driverlib speed anomaly (_ROM) (TIVA TM4C123GXL)

[madias 0]

Hello,

after fooling around a little bit, I recognize following driverlib behavior:

 

While I get with this sketch about 450kHz on  my oscilloscope

 

#include <stdint.h>
#include <stdbool.h>


#define PART_TM4C123GH6PM
#include "inc/tm4c123gh6pm.h"
#include "driverlib/gpio.h"
byte running=1;
void setup()
{
  GPIOPadConfigSet(GPIO_PORTA_BASE, 0xff, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD);
  GPIODirModeSet (GPIO_PORTA_BASE, 255, GPIO_DIR_MODE_OUT);
}


void loop()
{
  while(1)
  {
  running=!running;
  GPIOPinWrite(GPIO_PORTA_BASE,128,running<<7);
  }} 

...I'll get only 176kHz with the ROM_ equivalent:

 

#include <stdint.h>
#include <stdbool.h>


#define PART_TM4C123GH6PM
#include "inc/tm4c123gh6pm.h"
#include "driverlib/gpio.h"
byte running=1;
void setup()
{
  ROM_GPIOPadConfigSet(GPIO_PORTA_BASE, 0xff, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD);
  ROM_GPIODirModeSet (GPIO_PORTA_BASE, 255, GPIO_DIR_MODE_OUT);
}


void loop()
{
  while(1)
  {
  running=!running;
  ROM_GPIOPinWrite(GPIO_PORTA_BASE,128,running<<7);
  }
}

Does anyone have any idea why is that?

Remember, that all energia stuff is related to the ROM_* commands (like wiring_digital.c)

 

 

[madias 0]

Ok, it seems, that my DS201 is out of range for this measure, can someone check this two codes out with "real equipment"?

Meanwhile I've stripped the code down to complete low level: (Measuring pin is PA7)

 

#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_gpio.h"
#define PART_TM4C123GH6PM
#include "inc/tm4c123gh6pm.h"
#include "driverlib/gpio.h"
byte running=1;
void setup()
{
  GPIOPadConfigSet(GPIO_PORTA_BASE, 0xff, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD);
  GPIODirModeSet (GPIO_PORTA_BASE, 255, GPIO_DIR_MODE_OUT);
}


void loop()
{
  while(1)
  {
  running=!running;
  HWREG(0x40004200)=running<<7;
  }
}

[pabigot 355]

This thread shows how to measure the duration of a code sequence using the cycle timer. That's probably the best solution for comparisons like this: read the cycle counter, run the loop for N iterations, then read it again and figure out the speed.