Spin Language - Monitoring system clocks ticks

JoeFL

I'm fairly NEW to Spin, but picking it quite quickly. I know about the waitcnt() function where one
can wait a certain amount of time before program execution is continued.

I would like to be able to monitor the amount of system clock pulses/ticks since a certain event has happened without pausing program execution.

For instance, if an event has happened, not necessarily a Port event, I would like to be able to execute another event at a certain number of clock cycles since that event.

Say ... Time_Mark := cnt
Time_Mark_1/4sec := cnt + clkfreq/4
I'd like to be able to test whether Time_Mark_1/4sec has been reached.

Bobb Fwed

so something like this?

timespan := clkfreq >> 2 ' (clkfreq / 4 == quarter second)

  event_time := cnt ' mark when the event happened
  REPEAT UNTIL ((cnt - event_time) => timespan)
    '' do anything here, while waiting for enough cycles to pass
  ' timed event goes here

or

IF ((cnt - event_time) => timespan) ' just test at any point in your program
    ' timed event goes here

You can't do a simple "is-current-time-greater-than-target-time" because the clock only holds 32 bits, thus it rolls over, and it is signed, so you would get anomalous instantly true or always false problems.

ypapelis

Joe,

if you don't want to wait by using waitcnt, you can simply poll the value of cnt as it is by definition the counter of system clock pulses.

So to your code above, you can use : if ( cnt >= Time_Mark_1/4sec ) to detect if that time has been reached

JasonDorie

ypapelis: That may not always work, since longs are signed and the value may wrap around. For example, if the counter is 2,140,000,000 and you add 80 million to it, it rolls over past $7FFF_FFFF, which makes it a negative number. Comparing cnt to that value before the counter ALSO wraps around will incorrectly pass your test. Bob's version will work in either case.

kuroneko

There was a [thread=133065]similar thread[/thread] recently about the same problem in PASM. Apart from the fact that SPIN uses signed arithmetic (which would confine you to about 26sec @80MHz) this approach may be easier.

PUB null | goal

  ctra := constant(%0_11111_000 << 23)                  ' LOGIC always counter
  frqa := 1                                             ' increment at same rate as cnt

' Say ... Time_Mark := cnt
' Time_Mark_1/4sec := cnt + clkfreq/4
' I'd like to be able to test whether Time_Mark_1/4sec has been reached

  goal := clkfreq/4                                     ' 1/4sec
  [COLOR="red"]phsa := 0                                             ' reset timer[/COLOR]

  ' do stuff

  if phsa > goal
    ' we spent more than 1/4 of a second
  else
    ' we still have some time left

The important bit here is to reset the timer occasionally, otherwise you get into (signed) trouble.