PBP projects for R/C models

[cncmachineguy]

ken, I think you should stick with the '887. You already have lots of experience with it and really it can suit your needs just fine.

If you want to jump up to the 18F, you may find yourself feeling like WOW, how do I do this. From what I have found, the 18F's just left me feeling like I had just stepped into a new world with regards to setting up and configuring it just to get it to run. You are doing basic stuff, ie no USB or 4 way PWM with encoder feedback. So the 887 can do that just fine.

BTW, I don't remember how fast you are running the PIC. Whats your osc speed?

[Kenjones1935]

My oscillator is 4Mhz (I think). I have done nothing to change it. Whatever it does naturally is what it is.

My guess is that SONAR triggering four times per second is sufficient.

Question: How do I create an interrupt every 1/4 second?

Ken

[mackrackit]

This is very helpful.
http://www.picbasic.co.uk/forum/cont....-PICMultiCalc

Probably the easiest way to get started is with ON INTERRUPT. It is not the most accurate, it will only interrupt when nothing else is going on. Sound silly but..
An example would be a long PAUSE, the ON INTERRUPT will flag and run when the PAUSE is finished. ASM interrupts or DT's instant interrupts will work as true interrupts, but for your case ON INTERRUPT should be close enough.

This should be close. Run it on your board and see what happens.

'FL PIC16F887
'16F887 INT RUPT
'44 PIN DEMO BOARD
   @ __config _CONFIG1, _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_OFF & _LVP_OFF & _CP_OFF
   INTCON.5 = 1
   OSCCON = %01110000 '8 Mhz
   DEFINE OSC 8
   OPTION_REG = %01000111  ' 1:256 PRESCALE
   ON INTERRUPT GOTO TLOOP
   CNT  VAR BYTE
   D    VAR BYTE
   D = 0
   DATA @10,10,20,30
   TCNT  VAR    BYTE
   
   START:
   FOR CNT = 0 TO 150
   PWM PORTD.7,D,10
   D = D + 2
   NEXT CNT
   GOTO START
   
   DISABLE
   TLOOP:
   TCNT = TCNT + 1
   INTCON.2=0
   IF TCNT = 8 THEN
   TOGGLE PORTD.4
   TCNT = 0
   ENDIF
   RESUME
   ENABLE

[cncmachineguy]

I agree walter, if going to the trouble, why not be correct.

Ken, heres something I was thinking,
Set up a 5msec interupt timer.
on each int, increment a counter
first count (@5msec) ping sonar 1
second count (@10msec) update servos
third count (@15msec) ping sonar 2
fourth count (@20msec) reset counter, write things (from looking at your code), adjust pulse times for next servo update.

so your int handler will do:
reload timer, inc counter, clear jump flags, retrun

main will do something like this:
if counter =1 and sonar1flag=0 then ping sonar 1
if counter =2 and update flag=0 then updateservos
if counter = 3 and sonar2flag=0 then ping sonar 2
if counter =4 and mathflag=0 then math stuff

in each subroutine first thing to do is set the flag, then do the routine.

[Kenjones1935]

cncmachineguy

Five millisec interrupts seems like a good plan. I will do a little more complicated counting and skipping. I think the SONARs should be less often if I am going to calculate velocity.

I wish I felt more at home with PBP. I'm tempted go to the freebe C, but that means starting all over again. It's been too many years.... Too lazy. sigh...

How do I get 5millisec interrupts from a FOSC/4 oscillator. I just do not understand section 6.0 of the '887 spec sheet.

Ken

[cncmachineguy]

cncmachineguy

Five millisec interrupts seems like a good plan. I will do a little more complicated counting and skipping. I think the SONARs should be less often if I am going to calculate velocity.

I'm not sure what needs to be more complicated, but I am prolly not seeing the whol picture. Velocity calc won't take long, I am sure it can still be done in the fourth block You have 5000 cycles to burn up before the next interupt.

I wish I felt more at home with PBP. I'm tempted go to the freebe C, but that means starting all over again. It's been too many years.... Too lazy. sigh...

I don't have any experience with PBP yet (but I will start programming in the next week or so ), all my programming has been in ASM. But from what I can see, there may be a few times when PBP isn't the best choice, but I don't know when that is. All languages have pros and cons. PBP seems to me to be a very good compilier. If I were you, I would just stick with it. I don't think it is where the difficulties are.

How do I get 5millisec interrupts from a FOSC/4 oscillator. I just do not understand section 6.0 of the '887 spec sheet.
Ken

For my part of being lazy, its not going to look at the datasheet for this processor. But the good news is I don't think I need to to answer this. I assume '887 has at least 1 16 bit timer you are not using. So go look at the timer section and figure out how to configure it as a counter. What I find to be the most important part about osc is this, it takes 4 clock cycles to execute an instruction (ASM). So that means if using 4Mhz clock, each instruction takes .000001 seconds, or 1/(osc/4). so for 5 msec, thats 5000 instructions. The timer/counter will increment 1 for every instruction. So heres the math:
16 bit counter = 65535
65535 - 5000 = 60535

so if you preload the timer with 60535, it will take 5000 counts to roll over. thats 5 msec. If timer overflow interupt is enabled, an int will be generated at 5 msec. Then in the handler, reload the timer with 60535 so another int will happen in 5 more msec. and so forth.

1 thing to keep in mind, 60535 assumes there is no lag between rollover and reload. In reality there is, it will take a few cycles to enter the interupt, then another few to reload and start the timer. so your number would adjust up by some small amount. for instance: if it takes 12 cycles to go from overflow to reload, the number you want to load would be 60535 + 12 = 60547. Make sense?

You can determine the exact number with some testing, before you reload the timer, grab the timer low byte and save it. then look at that number. it will be the number of cycles it took to get to the point where you grabbed it. Then replace the code to grab it with code to load it and the timing should be within 1 or 2 cycles.

I will let you chew on this for a while.
BTW, If you find there is not enough time between int for math and such, change the clock to 8Mhz, then you will be able to execute twice as many instructions between interupts.

[Kenjones1935]

There are plenty of machine cycles to do the math work and the control decisions. I think the 5 millisec interrupt timing should give me accurate timing for the PWM signals. I have no idea how much noise there is in the SONAR responses. I want to space them further apart in time so the trends are clear. Four triggers for each SONAR per second is my first guess.

Now to bed. Thanks.

Ken