Not confident with Interrupt.

[mkstevo]

I have always steered away from using interrupts, as I was never confident I knew what I was doing and found myself confused whenever I tried to read how to use them. As things are not too busy this week, I thought I'd have a look at trying to make sense of them. I am also experimenting with Chris Roper's millis() function. That section works very well, and I'm grateful to Chris for his excellent work and generousity in sharing it. I'm rather less confident in my work on the Interrupt, although it does seem to 'work'...

Here's my code:

'#Chip 16F874, 20 'This selects Crystal Oscillator of 20MHz
#Option explicit
#Config OSC = RC 'This selects RC Oscillator
#Chip 16F874, 4  '2k7 and 30pf on pin 13 just over 4MHz

#include "millis.h"       ' Include the Millis() Library

'Note:
'Pin 1 MUST connect to +5V to prevent being held in reset.

#Define     LED_Pin         PortA.0 'Pin2
#Define     LED_Pin2        PortA.1 'Pin3
#Define     LEDRate         1000    'Flash rate in mS
#Define     Int_Pin         PortB.4 'Pin37


'This includes an example of the use of the 'Millis() library
'millis() returns the number of milliseconds elapsed since the
'processor was powered up. It returns a Long variable value
'that will return to zero after 49 days of running. If checking
'for values being greater than millis() in programs intended to
'run for long periods, remember to watch for it resetting to zero.

Dim         CurMs           As Word
Dim         LstMs           As Word
Dim         Int_En          As Byte

Dir         LED_Pin         Out
Dir         LED_Pin2        Out

Dir         Int_Pin         In

'**********************************************************************
'Interrupt setup
'**********************************************************************
Let Int_En = INTCON       'Get Interrupt status

'INTCON.0        Change on PortB happened
'INTCON.1        External Interrupt on PortB
'INTCON.2        Timer0
'INTCON.3        PortB Change Enable
'INTCON.4        External Interrupt PortB Enable
'INTCON.5        Timer0 Enable
'INTCON.6        Peripheral Interrupt Enable
'INTCON.7        Global Interrupt Enable

Let Int_En.3 = 1 'Enable IOC for PortB
Let Int_En.0 = 0 'Clear any Interrupts

Let INTCON = Int_En       'Set Interrupt status

On Interrupt PortBChange Call Interrupt_Sub
'**********************************************************************
'Interrupt setup
'**********************************************************************

Let CurMs = 0
Let LstMs = 0

Do

    CurMs = millis()
    If CurMs - LstMs >= LEDRate Then    'Required Time has Elapsed
        Let LED_Pin = !LED_Pin          'So Toggle state of LED
        Let LstMs = CurMs               'And Record Toggle Time
    End If

    'This section tests to see if the IOC interrupts have been disabled.
    'They are turned off once we've responded to the button press.
    'We only want to re-enable them once the button has been released to
    'prevent multiple presses being recorded when only one has ocurred.

    If Int_En.3 = 0 Then                'IOC Interrupts are disabled
        Reset_Interrupt_Sub
    End If

Loop

Sub Interrupt_Sub
    Let Int_En    = INTCON              'Get Interrupt status
    If Int_En.0 = 1 Then
        If Int_Pin = 1 Then             'Button pressed
            Wait 10 mS
            If Int_Pin = 1 Then         'Still pressed
                Let LED_Pin2 = !LED_Pin2
                Let Int_En.0 = 0        'Reset the Interrupt On Change
                Let Int_En.3 = 0        'Stop the Interrupt On Change Service
            End If
        End If
    End If
    Let INTCON = Int_En
End Sub

Sub Reset_Interrupt_Sub
    If Int_Pin = 0 Then                 'Button released
        Wait 10 mS
        If Int_Pin = 0 Then             'Still released
            Let Int_En    = INTCON      'Get Interrupt status
            Let Int_En.3  = 1           'Enable IOC for PortB
            Let Int_En.0  = 0           'Clear any Interrupts
            Let INTCON    = Int_En      'Set Interrupt status
        End If
    End If
End Sub

As I said, this does work. If I press my button, I can toggle the state of the LED on Pin3 (PortA.1) whilst the LED on Pin2 (PortA.0) flashes under control of Chris's millis() function. If the button is held in, it is ignored until it has been released, and then presssed again. Super.

My lack of confidence is that the setup and implementation of the interrupt all seems a little 'messy'. I keep thinking that there should be a simpler way of doing this than the one I'm using.

I tried using one of the examples from the help pages that used this:

    'Setup the Interrupt
        Set IOCA.3 on
        Dir porta.3 in
        On Interrupt PORTABCHANGE Call Setir

I changed it to:

    'Setup the Interrupt
        Set IOCB.4 on
        Dir PortB.4 in
        On Interrupt PORTBCHANGE Call Interrupt_Sub

But this fails to compile, giving the error message "Error: Variable IOCB was not explicitly declared".

I just wondered if my approach could be improved?

[mkstevo]

I have managed to cobble something similar for the 16F1825, but again, it all seems rather untidy. The 16F1825 and 1829 seem to only have one external interrupt available (or I really misunderstood the datasheet) INTE, interrupt on edge. This requires two registers to be set, INTCON (bit 4) and the OPTION_REG (bit 6) which if set to 1 interrupts on a rising edge, if set to 0 interrupts on a falling edge. All of this assumes I did interpret the datasheet correctly, although it does seem to be working...

Any help would be most useful.

#Option explicit
#Chip 16F1825, 32

#Define OutPin     PortC.5 'Pin  5
#Define Int_Pin    PortA.2 'Pin  11

Dim     Int_En     As Byte

'Set pin directions
Dir OutPin          Out    'Pin  5


'**********************************************************************
'Interrupt setup
'**********************************************************************
Let Int_En = OPTION_REG   'Get Option status
Let Int_En.6 = 1 'Interrupt on rising edge
Let OPTION_REG = Int_En

Let Int_En = INTCON       'Get Interrupt status

'INTCON.0        Change on PortA happened
'INTCON.1        External Interrupt on PortA
'INTCON.2        Timer0
'INTCON.3        PortA Change Enable
'INTCON.4        External Interrupt PortA Enable
'INTCON.5        Timer0 Enable
'INTCON.6        Peripheral Interrupt Enable
'INTCON.7        Global Interrupt Enable

Let Int_En.4 = 1 'Enable INTE for PortA - Only Pin = Pin 11
Let Int_En.1 = 0 'Clear any Interrupts

Let INTCON = Int_En       'Set Interrupt status


On Interrupt ExtInt0 Call Interrupt_Sub
'**********************************************************************
'Interrupt setup
'**********************************************************************

Do

    'Do useful stuff here


    'This section tests to see if the INTE interrupts have been disabled.
    'They are turned off once we've responded to the button press.
    'We only want to re-enable them once the button has been released to
    'prevent multiple presses being recorded when only one has ocurred.


    If Int_En.4 = 0 Then                'INTE Interrupts are disabled
        Reset_Interrupt_Sub
    End If
Loop

Sub Interrupt_Sub

    Let Int_En    = INTCON              'Get Interrupt status

    If Int_En.1 = 1 Then
        If Int_Pin = 1 Then             'Button pressed
            Wait 10 mS
            If Int_Pin = 1 Then         'Still pressed
                Let OutPin = !OutPin
                Let Int_En.1 = 0        'Reset the Interrupt On Edge
                Let Int_En.4 = 0        'Stop the Interrupt On Edge Service
            End If
        End If
    End If
    Let INTCON = Int_En

End Sub

Sub Reset_Interrupt_Sub
    If Int_Pin = 0 Then                 'Button released
        Wait 10 mS
        If Int_Pin = 0 Then             'Still released
            Let Int_En    = INTCON      'Get Interrupt status
            Let Int_En.1 = 0            'Reset the Interrupt On Edge
            Let Int_En.4 = 1            'Start the Interrupt On Edge Service
            Let INTCON    = Int_En      'Set Interrupt status
        End If
    End If
End Sub

Thanks for looking.

[Anobium]

I think a little simplification of the code may help.

Can I just check? What exactly is the result you need?

[mkstevo]

What I'm initially aiming for is to familiarise myself with using interrupts triggered by an external source such as a switch.

At the moment everything I've designed and written the software for, continually polls the input(s) if a 'pulse' arrives, counts it once only, by waiting for the pulse to return to it's rest state then returns to updating the display, polling the input(s), sending serial data out if required and so on.

I was thinking that my software might be more elegant if I could use interrupts to monitor the input(s) which would count each pulse once only, whilst remaining vigilant for further potential pulses instead of hoping that any time taken updating the displays and whatever else didn't exceed the few mS of any pulse widths that might arrive at any time.

So something that allows me to catch a pulse width of between 10 mS - 500 mS without hogging the entire processor for the duration of that pulse, count each pulse once only and then be ready for another pulse almost immediately after the preceeding pulse finishes.

Which the above code does manage, if not very elegantly.

[Anobium]

The code is a lot easier. Look at the demos: C:\GCB@Syn\GreatCowBasic\Demos\vendor_boards\microchip_low_pin_count_demo_board\pickit2_board\16f1825\13_eeprom.gcb

This demo has a switch on a.3. Same chip also.

[mkstevo]

Thanks, I'll check that out next week.

I looked at the 'Help' but found it rather confusing. I never thought of looking at the examples after not finding much in the 'Help'.

I appreciate your reply and will report back once I've had another look.

[mkstevo]

Inspired by the example from the demos folder pointed out by Anobium, I have adjusted my program for the 16F1825. I couldn't get the Interrupt on Change example from the demos folder to work well for me. This seemed to fire the interrupt when the 'millis' function changed the LED state, and sometimes when the timer overflowed within the 'millis' function too. Whilst the interrupt still worked, the button needed to be pressed very firmly, and for at least 500mS. As I was hoping to capture short(ish) pulses in my final version this was a retrograde step.

I then looked at the example and wondered where the definitions for the interrupt constants were listed. I opened up the 16F1825.dat file and lo and behold, there they were.

Taking the defined constants as opposed to reading the entire contents of the INTCON register and the OPTION_REG regiter, setting the relevant bits and then writing them back to the PIC has tidied up the code by some measure. I also took the time to swap the interrupt from a rising to a falling edge to detect button presses and releases to ensure each button press is registered only once.

The changes have sped the detection of the button press then release quite significantly, keeping the button pressed and then held does not slow the operation of the program down either.

Whilst I'm not confident in using interrupts, I'm vastly less reluctant to use them now!

[mkstevo]

Here is the new and improved version:

'Uses 16F1825 and Millis_Zero

#Chip 16F1825, 32
#Option explicit
#Config CP=On

#Include "millis_zero.h"

'This includes an example of the use of the Millis() library
'millis() returns the number of milliseconds elapsed since the
'processor was powered up. It returns a Long variable value
'that will return to zero after 49 days of running. If checking
'for values being greater than millis() in programs intended to
'run for long periods, remember to watch for it resetting to zero.

'The version millis_zero.h starts from zero
'each time the processor is powered on.

#Define OutPin     PortC.5 'Pin  5
#Define Button     PortA.2 'Pin  11
#Define Beeper     PortC.3 'Pin  7

#Define LEDRate    1000 'mS


Dim         Count           As Byte
Dim         Pressed         As Bit

Dim         CurMs           As Word
Dim         LstMs           As Word

Dim         Cur_Millis      As Long
Dim         Int_Millis      As Long
Dim         Rel_Millis      As Long
Dim         Milli_Del       As Word

Dim         Reset_Trigger   As Bit
Dim         Trigger         As Bit


'Set pin directions
Dir OutPin      Out         'Pin  5
Dir Beeper      Out         'Pin  7
Dir Button      In          'Pin  11


Let CurMs         = 0
Let LstMs         = 0
Let Reset_Trigger = 0
Let Trigger       = 0
Let Count         = 0

Initialise
Test_Millis

Sub Test_Millis


    Do

        If Trigger = 1 Then
            Let Trigger = 0
            DoBip(1,25)  'Sound the buzzer
        End If

        If Reset_Trigger = 1 Then
            Let Reset_Trigger = 0
            DoBip(1,25)  'Sound the buzzer
        End If

        CurMs = millis()
        If CurMs - LstMs >= LEDRate Then    'Required Time has Elapsed
            Let OutPin = !OutPin            'So Toggle state of LED
            Let LstMs = CurMs               'And Record Toggle Time
        End If

    Loop

End Sub

Sub Initialise

    Do
        If Button = Pressed Then
            Let Pressed = !Button
            Let Count = 0
        End If
        Wait 5 mS
        Count++
    Loop Until Count > 125 'Get the idle state of the pin

    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

    'Interrupt flags

    'PS0,OPTION_REG,0
    'PS1,OPTION_REG,1
    'PS2,OPTION_REG,2
    'PSA,OPTION_REG,3
    'TMR0SE,OPTION_REG,4
    'T0SE,OPTION_REG,4 'Alias?
    'TMR0CS,OPTION_REG,5
    'T0CS,OPTION_REG,5 'Alias?
    'INTEDG,OPTION_REG,6
    'NOT_WPUEN,OPTION_REG,7

    'Option_Reg for rising/falling edge
    'INTEDG
    '
    'INTEDG = 1 'Rising Edge
    'INTEDG = 0 'Falling Edge

    Let INTEDG = Pressed      'Interrupt on switch pressed state

    'ExtInt0:INTE,INTF

    'IOCIF,INTCON,0
    'INTF,INTCON,1
    'TMR0IF,INTCON,2
    'IOCIE,INTCON,3
    'INTE,INTCON,4
    'TMR0IE,INTCON,5
    'PEIE,INTCON,6
    'GIE,INTCON,7
    'T0IF,INTCON,2
    'T0IE,INTCON,5

    'INTE = 1 'Interrupt on Edge enabled
    'INTE = 0 'Interrupt on Edge disabled

    'INTF = 1 'Edge Interrupt happened
    'INTF = 0 'No Edge Interrupt

    Let INTE   = 1 'Interrupt on Edge enabled
    Let INTF   = 0 'Clear any interrupts

    On Interrupt ExtInt0 Call Interrupt_Sub
    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

End Sub


Sub Interrupt_Sub

    If INTF = 1 Then
        If Button = Pressed Then             'Button pressed
            Wait 10 mS
            If Button = Pressed Then         'Still pressed
                Let Trigger  = 1
                Let INTEDG = !Pressed        'Change to interrupt on release
            End If
        End If
        If Button <> Pressed Then            'Button released
            Wait 10 mS
            If Button <> Pressed Then        'Still released
                Let Reset_Trigger = 1
                Let INTEDG = Pressed         'Change back to interrupt on press
            End If
        End If
    Let INTF   = 0 'Clear interrupt
    End If

End Sub

Sub DoBip(In NumberOfBips As Byte, LengthOfBips As Word)
    For Count = 1 To NumberOfBips
        SoundBeep(1) 'Beep on
        Wait LengthOfBips mS
        SoundBeep(0) 'Beep off
        Wait LengthOfBips mS
    Next
End Sub

Sub SoundBeep(In Sound As Bit)
    Let Beeper = Sound
    'Turn on or off the beeper
End Sub

[Anobium]

I removed all the code that was not needed show below.

A few points.
1. Not sure what millis_one.h is but I may be out of the loop with version of millis.h posted.
2. Let INTF = 0 'Clear interrupt. This may be needed initially but the interrupt service handler built in with Great Cow BASIC will clear INF for you. Try removing from your interrupt handler to verify the clear is happening (I can see it in the ASM but do check yourselve).

Looks very good! A demo in the making!!

'Basic
'Uses 16F1825 and Millis_Zero

#Chip 16F1825, 32
#Option explicit
#Config CP=On

#Include <millis.h>

'This includes an example of the use of the Millis() library
'millis() returns the number of milliseconds elapsed since the
'processor was powered up. It returns a Long variable value
'that will return to zero after 49 days of running. If checking
'for values being greater than millis() in programs intended to
'run for long periods, remember to watch for it resetting to zero.

'The version millis_zero.h starts from zero
'each time the processor is powered on.

#Define OutPin     PortC.5 'Pin  5
#Define Button     PortA.2 'Pin  11
#Define Beeper     PortC.3 'Pin  7

#Define LEDRate    1000 'mS


Dim         Count           As Byte
Dim         Pressed         As Bit

Dim         CurMs           As Word
Dim         LstMs           As Word

Dim         Cur_Millis      As Long
Dim         Int_Millis      As Long
Dim         Rel_Millis      As Long
Dim         Milli_Del       As Word

Dim         Reset_Trigger   As Bit
Dim         Trigger         As Bit


'Set pin directions
Dir OutPin      Out         'Pin  5
Dir Beeper      Out         'Pin  7
Dir Button      In          'Pin  11


Let CurMs         = 0
Let LstMs         = 0
Let Reset_Trigger = 0
Let Trigger       = 0
Let Count         = 0

Initialise
Test_Millis

Sub Test_Millis


    Do

        If Trigger = 1 Then
            Let Trigger = 0
            DoBip(1,25)  'Sound the buzzer
        End If

        If Reset_Trigger = 1 Then
            Let Reset_Trigger = 0
            DoBip(1,25)  'Sound the buzzer
        End If

        CurMs = millis()
        If CurMs - LstMs >= LEDRate Then    'Required Time has Elapsed
            Let OutPin = !OutPin            'So Toggle state of LED
            Let LstMs = CurMs               'And Record Toggle Time
        End If

    Loop

End Sub

Sub Initialise

    Do
        If Button = Pressed Then
            Let Pressed = !Button
            Let Count = 0
        End If
        Wait 5 mS
        Count++
    Loop Until Count > 125 'Get the idle state of the pin

    Let INTEDG = Pressed      'Interrupt on switch pressed state
    Let INTE   = 1 'Interrupt on Edge enabled
    Let INTF   = 0 'Clear any interrupts

    On Interrupt ExtInt0 Call Interrupt_Sub
    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

End Sub


Sub Interrupt_Sub

    If INTF = 1 Then
        If Button = Pressed Then             'Button pressed
            Wait 10 mS
            If Button = Pressed Then         'Still pressed
                Let Trigger  = 1
                Let INTEDG = !Pressed        'Change to interrupt on release
            End If
        End If
        If Button <> Pressed Then            'Button released
            Wait 10 mS
            If Button <> Pressed Then        'Still released
                Let Reset_Trigger = 1
                Let INTEDG = Pressed         'Change back to interrupt on press
            End If
        End If
    Let INTF   = 0 'Clear interrupt
    End If

End Sub

Sub DoBip(In NumberOfBips As Byte, LengthOfBips As Word)
    For Count = 1 To NumberOfBips
        SoundBeep(1) 'Beep on
        Wait LengthOfBips mS
        SoundBeep(0) 'Beep off
        Wait LengthOfBips mS
    Next
End Sub

Sub SoundBeep(In Sound As Bit)
    Let Beeper = Sound
    'Turn on or off the beeper
End Sub

[mkstevo]

Thanks for your suggestions.

I have removed the "Let INTF = 0 'Clear interrupt" statement as suggested. I hadn't realised the interrupt was cleared by GCB automatically. Is that cleared when exiting the interrupt handling sub routine?

I have also removed the references to 'Millis_Zero.h' and have re-incorporated the original 'millis.h'. I had been experimenting with setting the value returned by the millis() funtion to zero when the processor is first started. 'Millis_Zero.h' was a modified version of the original. I have moved the command that resets milis() to zero into my code, leaving the original unmodified.

[Anobium]

Yes, the Great Cow BASIC does clear the interrupt flags it handles. So, if INTE is enabled via the On Interrupt then the related INTF is cleared upon exit.

Good to read about the tidy up - when you are good and ready it would be very good to publish as a demonstration.

:-)

[mkstevo]

'**************************************************************************
'Enhanced 16F1825 version

'Uses 16F1825, millis and interrupts for a button.

'The interrupt triggers on a rising then falling edge to enable 
'counting of buttons only when a button is pressed and released.

'The button state is stored at startup to allow for buttons that
'may idle high or low automatically.

#Chip 16F1825, 32
#Option explicit
#Config CP=On

#Include "millis.h"

'This includes an example of the use of the 'Millis() library
'millis() returns the number of milliseconds elapsed since the
'processor was powered up. It returns a Long variable value
'that will return to zero after 49 days of running. If checking
'for values being greater than millis() in programs intended to
'run for long periods, remember to watch for it resetting to zero.

#Define OutPin     PortC.5 'Pin  5
#Define Button     PortA.2 'Pin  11
#Define Beeper     PortC.3 'Pin  7  'This connects directly to the positive connection
                                    'of  12V Piezo buzzer. The fact that a 12V buzzer
                                    'is driven from a 5V pin does not matter.
                                    'It is loud enough to hear!

#Define LEDRate    1000 'mS


Dim         Count           As Byte
Dim         Pressed         As Bit

Dim         CurMs           As Word
Dim         LstMs           As Word

Dim         Reset_Trigger   As Bit
Dim         Trigger         As Bit


'Set pin directions
Dir OutPin      Out         'Pin  5
Dir Beeper      Out         'Pin  7
Dir Button      In          'Pin  11


Let CurMs         = 0
Let LstMs         = 0
Let Reset_Trigger = 0
Let Trigger       = 0
Let Count         = 0

Initialise
Test_Millis

Sub Test_Millis

    Do

        If Trigger = 1 Then
            Let Trigger = 0
            DoBip(1,25)
        End If

        If Reset_Trigger = 1 Then
            Let Reset_Trigger = 0
            DoBip(1,25)
        End If

        CurMs = millis()
        If CurMs - LstMs >= LEDRate Then    'Required Time has Elapsed
            Let OutPin = !OutPin            'So Toggle state of LED
            Let LstMs = CurMs               'And Record Toggle Time
        End If

    Loop

End Sub

Sub Initialise

    Let MsCtr_ = 4294967295 'Set the value returned by the millis() function to it's
                            'maximum value. This effectively resets millis() to zero.
                            'If 'millis.h' cannot be found, this raises an error that
                            'a byte value cannot be set to 4294967295, that is why
                            'MsCtr_ is not set to 0 (zero) here.

    Do
        If Button = Pressed Then
            Let Pressed = !Button
            Let Count = 0
        End If
        Wait 5 mS
        Count++
    Loop Until Count > 125 'Get the idle state of the button pin

    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

    'Option_Reg for rising/falling edge
    'INTEDG

    'INTEDG = 1 'Rising Edge
    'INTEDG = 0 'Falling Edge

    Let INTEDG = Pressed      'Interrupt on switch pressed state

    'INTE = 1 'Interrupt on Edge enabled
    'INTE = 0 'Interrupt on Edge disabled

    'INTF = 1 'Edge Interrupt happened
    'INTF = 0 'No Edge Interrupt

    'INTE = 1 'Interrupt on Edge enabled
    'INTE = 0 'Interrupt on Edge disabled

    Let INTE   = 1 'Interrupt on Edge enabled
    Let INTF   = 0 'Clear any interrupts

    On Interrupt ExtInt0 Call Interrupt_Sub
    '**********************************************************************
    'Interrupt setup
    '**********************************************************************

End Sub

Sub Interrupt_Sub

    If INTF = 1 Then
        If Button = Pressed Then             'Button pressed
            Wait 10 mS
            If Button = Pressed Then         'Still pressed
                Let Trigger  = 1
                Let INTEDG = !Pressed         'Set the interrupt to trigger on release
            End If
        End If
        If Button <> Pressed Then             'Button released
            Wait 10 mS
            If Button <> Pressed Then         'Still released
                Let Reset_Trigger = 1
                Let INTEDG = Pressed            'Set the interrupt back to trigger on press
            End If
        End If
    End If

End Sub

Sub DoBip(In NumberOfBips As Byte, LengthOfBips As Word)
    For Count = 1 To NumberOfBips
        SoundBeep(1) 'Beep on
        Wait LengthOfBips mS
        SoundBeep(0) 'Beep off
        Wait LengthOfBips mS
    Next
End Sub

Sub SoundBeep(In Sound As Bit)
    Let Beeper = Sound
    'Turn on or off the beeper
End Sub