newb question

Bobb Fwed

I am very new to the propeller....eh, just got it this morning.
I am trying to start something simple, something I am familiar with...rctime ... I know there are other objects and whatnot that do the same thing, but I'm learning a new language, so I'd like to figure it out for myself.

I am using the DIP chips on the Propeller RPM.

Here is the code I have:

'' RCTIME test

CON

  pin  = 3

VAR

  long time1
  long timestack[noparse][[/noparse]6]                         ' stack space for rctime cog
  long dispstack[noparse][[/noparse]6]                         ' stack space for LED display cog

PUB Main

  coginit(1, RCTIME(@time1), @timestack)    ' start cog 1 on RCTIME
  coginit(2, Disp_no(@time1), @dispstack)   ' dislpay RCTIME results on cog 2
  repeat                                    ' do nothing for forever

PUB RCTIME(timeAddr) | time                 ' get RCTIME value
  repeat
    DIRA[noparse][[/noparse]pin]~~                             ' set as output
    OUTA[noparse][[/noparse]pin]~~                             ' set HIGH
    waitcnt(clkfreq / 1000 + cnt)           ' wait 1ms
    time := cnt                             ' store current count
    DIRA[noparse][[/noparse]pin]~                              ' set as input
     
    waitpeq(|< pin, |< pin, 0)              ' wait until low again ?I think? ... it seems to work like this
     
    long[noparse][[/noparse]timeAddr] := ((cnt - time) - 3300) / 2000 ' store time to global var and compensate for minimum time and variable size

PUB Disp_no(nfoAddr) | tmp                  ' display binary value to 10 segment LED on PRPM
  dira[noparse][[/noparse]16..25]~~                            ' set leds to output
  outa[noparse][[/noparse]16..25]~~                            ' set leds HIGH (turns off LED...why?)
  repeat                                    ' repeat forever
    tmp := long[noparse][[/noparse]nfoAddr] <# 1023            ' get global var and limit it to 1023 (10 bits)
    outa[noparse][[/noparse]16..25] := tmp                     ' on (show binary value)
    waitcnt(381 + cnt)                      ' wait minimum
    outa[noparse][[/noparse]16..25]~~                          ' off
    waitcnt(40000 + cnt)                    ' reduce these friggin' bright LEDS!

What I am trying to accomplish: one cog (cog 1) continuously reads the RCtime of a photoresistor I have, and the other cog (cog 2) continuously displays the value (at a reduced brightness).

What happens: as the RCtime increases the LEDs start to blink (as it seems it is waiting for the RCtime), and for some unexplainable reason, no matter what divider I put on the "store time to global var" line, it doesn't actually affect the output, which seems to mean, I am getting the value from somewhere else.

I would also like to add some type of max time allowed to wait for the pin to go low. But everything I did made the resolution of RCtime go way down.

Please help, and let me know of any errors I have in my code.

Post Edited (Bobb Fwed) : 6/25/2008 9:13:41 PM GMT

Mike Green

The stack sizes are way too small. Always use at least 20 longs at least.

The WAITCNT in Disp_no is too small for Spin. 381 + CNT will probably pass before the WAITCNT can execute. The minimum is more like 1100 if I remember correctly.

Bobb Fwed

The manual says 381 is minimum for the cnt operation--I actually discovered that first hand before I found it in the manual...look at page 323.

I can't use 20 longs, anything higher than 6 makes the LED segments stay on permanently, and below six makes them stay off. Someone tell me why. At 6 stacks it operates, just not exactly how I want.
I don't get the whole stack thing anyway...I thought each of these cogs have their own RAM...what do the stack accomplish?

Bobb Fwed

I take that back...with 10 or more on the stacks...it now works...I didn't have the right divider at the moment I posted last. So now it works, I am happy.
But someone explain the need for stacks?

Mike Green

The Spin interpreter needs some place to keep some basic information that's part of a method call. The main method of a Spin program and the methods in the COGINIT / COGNEW calls have to be called somehow and they use the same mechanism as a normal method call. All expressions and statements each use some amount of stack space for computation. Even just "A := 5" uses a location or two. More complicated expressions use more stack space. Local variables in a method including the parameters and the result all are allocated in the stack.

381 may be the "official" minimum, but I'd not count on it being adequate.

Bobb Fwed

Mike Green said...
381 may be the "official" minimum, but I'd not count on it being adequate.

Yeah, it's not a super important part of the program...just a part so I can see the value, not important timing stuff.

And thanks for the info...I'll keep in mind: "when in doubt, more stack space!"