Timer Problem with ATTiny85

[Philip Gansloser]

Hello,
I'm new to microcontroller programming, but try to learn constantly :-)
With the attached code I try to blink a LED on a ATTiny85 chip with 1 Hz frequency.
This works fine, but the intended fine tuning of the frequency by changing the SetTimer value (6) of Timer 1 shows no effect.
The blinking frequency always stays 1 Hz, even with a value of 255.

What am I doing wrong?

Kind regards
Philip

[Philip Gansloser]

Here is the code:

#chip tiny85, 16
#option Explicit
#define LED_1 PORTB.1

;--- Set unused pins to input + pullup to avoid drifting ports:
Dir PORTB IN       'set all pins to input
Set PORTB = 0xFF  'activate all internal pullups

Dir LED_1 OUT

Dim intervall as Byte
Dim warteseit, CounterValue_0, CounterValue_1, Pulse_Start, Pulse_Len as byte

Start:

'Enable portb.2 as the source of the interrupt. See the datasheet for more information.
'Trigger on change of PB2

On Interrupt Timer1Overflow Call IncCounter_1
IntOn   'enable Interrupts

;Timer1 prescaler  1/64 => with 16 MHz, 8bit counter overflows every 1024µs;
;with preload 6 overflow every 1000 µs
InitTimer1 Osc, PS_1_64
SetTimer 1, 6
StartTimer 1

intervall = 0
warteseit = 0

Set LED_1 On

Main:
  do forever


    ;Count Loops (0-10)
     intervall++
     if intervall = 50 then
       SET LED_1 Off
     end if

     if intervall >100 then
      intervall = 0
      Set LED_1 On
     End If

    ;Wait until next 10ms intervall starts
    do while (CounterValue_1 - warteSeit) <10
    ;emty loop
    loop
    warteseit+=10 ;next 10 ms Intervall

  loop

Sub IncCounter_1
        SetTimer 1, 6
        CounterValue_1 ++
End Sub

[Anobium]

Morning,

We need Boris. Boris Breuer bbreuer@users.sf.net

He is our expert on the Tiny85.

The timer code looks ok but the do while (CounterValue_1 - warteSeit) <10 loop is correct? Looks odd to me. CounterValue_1 has the range of 0 to 255 but warteseit will be the following sequence... 0, 10, 20, 30 .. 250, 4, 14, 24.... so, this test correct?

[Philip Gansloser]

Hi Anobium,

think I got it!
Instead of

SetTimer 1, 6 

now I use

TCNT1 = 6 ; 

Writing the value directly into the Timer1 register TCNT1 works fine.
Now it's possible to do a fine tuning of the time between the Interrup calls.

The "SetTimer" command seems not working on ATTiny85.

Thanks

[Anobium]

Must be an issue in the Settimer method.

Hopefully, one of the AVR guys can resolve for the future.

Well done in resolving

[Philip Gansloser]

Hi Anobium,

thanks for the reply.
The 'do while'-loop actually looks a bit weired, but it works fine.
Here is a short sequence of the values and the calculated results:

CounterValue_1	warteSeit	(CounterValue_1 - warteSeit)
	. . .
254	250	4
255	250	5
0	250	6
1	250	7
2	250	8
3	250	9
4	4	0
5	4	1
6	4	2
	. . .
12	4	8
13	4	9
14	14	0
15	14	1
16	14	2

[Frank Steinberg]

Hi,

I found out that the handling for the TCNT1 register for the subroutine SetTimer is missing in the timer library (timer.h). I added that in the attached "lcd.h" - line 1191 - #ifdef Var (TCNT1) ...
Please try it out.

Frank

[Anobium]

Let me know if this resolves the issue. And, I will copy to the release.

[Philip Gansloser]

Hello Frank,

thank you for your support and for providing the corrected timer library.
I will test it soon and report back then.

Philip

[Frank Steinberg]

I've tested with this:

; ----- Chip configuration:
#chip tiny85, 16.5

; ----- Include (software optimised) serial library:
#include <SoftSerial.h>

; ----- Config serial UART for sending:
#define SER1_BAUD 115200   ; 115200 baud
#define SER1_TXPORT PORTB  ; PortB.3 = Pin2 on AtTiny85
#define SER1_TXPIN 3       ;

; ----- Config Timer1:
InitTimer1 OSC, PS_1_32

; ----- Test Timer1 methods:

StartTimer 1      'start Timer1
Ser1Send  13      'new line in Terminal
Ser1Print Timer1  'send timervalue

ClearTimer 1      'set timervalue to zero
Ser1Send  13      'new line in Terminal
Ser1Print Timer1  'send timervalue

SetTimer 1, 100   'set timervalue to 100
Ser1Send  13      'new line in Terminal
Ser1Print Timer1  'send timervalue

StopTimer 1       'stop Timer1
SetTimer 1, 100   'set timervalue to 100
Ser1Send  13      'new line in Terminal
Ser1Print Timer1  'send timervalue

Terminal output is:
44
45
144
100

That's what to expect, so timer.h seems ok for me now. Please do another check anyway.

Frank

[Philip Gansloser]

Hello Frank,

i have also tested the new timer library in my project with success.
Works great!
Thanks again for your efforts.

Philip

[Anobium]

Thank you. I have updated the distribution.