Hi all,
I wana read a 20Mhz ADC data by AT91SAM7S128,I read about Atmel I/Os MaxFrequency but when i write code to set and clear an I/O pin continual in a while loop,its toggle speed just reached to 6 7 MHz!
now i wonder what's the 25Mhz maxspeed that mentioned in its datasheet? how we can reach to that toggle frequency?

thanks,
best regards,
pepe.

another question:

how do we set VDDIO (options are 3.3V or 1.8V)?


The 25MHz speed applies to PA[16...4] and PA[31...21] at 3.3V VDDIO.

Hi pepe,

I've made a lot of tests that I think it could be of your interest. What I saw is that there is a big difference using Atmel library for setting the pin output versus using a direct assignment to the register.

If you use GCC, you will see also that Optimizations Levels and Parameters play a big role in the toggle frequency. I've made the measurements with an Agilent Logic Analyzer. My board is an AT91SAM7S-EK.

• Using Atmel library
  
  • Code:
    
    Code:
    #define PINO {1 << 3, AT91C_BASE_PIOA, AT91C_ID_PIOA, PIO_OUTPUT_1, PIO_DEFAULT}
    const Pin pino[] = { PINO };
    while(1){
       PIO_Clear(pino);
       PIO_Set(pino);
    }
  • Results:
    No Compiler Optimization
    Period: 1860ns (538kHz)
    Duty Cycle: 960/1860 = 52%
    
    
    
• Writing straight to register
  
  • Code:
    
    Code:
    volatile unsigned int *PIO_SODR = (unsigned int *)0xFFFFF430;
    volatile unsigned int *PIO_CODR = (unsigned int *)0xFFFFF434;
    while(1){
       *PIO_CODR = 8;
       *PIO_SODR = 8;
    }
  • Results:
    No Compiler Optimization
    Period: 340ns (2.94MHz)
    Duty Cycle: 200/340 = 59%
    
    
    
• Highly optimized
  
  • Writing straight to register
  • compiler parameters: -O1 -funroll-all-loops -fomit-frame-pointer
  • Results:
    Period: 125ns (8.00MHz)
    Duty Cycle: 65/125 = 52%
    
    In this test, for each 8 cycles, one had 187ns period. That give us an average of 7.67MHz.
    Running from flash drops toggle frequency to 6MHz (5.68MHz average).

I think results still can be optimized a lot, if you write code in assembly and if you use other compiler parameters (assembler parameters in this case).

A good reference: Optimization in GCC.



Regards,

Furuya