CodeWarrior for MCU中的主题 Re: How make a delay?

How make a delay?

PedroM — Mon, 20 Dec 2010 22:33:16 GMT

Hello,

I´m beginner programmer with MC9RS08KA in C, and would like to help to create a delay of 700ms. e.g. After press a button, one led turn on after 700ms. I knew the function delay_ms() used in PICs, but I don't know how make with codewarrior. Anyone know?

tks.

Re: How make a delay?

Lundin — Mon, 20 Dec 2010 22:57:21 GMT

The professional way is to use one of the on-chip timers or the RTC (real time clock). You'll have to read about those in the manual.

The hobbyist way is to burn away all CPU capacity in a counting loop with a volatile counter variable. You will have to disassemble the code and count the instructions and their cycles, or alternatively write the function in assembler.

The same for contact debouncing: you will have to debounce the button with a timer, no matter if you are using Freescale or PIC.

Re: How make a delay?

bigmac — Wed, 22 Dec 2010 12:29:15 GMT

Hello, and welcome to the forum.

The 'RS08KA8 device has two timer modules, a MTIM and a TPM. Either could be used to generate a delay of 700ms. I will explain a possible approach using the MTIM module.

Since the 'RS devices do not have a proper interrupt capability, you will need to poll for the occurrence of MTIM overflow. Depending on your requirements, you could generate the delay in one 700ms increment, or alternatively in a number of smaller increments of perhaps 10ms each, and to count the number of overflows for the required delay period. If you have a number of different intervals to generate, and maybe run concurrently, the second method would be the preferred one.

You would need to select the fixed frequency clock source to obtain a sufficiently long timing period, i.e. a frequency between the limits 15.625kHz and 19.531kHz, depending on the internal reference clock trim. This is the internal reference frequency divided by two. It is then a matter of setting the prescale value and the MTIMMOD value to obtain the required delay.

For example, a trim setting for a fixed frequency clock of 15.625kHz, a prescale setting of 64, and MTIMMOD = 170 would produce a delay in the vicinity of 700ms. The delay formula is PS*(MTIMMOD + 1) / FFCLK.

Regards,

Mac

Re: How make a delay?

PedroM — Wed, 22 Dec 2010 19:27:14 GMT

Hello,

Tkank very much, for quickily answers and for help. Until i can make one increments as code bellow? This correct?

if(SIP1_MTIM1){ //timer 20ms

q++;

if(q == 500){ //when it reaches x ms

LAMP = 1; //turn off lamp

q = 0;

}

else {

LAMP = 0;

}

(void) MTIM1SC_TOF;

MTIM1SC_TOF = 0;

Re: How make a delay?

bigmac — Thu, 29 Oct 2020 09:19:23 GMT

Hello Pedro,

I think that it would be a good idea for your delay processing to be generally applicable, and not specifically for the timing of a LED. To do this, I think that you would need two functions - one function to setup the delay in the first instance, and a second function that could be periodically polled to test for a delay timeout condition. Both these functions can then be called from your main loop to meet the requirements of your application.

// Global variable:unsigned int q;void set_delay( unsigned int x){   q = x;   MTIMSC = 0x20;  // Counter reset   MTIMSC_TOF = 0; // Clear flag}unsigned int test_timeout( void){   if (MTIMSC_TOF) {      MTIMSC_TOF = 0; // Clear flag
      if (q)  q--;   }   return q;
}

The following code snippet might be used to control the LED.

LAMP = 0;set_delay( 50);         // 1 second delaywhile (test_timeout()); // Wait for timeoutLAMP = 1;

If the COP (watchdog) is enabled, you will also need to clear the COP timer while you wait for timeout to occur.

Regards,

Mac