modulate a number of LEDs in software by wiggling pins, while receiving serial data commands. I was surprised to find that the AVR can do 8 bit PWM faster. In fact in many bit-twiddling applications you can get better speed out of an AVR.



I came to the conclusion it was mostly down to the instruction pipelining on the ARM devices which is very inefficient when jumping around code (I was using an ARM7 device, the Cortex-M3 devices are better). Basically every time you do a jump it wastes 6 cycles loading the next instruction. Also the AVR port bit set/clear instructions only take 1 cycle whereas the ARM takes 4 or 6.



If the PWM is more than 8 bit then the ARM was faster (just).



-- 

Tim Mitchell





    
     

    
    






  










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