(SOLVED) #USE_TIMER... get_ticks()

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

I am using a PIC18F67J60 with the following directives...

#use delay(crystal=25MHz,restart_wdt)
#use timer(tick=100us,bits=32,NOISR)

The compiler does not generate a warning with regard to tick timing, however, timing appears to be wrong by an approximate factor of 2... I have no idea why... Any help/suggestions would be appreciated...

asmallri · Joined: 12 Aug 2004 Posts: 1630 Location: Perth, Australia

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

So I think the #use delay 25Mhz is correct because the baud rate for my serial ports is scaled correctly...

You were right about the compiler warnings... But the problem is still not solved...

When I set, #use timer(tick=1ms,bits=32,NOISR) timing is now wrong by a factor of 20, instead of a factor of 2.

It would appear that the TICKS_PER_SECOND constant which is generated by the compiler is incorrect...

I subsequently tried, #use timer(tick=1ms,bits=32, define=tickPerSecond,NOISR)... I thought that perhaps the TICKS_PER_SECOND was being overwritten by the Ethernet Stack Ticks... Anyway the results of this were even more confusing.... get_ticks()/ticksPerSecond resulted in a count that appeared to increment at a rate of 10's of thousands per second.

Long story short, I'm stumped.

Ttelmah · Joined: 11 Mar 2010 Posts: 19260

First thing is read what things say!... Smile

Look at the manual for #use timer.
You are using it without a timer number, so it says the default is timer1.

Then look at the include file header for the Ethernet. You will find it tells you what timers the Ethernet requires/uses. Result 'of course' it is not going to work.

No warning, since the Ethernet code, just sets the timers up assuming them to be unused. The #use timer call has already setup timer1, but the later code does not know this has been done.....

Since you are using a PIC that has other timers, just tell #use timer, to use another. Timer3 typically, since this has similar features to timer1.

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

Ok I will try that, however, I did search the Ethernet Stack for timers.... TICK.C is the only module using timers and compilation is conditional. TMR1 is not used with PIC18 devices... See below...

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

Ok, I tried:

#use timer(timer=3,tick=1ms,bits=32, NOISR)

It makes no difference which timer I choose, the behavior is exactly the same... The compiler does not appear to be assigning the correct value to TICKS_PER_SECOND

Even more confusing is that if you define the ticks per second name in the use timer declaration the result becomes even more bizarre...

Pertaining to USE TIMER, The manual says:
"DEFINE=id --- Creates a define named id which specifies the number of ticks that will occur in one second. Default define name if not specified is TICKS_PER_SECOND. Define name must start with an ASCII letter 'A' to 'Z', an ASCII letter 'a' to 'z' or an ASCII underscore ('_')."

So wondering whether TICKS_PER_SECOND was being overwritten the Stack, I tried:

#use timer(timer=3,tick=1ms,bits=32, define=ticksPerSecond,NOISR)

Now instead of get_ticks()/TICKS_PER_SECOND resulting in a count that took 20 seconds to increment, get_ticks()/ticksPerSecond returns a number that is inordinately huge and increments at an inordinately rapid rate(~500,000,000 counts per second)...

So no closer to a solution...[/i]

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

Ok, I am now convinced that the compiler is broken...

TICKS_PER_SECOND is always 24414 regardless of the tick timer setting...

jeremiah · Joined: 20 Jul 2010 Posts: 1320

25MHz / 4 (standard PIC18 clock divider) / 256 (Timer clock divider) = 24,414.0625

This is at best 40.96us per tick. Try lowering your tick value to say 10us or 1us and see if TICKS_PER_SECOND changes

#use timer(timer=3,tick=10us,bits=32,NOISR)
#use timer(timer=3,tick=1us,bits=32,NOISR)

You might be hitting a hardware limitation based on the chip settings you provided.

uslimey · Joined: 27 Aug 2011 Posts: 22 Location: Baltimore, MD

TICKS_PER_SECOND is also defined by the Stack... The stack defines it as an integer, which overwrites the TICKS_PER_SECOND value derived from the CCS tick timer. This explains why the TICKS_PER_SECOND never changed.

Ok, so adding the DEFINE=TPS to the #USE TIMER directive told the CCS tick timer to use TPS instead of the default TICKS_PER_SECOND. This however, yielded even bigger errors, because unlike the Stack definition, the CCS compiler uses a float for the TICKS_PER_SECOND not an integer. The problem here is that the result of get_tick()/TPS is actually a float... Not a big deal unless you are trying to convert it to string using the %Lu formatter.

SO...
sprintf(retData, "%Lu",get_ticks()/TPS); // Format as Long Unsigned Int returned a massive number,

WHEREAS...
sprintf(retData, "%f",get_ticks()/TPS); //format as float returned sensible values.