Synchronized delay using timer0

[Jacques Nilo]

Hi all
I am trying to program synchronized delay using timer0 (timer1 being already used). I need usec precision. Something of the following structure:

Startwatch0 ' Initialization
some code here ' Execution time of this code can vary
do while (stopwatch0 < 1400 ) loop ' 1400 usec after startwatch0 the program continues

Any idea about the best way to proceed or any code example I could follow ?
Thank for your help !
Jacques

[kent_twt4]

I've never tried to get us precision with TMR0. This is a PIC device? If so, then I did try to get close by using On Interrupt Timer0Overflow, check for how many times, then wait for the remainder to pass in a Do While Loop. How the conditional statements are handled really depends on how much time the other code requires to run, if it is repetitive, and so forth.

To get us precision then would have to run it in a simulator like MPLAB or something else to account for all the overhead.

Untested pseudo code:

'Assuming 4 Mhz Clock then 1400us / 256 = 5 overflows, with 120us remainder
On Interrupt Timer0Overflow call CountOverflows '  
...
...
Main:
count = 0
clrf TMR0    'initialize TMR0 register to zero
...          'do code while waiting for timeout
...
Do Until count = 5    'waste whole number of overflows   
Loop
Do until TMR0.6 = 1   'waste remainder time till 120us is used up
Loop
Do until TMR0.5 = 1
Loop
'etc...
...    'do code after timeout
...
goto Main    'start over again

sub CountOverflows
    count += 1
    If count = 6 then count = 1
end sub

Edit: changed If statement count = 5, to Do Until count = 5 Loop

[Anonymous]

This is something I've been interested in, but haven't gotten around to yet. However I did notice that that free program I mentioned a while back has a utility in it for dealing with the overhead involved. It might prove useful.

http://sourceforge.net/p/gcbasic/discussion/629990/thread/4f502852/#08a7

[Jacques Nilo]

Hi tried kent_twt4 proposal. But apparently count does not increment itself. Here is my code. Any suggestion? Many thanks for your support !

;Chip Settings
#chip 16F690, 8

'Config UART
#define USART_BLOCKING true
#define USART_BAUD_RATE 19200
' Define serial port addresses
#define SerInPort  PORTB.5    ' RX
#define SerOutPort PORTB.7    ' TX
'Set pin directions
Dir SerInPort In
Dir SerOutPort Out
InitTimer1 osc,PS1_8

On Interrupt Timer0Overflow Call IncCounter

Sub IncCounter
    count += 1
    if count = 11 then count = 1 end if
End Sub

Function detect175Hz() as bit
' 140 sampling in 200ms
Repeat 140
  count = 0
  clrf TMR0
'  *** My code here ***
  Do Until count = 10 Loop    ' this should lead to 1400us after start ?
end repeat
end function

' Main program to test the lenght of detect175Hz 
clearTimer 1
StartTimer 1
detect175Hz
StopTimer 1
HSerPrint Timer1  ' should give back 50000 for 200ms sampling
hserprintCRLF

[kent_twt4]

Lots going on here, never hurts to simply code while checking basic functionality. Take a look at this line, it does not seem to make it thru to assembly code:

 Do Until count = 10 Loop

Should be:

Do Until count = 10
Loop

[Jacques Nilo]

I edited my previous post to keep it as short as possible... The line:
Do Until count = 10 Loop
did not generated any compiler error but I will try with what you sugest, do my homework, study MPLAB SIM and come back later on the forum with a solution or more questions :-)
Many thanks for your help. I appreciate.

[kent_twt4]

Can't possibly post up errors for every incorrect syntax? Here is the assembly for "Do Until count = 10 Loop. Condition is never met.

;Do Until count = 10 Loop    ' this should lead to 1400us after start ?
SysDoLoop_S1
;end repeat
    decfsz  SysRepeatTemp1,F
    goto    SysRepeatLoop1

Here is assembly for correct Do/Loop syntax.

;Do Until count = 10
SysDoLoop_S1
    movlw   10
    subwf   COUNT,W
    btfsc   STATUS, Z
    goto    SysDoLoop_E1
;Loop    ' this should lead to 1400us after start ?
    goto    SysDoLoop_S1
SysDoLoop_E1
;end repeat
    decfsz  SysRepeatTemp1,F
    goto    SysRepeatLoop1