OSCPUUsage higher than 100?

Altera_Forum · ‎10-10-2013

I wanted to measure maximal and average CPU usage in my design by checking the global variable OSCPUUsage. Therefore, I made a simple application containing 3 tasks doing some dummy array reading/writing/copying + one main task that displays CPU load values on a LCD screen. I use an INK board with MicroC/OS-II.

The trouble is that the maximal CPU usage value is higher than 100! While debugging the design and putting a breakpoint inside OSTaskStat, I can see that the first non-zero value of OSCPUUsage is higher than 100. All the next values calculated in this task are much lower.

My questions are: what causes such high OSCPUUsage values? Should I change the measurement method I use or treat it as a mistake?

#include <stdio.h># include "includes.h"# include "system.h"# include "altera_avalon_lcd_16207_regs.h"# include "altera_avalon_pio_regs.h"
/* Definition of Task Stacks */# define   TASK_STACKSIZE       2048
OS_STK      task0_stk;
OS_STK    task1_stk;
OS_STK    task2_stk;
OS_STK      task3_stk;
/* Definition of Task Priorities */# define TASK0_PRIORITY      1# define TASK1_PRIORITY      2# define TASK2_PRIORITY      3# define TASK3_PRIORITY      4
/*Adjustable parameters*/# define ARRAY_NUM 2000# define DELAY_MS 200 //delay of the task that displays OSCPUUsage on LCD screen# define AVG_SAMPLES 100
/* SRAM data */
int CopyArray1 ;
int CopyArray2 ;
/*CPU load statistics*/
int CPUUsageMax=0;
int CPUUsageAvg=0;
int CPUUsageSum=0;
int CPUUsageDiv=0;
/*Task prototypes*/
void task0 (void* pdata);
void task1 (void* pdata);
void task2 (void* pdata);
void task3 (void* pdata);
FILE* lcd;
void task0(void*pdata)
{
        OSStatInit();
        OSTaskCreateExt(task1, NULL, &task1_stk,
                TASK1_PRIORITY, TASK1_PRIORITY, task1_stk, TASK_STACKSIZE, NULL, 0);
        OSTaskCreateExt(task2, NULL, &task2_stk,
                TASK2_PRIORITY, TASK2_PRIORITY, task2_stk, TASK_STACKSIZE, NULL, 0);
        OSTaskCreateExt(task3, NULL, &task3_stk,
                TASK3_PRIORITY, TASK3_PRIORITY, task3_stk, TASK_STACKSIZE, NULL, 0);
      while(1)
      {
          IOWR_ALTERA_AVALON_PIO_DATA(APPL_SUBSYSTEM_PIO_LED_RED_BASE, 0x1);
          //Display the maximal CPU usage and the average CPU usage from last AVG_SAMPLES measurements
          if (OSCPUUsage>CPUUsageMax)
          {
//Maximal CPU usage:
              CPUUsageMax=OSCPUUsage;
          }
          if (CPUUsageDiv>=AVG_SAMPLES)
//Average value of (AVG_SAMPLES) samples:
          {
              CPUUsageDiv=0;
              CPUUsageSum=0;
              CPUUsageAvg=0;
          }
          else
          {
              CPUUsageDiv++;
              CPUUsageSum+=OSCPUUsage;
              CPUUsageAvg=CPUUsageSum/CPUUsageDiv;
          }
          fprintf(lcd, "Max:%u Avg:%u \n", CPUUsageMax, CPUUsageAvg);
          OSTimeDlyHMSM(0, 0, 0, DELAY_MS);
      }
}
int main(void)
{
  IOWR_ALTERA_AVALON_PIO_DATA(APPL_SUBSYSTEM_PIO_LED_RED_BASE, 0x0);
  lcd = fopen(APPL_SUBSYSTEM_LCD_NAME, "w");
  OSInit();
  OSTaskCreateExt(task0, NULL, &task0_stk,
          TASK0_PRIORITY, TASK0_PRIORITY, task0_stk, TASK_STACKSIZE, NULL, 0);
  OSStart();
  fclose(lcd);
  return 0;
}
void task1(void* pdata)
{
  while (1)
  {
    for (int i=0;i<ARRAY_NUM;i++)
    {
        //Some array operations performed just to check the CPU load
        CopyArray1=1;
        CopyArray2=CopyArray1;
        (void) CopyArray2;
    }
//Sanity check: blinking LEDs
    IOWR_ALTERA_AVALON_PIO_DATA(APPL_SUBSYSTEM_PIO_LED_RED_BASE, 0x2);
    OSTimeDlyHMSM(0, 0, 0, 100);
  }
}
void task2(void* pdata)
{
  while (1)
  {
    for (int i=0;i<ARRAY_NUM;i++)
    {
        CopyArray1=2;
        CopyArray2=CopyArray1;
        (void) CopyArray2;
    }
    IOWR_ALTERA_AVALON_PIO_DATA(APPL_SUBSYSTEM_PIO_LED_RED_BASE, 0x4);
    OSTimeDlyHMSM(0, 0, 0, 10);
  }
}
void task3(void*pdata)
{
  while (1)
  {
    for (int i=0;i<ARRAY_NUM;i++)
    {
        CopyArray1=3;
        CopyArray2=CopyArray1;
        (void) CopyArray2;
    }
    IOWR_ALTERA_AVALON_PIO_DATA(APPL_SUBSYSTEM_PIO_LED_RED_BASE, 0x8);
    OSTimeDlyHMSM(0, 0, 0, 1);
  }
}

BR,

Nathalie