Loops and microcontrollers

Question

This is what I am trying to figure out, I have a MC9S08AW60. It has two timers and I am trying to configure or just check for a tick from the timer, ie , I just want to check when the overflow flag changes. the basic design of the code is:

PTFDD = 0xFF;
int j,ch_nbr;
// LED mask values:
#define mLED0    0x01
#define mLED1    0x02
#define mLED2    0x04
#define mLED3    0x08
#define mLED4    0x10
#define mLED5    0x20
#define mLED6    0x40
#define mLED7    0x80



void main()
{

  While(j>0){

  ch_nbr++;
  if (ch_nbr == 8)  ch_nbr = 0;
  if (ch_nbr == 0)  PTFD = mLED0;  // Turn LED0 on, other LEDs off
  if (ch_nbr == 1)  PTFD = mLED1;  // Turn LED1 on, other LEDs off
  if (ch_nbr == 2)  PTFD = mLED2;  // Turn LED2 on, other LEDs off
  if (ch_nbr == 3)  PTFD = mLED3;  // Turn LED3 on, other LEDs off
  if (ch_nbr == 4)  PTFD = mLED4;  // Turn LED4 on, other LEDs off
  if (ch_nbr == 5)  PTFD = mLED5;  // Turn LED5 on, other LEDs off
  if (ch_nbr == 6)  PTFD = mLED6;  // Turn LED6 on, other LEDs off
  if (ch_nbr == 7)  PTFD = mLED7;  // Turn LED7 on, other LEDs off
  Mydelay();
   }
   } 
 void Mydelay(int *j)
{

 if (TPM1SC_TOF == 0) j=0;
 else j=1;
 return j;
 }

The idea is to check if the value "j" AND concurrently decide if the LED's should light up or not! This code doesnt work.Its been sometime since I used the C programming. I am a little shaky and need some help. A proper explanation would be nice. Please consider the following link for the Datasheet of the MCU: http://cache.freescale.com/files/microcontrollers/doc/data_sheet/MC9S08AW60.pdf

Can the Following function be replaced instead of the existing Mydelay:

int Mydelay(int& j)
{
 if(TPM1SC_TOF == 0) j=0;
 else j=1;
 return j;
}
void main()
{
  PTFDD = 0xFF;
int j,ch_nbr;
// LED mask values:
#define mLED0    0x01
#define mLED1    0x02
#define mLED2    0x04
#define mLED3    0x08
#define mLED4    0x10
#define mLED5    0x20
#define mLED6    0x40
#define mLED7    0x80   
  While(j==1)
 {
  ch_nbr++;
  if (ch_nbr == 8)  ch_nbr = 0;
  if (ch_nbr == 0)  PTFD = mLED0;  // Turn LED0 on, other LEDs off
  if (ch_nbr == 1)  PTFD = mLED1;  // Turn LED1 on, other LEDs off
  if (ch_nbr == 2)  PTFD = mLED2;  // Turn LED2 on, other LEDs off
  if (ch_nbr == 3)  PTFD = mLED3;  // Turn LED3 on, other LEDs off
  if (ch_nbr == 4)  PTFD = mLED4;  // Turn LED4 on, other LEDs off
  if (ch_nbr == 5)  PTFD = mLED5;  // Turn LED5 on, other LEDs off
  if (ch_nbr == 6)  PTFD = mLED6;  // Turn LED6 on, other LEDs off
  if (ch_nbr == 7)  PTFD = mLED7;  // Turn LED7 on, other LEDs off
 }
 Mydelay();
}

The first thing I notice is you've got 3 opening brackets and 5 closing brackets. — Foggzie, Dec 19 '12 at 18:28
Is this compiled? You call MyDelay without parameter. MyDelay function doesn't do any delay. Where j is defined? How LED_poll is called? You need to work with this question... — Alex F, Dec 19 '12 at 18:29
@AmigableClarkKant: the overflow flag is basically a Modulo counter ie a register which just counts upto 0xFF and then starts counting again from 0x00.At every switch the FLAG goes off!! — sheetansh, Dec 19 '12 at 18:34
@AlexFarber: it doesnt compile. it just marks the function with all the errors. — sheetansh, Dec 19 '12 at 18:36
Actually, I can't figure out what you are asking. Also, how is MyDelay() supposed to delay anything? Update your question with an explanation of what TPM1_TOF is for starters. And what does your current code do? Why doesn't it work? Does the LED light up always, or never? What are the symptoms? Generally, excellent questions here on Stackoverflow, receives excellent answers. — Prof. Falken, Dec 19 '12 at 18:44
Is TPM1_TOF a hardware counter which "overflows" to 0? If so, you need to busy wait with a while() loop on that, to make a delay around that. Also, if that is the case, how fast does it count? — Prof. Falken, Dec 19 '12 at 18:47

score 3 · Accepted Answer · edited May 23 '17 at 11:48

First of all, you might want to use bit shifting to simplify your code significantly (because that's what you are essentially doing, shifting a bit).

This means you don't need to have 8 constants for each position, but simply use the << operator to move the bit one position to the left on each iteration:

int MoveToLeft(int bitPosition)
{
    // shift left
    bitPosition = bitPosition << 1;

    // reset to '1' when we shift through all 8 bits
    if ((bitPosition & 0xFF) == 0)
        bitPosition = 1;

    return bitPosition;
}

Next, better way than polling the timer value is to use interrupt routines. You need to setup a function which will be invoked automatically whenever your timer finishes counting.

I am not sure if your code even works like this. Is your timer's purpose to create a delay between LED changes? Does your timer automatically resets itself? Something like this would be more logical if the timer only serves to wait before transition:

while (1) // repeat indefinitely
{
     // shift the bit
     ch_nbr = MoveLeft(ch_nbr);
     PTFD = ch_nbr;

     // while the timer is counting, do nothing
     while (TPM1_TOF == 0) 
     { }

     // reset the timer
     (not sure about this part, check your docs)
}

thank you for your perfectly stated reply. As for bit shifting i will keep that in mind. Yes, according to the datasheet, the timer resets itself. SO all i need to check for is when the flag goes ON/OFF when there is a switch between 0xFF to 0x00. if you take a look at the datasheet page 170, the TOF section. — sheetansh, Dec 20 '12 at 13:44

score 1 · Answer 2 · answered Dec 19 '12 at 18:32

1

Well if this is a cut-paste of your code you've got a few things to fix:

1st this line: While(j>0){ I don't see j declared or defined anywhere. The compiler should've generated an error on that, and While should be lowercase while ( j > 0 ).
Same with ch_nbr.
When you call MyDelay() you wrote it to take an &int and you probably meant (int *j), then you didn't pass it anything.
If needs to be lowercase if
And yes, as the comments showed you have 3 opening brackets { and 5 closing ones }.

Fix those, make sure it compiles now and then tackle any logic.

answered Dec 19 '12 at 18:32

Miles Alden

1,542
1
11
21

i have made the required changes! – sheetansh Dec 20 '12 at 14:14
Great! Is it working as expected now? Or are more changes needed? – Miles Alden Dec 21 '12 at 15:50

Fábio Perez · Answer 3 · 2012-12-19T18:40:10.580

You have more closing brackets than opening brackets. Try correcting this by matching brackets (indentation will help).
You didn't declare the variables j and cn_nbr anywhere, but you use them.
C statements are lowercase (while, not While).
You are calling Mydelay() without parameters, when Mydelay(int &j) expect a parameter. Also, &j returns the address of the variable j. I think you want int *j here. Read more about pointers.
Use switch or if ... else if instead of if ... if ... if .... Your code work both ways, but using switch or if else is faster.

Consider learning more about C programming here: http://www.cprogramming.com/

Loops and microcontrollers

3 Answers3