CNT Confusion / Blinking LED Stalls

biznode

I must be forgetting something basic about CNT but I'm not seeing it.

Running on a PropBOE, I'd expect the following to blink the LED continuously.

Every minute or so it stalls on or off for about 10 seconds.

What am I missing?

Thanks.

-- Al



CON
_clkmode = xtal1 + pll16x '80MHz operating frequency.
_xinfreq = 5_000_000
LED_HEARTBEAT = 3

var
long HeartbeatCnt
long HeartbeatInterval



Pub Start
DIRA[LED_HEARTBEAT] := 1
OUTA[LED_HEARTBEAT] := 1
HeartbeatInterval := clkfreq / 1000 * 50
HeartbeatCnt := Cnt + HeartbeatInterval


repeat
if Cnt > HeartbeatCnt
OUTA[LED_HEARTBEAT] := ! OUTA[LED_HEARTBEAT]
HeartbeatCnt := HeartbeatCnt + HeartbeatInterval

Mike Green

CNT is a 32 bit unsigned number and > is a signed compare. You'll do better with

HeartbeatCnt := CNT
repeat
   if (CNT - HeartbeatCnt) > HeartbeatInterval
      !OUTA[LED_HEARTBEAT]
      HeartbeatCnt += HeartbeatInterval

pik33

cnt is going from $FFFFFFFF to $00000000 every 53 seconds

biznode

That was it.

Thanks for your help.

-- Al

JonnyMac

Here's another way to do that loop -- and you can do other things inside so long as the total timing doesn't take more than 50 ms

pub start | t

  dira[LED_HEARTBEAT] := 1 
  outa[LED_HEARTBEAT] := 1

  t := cnt
  repeat
    !outa[LED_HEARTBEAT]

    ' other code here

    waitcnt(t += (clkfreq / 20))