Multiple signals on different pins at different times

Jkane

Hello,

I was wondering is there a way to send independent signals on pins, I was thinking I needed multiple cogs, set to start at a specific time, but I think there would be an issue of drift.

I have to send data on 8 pins, all have different signals on each pin, Is there a way to do this

regards

Jeff

Mike Green

It all depends on what the signals are and their relationships with each other (if any). If you end up needing to use multiple cogs, they can be "locked" into strict relationships with each other (and time) through the use of the system clock (CNT) and the WAITCNT instruction. There are two counters in each cog and they can produce different signals with different timings with the cog managing both of them with precise relationships with the system clock.

You'll have to tell us more about what you're trying to do.

Jkane

I have attached a file of the signals, but It seems using multiple cogs I can control each individually.

so could you give me an example of two independent cogs toggling two different pins at a few microsecond difference (independent of each other, I was wondering how to sync them together.

regards

Jeff

tomcrawford

If you want to produce repetitive signals, with pulse width of 1 uSec or better, you might try this arbitrary pattern generator.

Ariba

You can synchronize two cogs by waiting for the same CNT value or by waiting for a pin change for example.

Here is an example code. The first cog toggles P0 in a Spin loop, the second cog waits for the pos-edge on P0 and toggles P1 with 4us delay for 4us. This cog is programmed with assembly, because Spin is not fast enough for us timings.

CON
  _clkmode  = xtal1 + pll16x
  _xinfreq  = 5_000_000

PUB Main : tm
  DIRA[0] := 1
  cognew(@asmcog,0)
  tm := CNT
  repeat
    waitcnt(tm += 80_000)       'toggle P0 every ms
    OUTA[0] ^= 1


DAT
asmcog  mov      dira,p1
loop    waitpeq  p0,p0          'wait until P0 goes high
        mov      t1,CNT
        add      t1,#320
        waitcnt  t1,#320        'delay 4us
        or       outa,p1        'P1 high
        waitcnt  t1,#0          'delay 4us
        andn     outa,p1        'P1 low
        waitpne  p0,p0          'wait until P0 goes low
        jmp      #loop

p0      long    1
p1      long    1<<1
t1      res     1

'P0 _____--------_______------ cog0
'P1 ______-______________-____ cog1

Andy

Jkane

Ariba,

I would like them to be completely independent of each other, you mentioned that "waiting for the same CNT value" would be another way, vs watch each other, do you have an example of this, two cogs waiting for the a specific cnt timer value to begin transmission?

regards

Jeff

Mark_T

There's nothing magic about this, give each cog the same value to WAITCNT for. Make sure its far enough in
the future that it can't be missed by either cog (cog start up takes about 8192 clks, not counting any
code overhead). WAITCNT is global and precise to the clock.

Ariba

They can not be "completly independent" and synchronized at the same time.
One cog has to be the "Master" and tell the other one the CNT value to sync to.

Here is an example with two Spin cogs, they output a short pattern every 1ms started at the same time. After the syncpoint they are independent and can do different timings until the next syncpoint.

  _clkmode  = xtal1 + pll16x
  _xinfreq  = 5_000_000

VAR
  long  synctime                'global var for both cogs
  long  stack[20]

PUB Main : tm
  DIRA[0] := 1
  synctime := CNT + 40_000      'sync at now + 500us 
  cognew(secondcog,@stack)
  repeat
    waitcnt(synctime)           'wait for same synctime as other cog
    tm := CNT
    repeat 8
      waitcnt(tm += 4_000)      'toggle P0 every 50us 8 times
      OUTA[0] ^= 1
    synctime += 80_000          'next sync point 1ms later

PUB secondcog | tm2
  DIRA[1] := 1
  repeat
    waitcnt(synctime)           'wait for same synctime as other cog
    tm2 := CNT
    repeat 6
      waitcnt(tm2 += 6_000)     'toggle P1 every 75us 6 times
      OUTA[1] ^= 1

Andy