Measuring audio phase shift through a circuit with a PIC

[HankMcSpank]

H Paul,

Thank you very much for your input - truthfully, I was was getting too wrapped up in this over the weekend, but after drawing a blank with every avenue explored, I'm taking a self enforced mini break from that particular problem (I often find coming back to a project after a rest sparks new ideas & approaches). re your specific idea...I'll freely admit that I'm sort of out my depth when it comes to the inner working of interrupts (ie Picbasic interrupts vs ASM interrupts vs DT interrupts), but at one stage I do recall getting intensely intimate with the datasheet & having a "what the hell" pop at something *very* similar to what you mention - I saw no difference (but I will revisit in the light of your input)

I could really do with some interrupt big hitters to chime in & outline a little a bit about how to get such time sensitive interrupt timings down to the bare minimum (assuming your suggestion isn't the only attack) ....becuase as it stands right now, I have *NO* (zilch, nada, zero, scratch) idea why that comparator2 interrupt count will not register below 336 when I feed a very slightly phase lagged signal into comp2 ...and alas, the my future (parked) status as a multimillionaire who invented widget X depends on getting that count to reflect the time lag between comp1 & comp2 tripping


I'm in part slightly reticent to even push this one too much in the (highly possible) case there's something inherently wrong in my PIC /PICBasic approach - what I am convinced about is that the inputs to the comparators are without question correct - I may be pants at programming, but I know how to drive a scope, sig gen etc! (I think my youtube video illustrates the issue seems to be a valid one)

if anyone out their in the global 'PIC interest land' feels up to the challenge - they could see themselves what happens when they feed near identically phased signals (ie a clock?) into comparator1 & comparator2 (that said an identical signal might cause problems with a race scenario?...but I concede that most don't have the faciilities or interest to setup an all pass to phase shift the two signals!)...in principle, with identical (phase) signals into both comparators, the count for comparator 2 ought to be very close to zero (like single digits)

But I will come back to this (& first on the list will be your suggestion..if for no other reason thatn your is the only suggestion I have, lol) - I'm presently now working on Project Y - it's not gonna be the blockbuster that Widget X will be ...but got to keep keep my kids in Nike trainers somehow or other

Edit: While I'm publicily declaring my woeful lack of grasp of time sensitive h/w & corresponding code....I also wonder if changing my PIC might help to get that comp2 count down? (I'm using a 16F690 not becuase it's necessarily the most suitable - but it came bundled with my PIKIT2 starter kit & I've stuck with it from new and have started to get the hang of it a little - when your grappling in the dark as often as am, you need a torch that's familiar!), but I see a chart like this http://www.microchip.com/en_us/technology/xlp/ & then wonder, is there a more efficient PIC for doing this type of stuff out there...??? (eg pics optimised for single instructions - not even sure what that means but the bar chart looks like a shocker!)

[Jerson]

Hi Hank

Since you're stuck, I wonder if you could post/PM your code of now so that I can take a whack at it. I'll see if I can find your problem with the min value of comp2 value.

The barest minimum code which will compile and show the problem is sufficient. I should be able to run it.

Regards

[HankMcSpank]

Hi Hank

Since you're stuck, I wonder if you could post/PM your code of now so that I can take a whack at it. I'll see if I can find your problem with the min value of comp2 value.

The barest minimum code which will compile and show the problem is sufficient. I should be able to run it.

Regards

Many thanks Jerson.

The latest version of code was part of a hulking long program, but I found an earlier variant, which is purely deals with the comparator interrupt timer1 counting & therefore makes it a lot easier to look at...

@ __CONFIG _FCMEN_OFF & _HS_OSC & _WDT_OFF & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOR_OFF & _PWRTE_OFF

DEFINE  OSC 20          ' set Oscillator at 20Mhz.
DEFINE  NO_CLRWDT 1   ' PBP doesn't clear WDT automatically
DEFINE HSER_TXSTA 24h ' Enable transmit
DEFINE HSER_SPBRG 129 ' set USART to 9600 baud  @20Mhz

'*********************************************************************************
'16F690 Pin Connections....
' PIN# NAME     USE & CONNECTION
                '  1   Vdd      +5VDC power supply
TRISC.4 = 0     '  6   RC4      C2OUT
TRISC.3 = 1     '  7   RC3      C12IN3- (comparator1 input)
TRISC.2 = 1     '  14  RC2      C12IN2- (comparator2 input)
TRISA.2 = 0     '  17  RA2      C1OUT
                '  20  Vss      Ground
'*********************************************************************************
OSCCON.0 = %0001000 
txsta = %10100100   'setup the tx register
RCSTA.7 = 1         ' Enable RB7 for TX USART
INTCON.0 = 0        ' clears the RABIF Flag (to 0), COULD be 1 on reset (unique to F690)
ANSEL      = 0      'disable AtoD.
ANSELH     = 0      'disable AtoD.

'Turn on & Set up Comparator 1
CM1CON0.7 = 1       'Comparator 1 on.
CM1CON0.6 = 0       'C1OUT POLARITY BIT
CM1CON0.5 = 1       '1 = C1OUT is present on the C1OUT pin (pin 17)
CM1CON0.4 = 1       'C1OUT logic - 0 is not inverted  (1 for inverted)
CM1CON0.3 = 0       'unimplemented
CM1CON0.2 = 1       'Connect internally to the output of C1VREF   (or 0 for the the associated comp 'in' ext pin)
CM1CON0.1 = 1       'this bit with bit 1 set the external incoming pin - in this case c12in3- (pin 7)
CM1CON0.0 = 1       'this bit with bit 1 set the external incoming pin - in this case c12in3- (pin 7)

'Turn on & Set up Comparator 2
CM2CON0.7 = 1       'Comparator 2 on.
CM2CON0.6 = 0       'C1OUT POLARITY BIT
CM2CON0.5 = 1       '1 = C2OUT is present on the C2OUT pin (pin 6)
CM2CON0.4 = 1       'C1OUT logic is not inverted  (1 for inverted)
CM2CON0.3 = 0       'unimplemented
CM2CON0.2 = 1       'Connect internally to the output of C1VREF (or 0 for the the associated comp 'in' ext pin)
CM2CON0.1 = 1       'this bit with bit 1 set the external incoming pin - in this case c12in2- (pin 14)
CM2CON0.0 = 0       'this bit with bit 1 set the external incoming pin - in this case c12in2- (pin 14)

' Setup the internal VREF
VRCON.7 = 1         'Comparator1 CV Ref enable bit
VRCON.6 = 1         'Comparator2 CV Ref enable bit 
VRCON.5 = 0         'high or low range  0 = High Range, 1 = low range
VRCON.4 = 0         '0.6V Reference Enable bit   ....0 is disabled
VRCON.3 = 0         'these 4 bits set the divider of the VREF ladder 16 values - 7 should yield 1/2 VCC
VRCON.2 = 1         'these 4 bits set the divider of the VREF ladder 16 values - 7 should yield 1/2 VCC
VRCON.1 = 1         'these 4 bits set the divider of the VREF ladder 16 values - 7 should yield 1/2 VCC
VRCON.0 = 1         'these 4 bits set the divider of the VREF ladder 16 values - 7 should yield 1/2 VCC


Comp1Time       var  word    ' used to amalgamate TMR1 High & Low Bytes.
Comp2Time       var  word

      
INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System  PO90OOO9
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   CMP1_INT,  _Comp1_Int,   PBP,  yes
        INT_Handler   CMP2_INT,  _Comp2_Int,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

T1CON.0= 1  'start timer

Comp1Time = 0 'clear down Comp1Time, prior to starting.
comp2Time = 0  'clear down Comp2Time, prior to starting

@ INT_ENABLE  CMP1_INT     ; enable Comparator 1 interrupts
@ INT_ENABLE  CMP2_INT     ; enable Comparator 2 interrupts

'Main body of Code****************************************************************
Main:
        HSEROUT ["comp1=",dec Comp1Time,9,"comp2Time=", dec comp2time, 13, 10]
        PAUSE 80
        goto Main
        end       

'Comparator1 Interrupt Handler++++++++++++++++++++++++++++++++++++++++++++++++++++ 
Comp1_Int:
        Comp1Time.Lowbyte = TMR1L       'Store timer1 Low into a variable  
        Comp1Time.Highbyte = TMR1H      'Store timer1 high into a variable.
        TMR1H = 0                                   'Set the high part of the timer value to 0
        TMR1L = 0                                    'Set the low part of the timer value to 0

@ INT_RETURN


'Comparator2 Interrupt Handler++++++++++++++++++++++++++++++++++++++++++++++++++++ 
Comp2_Int:
        Comp2Time.Lowbyte = TMR1L       'Store timer1 Low into a variable 
        Comp2Time.Highbyte = TMR1H      'Store timer1 high into a variable.
        TMR1H = 0                                  'Set the high part of the timer value to 0
        TMR1L = 0                                   'Set the low part of the timer value to 0
        
@ INT_RETURN

[Jerson]

Hi Hank

I may be wrong here, but, my suspicion is you are losing time in reentering PBP in your ISRs. See, a lot of PBP registers have to be saved even if they are not going to be used because you flagged your ISR to be coded using PBP functions.

I suggest you slim it down by using ASM inside the ISR and avoiding ReEnterPbp. You should see better results.

I might sound like a heretic here, but I prefer coding my ISR in ASM even though it may be painful to code.

Regards

[Acetronics2]

Hi, Jerson

+ 1000 ...

when I see the interrupts content (!) I do not understand why not to write them in . asm ...

isn't worth saving and restoring all the PBP variables ... as saving and resetting TMR1 only need 4 more " _ " characters ...


Now ... thinking to it ...

if those measurements are " changed " while calculating frequency and Phase ...
not so good ... eh !

do not know about transmitting results nor ... ( didn't see any interrupt disabling around HSEROUT ...)

Alain

[HankMcSpank]

As a relative PIC (& programming) n00b, even I realised that with every interrupt (& there'll be a whole heap of them generated here), some registers need to be stored away to be picked up again once the interrupt has finished. As the incoming audio frequency rises, the interrupt rate gets higher & higher eg at 2.5Khz, that's an interrupt every 400us...but it's worse than that, becuause there are two comparators, so it's actually an interrupt every 200us!

So if having to store/restore registers every 200us, then it obviously makes sense to use the fastest interrupts - that's where I come unstuck ....I only presently know how to us DT's interrupts! (& I have no clue as to how fast they are vs ASM interrupts ...it's all a bit "Whoah...there goes scary stuff" at the moment!)

Re your comment...

I suggest you slim it down by using ASM inside the ISR and avoiding ReEnterPbp. You should see better results.

bearing in mind the actualy routine is quite small....

Comp1 Interrupt routine...
store timer 1 count to a Variable "X"
reset timer 1


Comp2 Interrupt routine...
store timer 1 count to a Variable "y"
reset timer 1

..... would it be possible to at least get me started?

Re the ISR - how would that be triggered?

Re the ISR content - what ASM would that entail?

I'm not expecting anyone to do this for me, but when you don't know where to even start....then any initial guidance is most welcome!

Edit: Also, are there any suitable tools that can help me work out what's going on inside the PIC - I'm thinking along the lines of simulating in step time (vs real time) & seeing what's going on wrt registers.

[cncmachineguy]

Comp1 Interrupt routine...
store timer 1 count to a Variable "X"
reset timer 1


Comp2 Interrupt routine...
store timer 1 count to a Variable "y"
reset timer 1

First I would combine these as Paul suggested. ASM provided in my above post.

..... would it be possible to at least get me started?

Of course! we will!

Re the ISR - how would that be triggered?

triggering is easy, just have to turn on PIE's and GIE.

Off the top of my head, there is some homework to be done. I am not sure how to share variables between ASM and PBP. I don't have my manual with me at work, but I do remember seeing it. Thats needs to be found. While you are reading it, see if says anything about needing to stack PBP stuff when entering ISR. Pic will take care of the important stuff, but what about bank select and such.

Re the ISR content - what ASM would that entail?

Thats the easy part

Edit: Also, are there any suitable tools that can help me work out what's going on inside the PIC - I'm thinking along the lines of simulating in step time (vs real time) & seeing what's going on wrt registers.

Do you use MPLAB? If so, I like the mplab sim in under debuggers. it's not real robust, but it will allow you to set things like the input pin, step through the program and watch reg's. I don't know if it works with PBP. Beyond that, hardware solutions start with something like ICD. and higher in the money scale.