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hemnath
Joined: 03 Oct 2012
Posts: 242
Location: chennai
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| internal timer wake-up problem |
 Posted: Wed Nov 07, 2012 5:26 am |
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Below program internal timer wake-up after 18 seconds.
Why it is so ?
After 18 seconds it start normally. why ?
| Code: | #include <18F2520.h>
#include <string.h>
#fuses INTRC_IO,NOWDT,NOLVP,PUT
#use delay(clock=31000)
#define EN PIN_A1
#define RS PIN_A2
#define INTS_PER_SECOND 15.1371 // (31000/(4*2*256))
INT16 seconds;
BYTE INT_count;
#INT_rtcc
void clock_isr()
{
if (--INT_count == 0)
{
++seconds;
INT_count = INTS_PER_SECOND;
}
}
void lcd_cmd(CHAR a); // function declaration
void lcd_print(CHAR rstr[]);
CHAR msg[16];
void main ()
{
set_timer0 (0) ;
setup_counters (RTCC_INTERNAL, RTCC_DIV_2|RTCC_8_BIT);
enable_interrupts (INT_RTCC) ;
enable_interrupts (GLOBAL) ;
output_low (RS);//set LCD to command mode
lcd_cmd (0x30);
lcd_cmd (0x01);
lcd_cmd (0x02);
lcd_cmd (0x0c);
lcd_cmd (0x06);
seconds =0;
WHILE (1)
{
output_low (RS);//set LCD to command mode
lcd_cmd (0x02);//move cursor to home position
sprintf (msg, "SECONDS %LU ", seconds ) ;
if (seconds==1)
{
output_high(pin_a3);
}
lcd_print (msg);
}
}
void lcd_cmd(CHAR a)
{
output_b (a);
delay_ms (10);
output_high (EN);
delay_ms (10);
output_low (EN);
}
void lcd_print(CHAR rstr[])
{
INT i;
FOR (i=0; rstr[i]!='\0'; i++)
{
output_high (rs);
lcd_cmd (rstr[i]);
}
}
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Ttelmah
Joined: 11 Mar 2010
Posts: 19466
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| Posted: Wed Nov 07, 2012 5:38 am |
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Well. The program never goes to sleep, so it doesn't "wake up after 18 seconds". Presumably you mean it starts updating the time?.
Remember, definitions like:
byte int_count;
does not initialise the variable. What it contains is random garbage that just happens to be in the RAM. So the actual count given, could be anything from 0 to 255....
byte int_count=INTS_PER_SECOND;
would initialise it.
Same applies to seconds, etc...
Best Wishes |
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hemnath
Joined: 03 Oct 2012
Posts: 242
Location: chennai
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| Posted: Wed Nov 07, 2012 6:15 am |
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When I power, it shows seconds in the display. After 18 seconds only, it displays the counts. eg: 0,1,2,3,4.......
Why it is waiting for 18 seconds to start the count ? Any problem with the code? |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Wed Nov 07, 2012 6:36 am |
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whats WRONG ??
hard to know where to start really.
beyond what Ttelmah noted:
| Quote: |
INT_count = INTS_PER_SECOND;
|
one of the above is an 8 bit integer - the other is def'd as a float.
and the assignment works , HOW??
and the supposed function of the int handler is what ?? |
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hemnath
Joined: 03 Oct 2012
Posts: 242
Location: chennai
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| Posted: Wed Nov 07, 2012 6:53 am |
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#define INTS_PER_SECOND 15
Now I have the changed it as integer.
Please check the example : EX_STWT.C |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19466
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| Posted: Wed Nov 07, 2012 9:09 am |
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| asmboy wrote: | whats WRONG ??
hard to know where to start really.
beyond what Ttelmah noted:
| Quote: |
INT_count = INTS_PER_SECOND;
|
one of the above is an 8 bit integer - the other is def'd as a float.
and the assignment works , HOW??
and the supposed function of the int handler is what ?? |
Won't matter C 'casts' values automatically. This works both ways.
Remember the #define doesn't actually generate any variable or anything, it is just a text substitution. However it is potentially confusing.
Other thing to think of is how slow the chip really is running. Just 7750 instructions per second. The boot sequence will easily be 100+ instructions, Then the LCD initialisation will take probably about 300mSec. The code in the printf, to actually generate the resulting value, could easily take a second of more to actually execute, so suddenly you are up to a couple of extra seconds before the first value displays. The delays from printf etc., will be there in every subsequent call, but will be constant, so the actual interval between the displays will be close to 'right', but the display could easily be a couple of seconds _after_ the number actually updated.
Best Wishes |
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andrewg
Joined: 17 Aug 2005
Posts: 316
Location: Perth, Western Australia
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| Posted: Thu Nov 08, 2012 12:53 am |
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Ttelmah answered this in his first reply. INT_count isn't initialised anywhere. Odds are, it starts at zero.
Next, INT_count is predecremented in clock_isr. Subtracting one from zero produces 255 for unsigned 8-bit integers. How long will that take to decrement back down to zero? 255 / 15 = 17 seconds!
Moral of the story: always initialise your variables before using them.
_________________
Andrew |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19466
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| Posted: Thu Nov 08, 2012 2:42 am |
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Yes, and if you add perhaps a second till the value actually displays (because of how slow the processor is), you are at 18+ seconds.
Best Wishes |
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hemnath
Joined: 03 Oct 2012
Posts: 242
Location: chennai
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| Posted: Thu Nov 08, 2012 3:31 am |
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Thank you so much  .. it's working now. |
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