Issues with timing on poll

Question

Issues with timing on poll

JesperNaarttijarvi opened this issue 2 years ago · comments

Jesper Naarttijärvi commented 2 years ago

We're trying to go away from a dependent rich library, pigpio-client to RPIO for our Wiegand readers but are facing some problems with the polls. Below is a snapshot of the current code and old code. Also, output from both codes. We seem to have a problem getting reads on low inputs. Both programs are running under the same circumstances and trying to read a card. What are we doing incorrectly?

Code is quite simple, we register two listeners, one for RX and one for TX, and listen to the callbacks.

EDIT: removed unnecessary code for readablility.
New code:

const rpio = require('rpio');
const start = new Date().getTime()

 wiegand.addWiegandListener = () => {
    wiegand.cbArgs.resetBinary = wiegand.resetBinary
    rpio.open(wiegand.tx, rpio.INPUT, rpio.PULL_UP);
    rpio.open(wiegand.rx, rpio.INPUT, rpio.PULL_UP);

    const cb = (pin) => {
      const level = rpio.read(pin)
      wiegand.wieCallback(pin, level)
    }

    rpio.poll(wiegand.tx, cb, rpio.POLL_LOW)
    rpio.poll(wiegand.rx, cb, rpio.POLL_LOW)
  }

  wiegand.watchPin = (pin, timeout) => {
    const localCb = () => {
      if (wiegand === undefined) {
        return
      }
      const level = rpio.read(pin)
      if (wiegand.level[pinNum] === level) {
        wiegand.wieCallback(pin, 3, null)
      }
    }
    let pinNum = 0
    if (pin === wiegand.rx) pinNum = 1

    if (wiegand.watching[pinNum]) {
      return
    }

    wiegand.watching[pinNum] = true
    wiegand.interval[pinNum] = setInterval(localCb, timeout);
  }

OLD CODE SNAPSHOT

  wiegand.addWiegandListener = () => {
    wiegand.cbArgs.resetBinary = wiegand.resetBinary

    const tx = wiegand.pigpio.gpio(wiegand.tx);
    const rx = wiegand.pigpio.gpio(wiegand.rx);

    tx.modeSet('input');
    rx.modeSet('input');

   // gpio.pullUpDown(pud, cb) pud=2: set pullup resistor, pud=1: set pulldown resistor, pud=0: clear resistor setting.
    tx.pullUpDown(2)
    rx.pullUpDown(2)

    tx.notify(wiegand.wieCallback.bind(null, wiegand.tx))
    rx.notify(wiegand.wieCallback.bind(null, wiegand.rx))
  }

  wiegand.watchPin = (pin, timeout) => {
    const localCallback = () => {
      if (wiegand === undefined) {
        return
      }
      gpio.read((_, level) => {
        if (wiegand.level[pinNum] === level) {
          wiegand.wieCallback(pin, 3, null)
        }
      })
    }
    let pinNum = 0
    if (pin === wiegand.rx) pinNum = 1

    if (wiegand.watching[pinNum]) {
      return
    }

    wiegand.watching[pinNum] = true

    const gpio = wiegand.pigpio.gpio(pin);

    wiegand.interval[pinNum] = setInterval(localCallback, timeout);
  }

COMMON CODE:

  wiegand.wieCallback = (pin, level, tick) => {
    if (wiegand === null) return
    console.group('wieCallback')
    console.log(`Pin: ${pin}, Level: ${level}`)
    console.log('TICK', tick)
    console.log('SINCE START', new Date().getTime() - start)
    console.groupEnd()

    let pinNum = 0
    if (pin === wiegand.rx) pinNum = 1

    wiegand.level[pinNum] = level

    //Accumulate bits until both gpios 0 and 1 timeout.

    // a falling edge indicates a new bit
    if (level === 0) {
      // First bit, start logging
      if (wiegand.inCode === undefined) {
        wiegand.bits = 1
        wiegand.num = 0

        wiegand.inCode = 1
        wiegand.watchPin(wiegand.tx, wiegand.pinTimeout)
        wiegand.watchPin(wiegand.rx, wiegand.pinTimeout)

      } else {
        wiegand.bits++
        wiegand.num <<= 1
      }

      if (pin === wiegand.tx) { // timeout gpio 14
        wiegand.txTimedout = false
      } else {
        wiegand.rxTimedout = false  // timeout gpio 15
        wiegand.num |= 1
      }

    } else if (level === 3) {
      if (wiegand.inCode !== undefined) {
        if (pin === wiegand.tx) { // timeout gpio 14
          wiegand.txTimedout = true
        } else {
          wiegand.rxTimedout = true // timeout gpio 15
        }

        if (wiegand.rxTimedout && wiegand.txTimedout) { // both gpios timed out
          wiegand.cbArgs.wiegand = wiegand
          if (wiegand.isFunction(wiegand.cb)) {
            wiegand.cb(wiegand.num, wiegand.bits, wiegand.cbArgs)
          }
        }
      }
    }
  }

  wiegand.addWiegandListener()

Output RPIO:

wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 39
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 41
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2140
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2142
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2146
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2148
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2149
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2151
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2152
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2154
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2155
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2156
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2157
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2159
wieCallback
Pin: 15, Level: 0
TICK undefined
SINCE START 2160
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2163
wieCallback
Pin: 15, Level: 0
TICK undefined
SINCE START 2164
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2166
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2167
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2168
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2170
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 2171
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 2174
wieCallback
Pin: 14, Level: 3
TICK null
SINCE START 2214
wieCallback
Pin: 15, Level: 3
TICK null
SINCE START 2217
checker [INFO] (0): new card: 3 | bits: 2
checker [INFO] (1): user not found for Card: 3
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5576
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5578
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5581
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5583
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5585
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5588
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5590
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5592
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5594
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5597
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5599
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5601
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5603
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 5606
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 5608
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9007
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9009
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9012
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9013
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9015
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9016
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9018
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9020
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9021
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9023
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9024
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9026
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9027
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9029
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9030
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9031
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9033
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9034
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9036
wieCallback
Pin: 14, Level: 0
TICK undefined
SINCE START 9037
wieCallback
Pin: 15, Level: 1
TICK undefined
SINCE START 9039
wieCallback
Pin: 14, Level: 1
TICK undefined
SINCE START 9041
wieCallback
Pin: 14, Level: 3
TICK null
SINCE START 9089
wieCallback
Pin: 15, Level: 3
TICK null
SINCE START 9091
checker [INFO] (2): new card: 0 | bits: 1
checker [INFO] (3): OK USER for Card: 0
reader [INFO] (0): Door was unlocked, leaving it.
*/

Output pigpio:
/*
wieCallback
Pin: 14, Level: 0
TICK 375151076
SINCE START 1574
wieCallback
Pin: 14, Level: 1
TICK 375151161
SINCE START 1579
wieCallback
Pin: 15, Level: 0
TICK 375152076
SINCE START 1582
wieCallback
Pin: 15, Level: 1
TICK 375152167
SINCE START 1584
wieCallback
Pin: 14, Level: 0
TICK 375153081
SINCE START 1587
wieCallback
Pin: 14, Level: 1
TICK 375153167
SINCE START 1591
wieCallback
Pin: 14, Level: 0
TICK 375154086
SINCE START 1592
wieCallback
Pin: 14, Level: 1
TICK 375154171
SINCE START 1593
wieCallback
Pin: 15, Level: 0
TICK 375155091
SINCE START 1595
wieCallback
Pin: 15, Level: 1
TICK 375155176
SINCE START 1596
wieCallback
Pin: 14, Level: 0
TICK 375156091
SINCE START 1597
wieCallback
Pin: 14, Level: 1
TICK 375156181
SINCE START 1598
wieCallback
Pin: 15, Level: 0
TICK 375157096
SINCE START 1601
wieCallback
Pin: 15, Level: 1
TICK 375157181
SINCE START 1602
wieCallback
Pin: 14, Level: 0
TICK 375158102
SINCE START 1603
wieCallback
Pin: 14, Level: 1
TICK 375158187
SINCE START 1604
wieCallback
Pin: 14, Level: 0
TICK 375159106
SINCE START 1605
wieCallback
Pin: 14, Level: 1
TICK 375159191
SINCE START 1606
wieCallback
Pin: 14, Level: 0
TICK 375160107
SINCE START 1607
wieCallback
Pin: 14, Level: 1
TICK 375160197
SINCE START 1608
wieCallback
Pin: 14, Level: 0
TICK 375161111
SINCE START 1610
wieCallback
Pin: 14, Level: 1
TICK 375161196
SINCE START 1612
wieCallback
Pin: 15, Level: 0
TICK 375162116
SINCE START 1613
wieCallback
Pin: 15, Level: 1
TICK 375162201
SINCE START 1614
wieCallback
Pin: 14, Level: 0
TICK 375163122
SINCE START 1620
wieCallback
Pin: 14, Level: 1
TICK 375163202
SINCE START 1621
wieCallback
Pin: 15, Level: 0
TICK 375164121
SINCE START 1622
wieCallback
Pin: 15, Level: 1
TICK 375164206
SINCE START 1623
wieCallback
Pin: 15, Level: 0
TICK 375165127
SINCE START 1624
wieCallback
Pin: 15, Level: 1
TICK 375165212
SINCE START 1625
wieCallback
Pin: 15, Level: 0
TICK 375166131
SINCE START 1626
wieCallback
Pin: 15, Level: 1
TICK 375166216
SINCE START 1627
wieCallback
Pin: 14, Level: 0
TICK 375167136
SINCE START 1629
wieCallback
Pin: 14, Level: 1
TICK 375167221
SINCE START 1630
wieCallback
Pin: 14, Level: 0
TICK 375168137
SINCE START 1631
wieCallback
Pin: 14, Level: 1
TICK 375168222
SINCE START 1632
wieCallback
Pin: 14, Level: 0
TICK 375169141
SINCE START 1634
wieCallback
Pin: 14, Level: 1
TICK 375169226
SINCE START 1635
wieCallback
Pin: 15, Level: 0
TICK 375170146
SINCE START 1636
wieCallback
Pin: 15, Level: 1
TICK 375170232
SINCE START 1637
wieCallback
Pin: 15, Level: 0
TICK 375171146
SINCE START 1644
wieCallback
Pin: 15, Level: 1
TICK 375171238
SINCE START 1645
wieCallback
Pin: 15, Level: 0
TICK 375172151
SINCE START 1646
wieCallback
Pin: 15, Level: 1
TICK 375172236
SINCE START 1646
wieCallback
Pin: 14, Level: 0
TICK 375173157
SINCE START 1647
wieCallback
Pin: 14, Level: 1
TICK 375173242
SINCE START 1648
wieCallback
Pin: 14, Level: 0
TICK 375174162
SINCE START 1648
wieCallback
Pin: 14, Level: 1
TICK 375174246
SINCE START 1649
wieCallback
Pin: 15, Level: 0
TICK 375175168
SINCE START 1650
wieCallback
Pin: 15, Level: 1
TICK 375175247
SINCE START 1650
wieCallback
Pin: 15, Level: 0
TICK 375176167
SINCE START 1651
wieCallback
Pin: 15, Level: 1
TICK 375176251
SINCE START 1652
wieCallback
Pin: 14, Level: 0
TICK 375177172
SINCE START 1652
wieCallback
Pin: 14, Level: 1
TICK 375177256
SINCE START 1653
wieCallback
Pin: 15, Level: 0
TICK 375178177
SINCE START 1654
wieCallback
Pin: 15, Level: 1
TICK 375178262
SINCE START 1654
wieCallback
Pin: 15, Level: 0
TICK 375179176
SINCE START 1655
wieCallback
Pin: 15, Level: 1
TICK 375179261
SINCE START 1656
wieCallback
Pin: 15, Level: 0
TICK 375180181
SINCE START 1656
wieCallback
Pin: 15, Level: 1
TICK 375180266
SINCE START 1657
wieCallback
Pin: 14, Level: 0
TICK 375181186
SINCE START 1658
wieCallback
Pin: 14, Level: 1
TICK 375181271
SINCE START 1659
wieCallback
Pin: 14, Level: 0
TICK 375182191
SINCE START 1660
wieCallback
Pin: 14, Level: 1
TICK 375182276
SINCE START 1661
wieCallback
Pin: 14, Level: 3
TICK null
SINCE START 1665
wieCallback
Pin: 15, Level: 3
TICK null
SINCE START 1667
checker [INFO] (0): new card: 1243028700 | bits: 32
checker [INFO] (1): user not found for Card: 1243028700
wieCallback
Pin: 14, Level: 0
TICK 378584400
SINCE START 5004
wieCallback
Pin: 14, Level: 1
TICK 378584485
SINCE START 5007
wieCallback
Pin: 15, Level: 0
TICK 378585400
SINCE START 5010
wieCallback
Pin: 15, Level: 1
TICK 378585485
SINCE START 5012
wieCallback
Pin: 14, Level: 0
TICK 378586405
SINCE START 5013
wieCallback
Pin: 14, Level: 1
TICK 378586490
SINCE START 5015
wieCallback
Pin: 14, Level: 0
TICK 378587410
SINCE START 5017
wieCallback
Pin: 14, Level: 1
TICK 378587495
SINCE START 5018
wieCallback
Pin: 15, Level: 0
TICK 378588410
SINCE START 5020
wieCallback
Pin: 15, Level: 1
TICK 378588500
SINCE START 5021
wieCallback
Pin: 14, Level: 0
TICK 378589415
SINCE START 5023
wieCallback
Pin: 14, Level: 1
TICK 378589500
SINCE START 5024
wieCallback
Pin: 15, Level: 0
TICK 378590420
SINCE START 5026
wieCallback
Pin: 15, Level: 1
TICK 378590505
SINCE START 5027
wieCallback
Pin: 14, Level: 0
TICK 378591425
SINCE START 5030
wieCallback
Pin: 14, Level: 1
TICK 378591510
SINCE START 5031
wieCallback
Pin: 14, Level: 0
TICK 378592430
SINCE START 5033
wieCallback
Pin: 14, Level: 1
TICK 378592515
SINCE START 5034
wieCallback
Pin: 14, Level: 0
TICK 378593430
SINCE START 5035
wieCallback
Pin: 14, Level: 1
TICK 378593515
SINCE START 5037
wieCallback
Pin: 14, Level: 0
TICK 378594435
SINCE START 5038
wieCallback
Pin: 14, Level: 1
TICK 378594520
SINCE START 5039
wieCallback
Pin: 15, Level: 0
TICK 378595440
SINCE START 5041
wieCallback
Pin: 15, Level: 1
TICK 378595525
SINCE START 5042
wieCallback
Pin: 14, Level: 0
TICK 378596440
SINCE START 5043
wieCallback
Pin: 14, Level: 1
TICK 378596525
SINCE START 5045
wieCallback
Pin: 15, Level: 0
TICK 378597445
SINCE START 5046
wieCallback
Pin: 15, Level: 1
TICK 378597530
SINCE START 5047
wieCallback
Pin: 15, Level: 0
TICK 378598450
SINCE START 5049
wieCallback
Pin: 15, Level: 1
TICK 378598535
SINCE START 5050
wieCallback
Pin: 15, Level: 0
TICK 378599455
SINCE START 5051
wieCallback
Pin: 15, Level: 1
TICK 378599541
SINCE START 5053
wieCallback
Pin: 14, Level: 0
TICK 378600460
SINCE START 5054
wieCallback
Pin: 14, Level: 1
TICK 378600540
SINCE START 5055
wieCallback
Pin: 14, Level: 0
TICK 378601460
SINCE START 5057
wieCallback
Pin: 14, Level: 1
TICK 378601545
SINCE START 5058
wieCallback
Pin: 14, Level: 0
TICK 378602465
SINCE START 5059
wieCallback
Pin: 14, Level: 1
TICK 378602550
SINCE START 5061
wieCallback
Pin: 15, Level: 0
TICK 378603470
SINCE START 5062
wieCallback
Pin: 15, Level: 1
TICK 378603555
SINCE START 5063
wieCallback
Pin: 15, Level: 0
TICK 378604470
SINCE START 5065
wieCallback
Pin: 15, Level: 1
TICK 378604560
SINCE START 5066
wieCallback
Pin: 15, Level: 0
TICK 378605475
SINCE START 5067
wieCallback
Pin: 15, Level: 1
TICK 378605560
SINCE START 5069
wieCallback
Pin: 14, Level: 0
TICK 378606480
SINCE START 5072
wieCallback
Pin: 14, Level: 1
TICK 378606565
SINCE START 5074
wieCallback
Pin: 14, Level: 0
TICK 378607485
SINCE START 5075
wieCallback
Pin: 14, Level: 1
TICK 378607570
SINCE START 5076
wieCallback
Pin: 15, Level: 0
TICK 378608485
SINCE START 5078
wieCallback
Pin: 15, Level: 1
TICK 378608575
SINCE START 5079
wieCallback
Pin: 15, Level: 0
TICK 378609490
SINCE START 5080
wieCallback
Pin: 15, Level: 1
TICK 378609575
SINCE START 5082
wieCallback
Pin: 14, Level: 0
TICK 378610495
SINCE START 5083
wieCallback
Pin: 14, Level: 1
TICK 378610580
SINCE START 5084
wieCallback
Pin: 14, Level: 3
TICK null
SINCE START 5087
wieCallback
Pin: 15, Level: 0
TICK 378611500
SINCE START 5089
wieCallback
Pin: 15, Level: 1
TICK 378611585
SINCE START 5091
wieCallback
Pin: 15, Level: 0
TICK 378612500
SINCE START 5092
wieCallback
Pin: 15, Level: 1
TICK 378612590
SINCE START 5093
wieCallback
Pin: 15, Level: 0
TICK 378613505
SINCE START 5095
wieCallback
Pin: 15, Level: 1
TICK 378613590
SINCE START 5096
wieCallback
Pin: 14, Level: 0
TICK 378614510
SINCE START 5097
wieCallback
Pin: 14, Level: 1
TICK 378614597
SINCE START 5099
wieCallback
Pin: 14, Level: 0
TICK 378615510
SINCE START 5100
wieCallback
Pin: 14, Level: 1
TICK 378615600
SINCE START 5101
wieCallback
Pin: 15, Level: 3
TICK null
SINCE START 5104
wieCallback
Pin: 14, Level: 3
TICK null
SINCE START 5122
checker [INFO] (2): new card: 1243028700 | bits: 32
checker [INFO] (3): user not found for Card: 1243028700

*/

fishbone1 · Answer 1 · Thu Jun 06 2024 00:15:51 GMT+0800 (China Standard Time)

I also have issues implementing a receiver for Wiegand messages with this library.

I identified two problems:

1: Sometimes we receive too many bits. I don't know how this could happen at all. My assumption is that the library's C code clears the event flag too quickly after reading it in function gpio_event_poll

	if ((rval = bcm2835_gpio_eds_multi(mask))) {
		bcm2835_gpio_set_eds_multi(rval);
	}

So maybe the same event is read again. Or the the Wiegand interface's sent signal is somehow unstable and contains multiple falling edges.
For me, it makes more sense to clear the flag after my poll callback has been called.
I patched my version of node-rpio to call bcm2835_gpio_set_eds_multi after the callback calls:

function event_poll()
{
	var active = bindcall(binding.gpio_event_poll, event_mask);

	for (gpiopin in event_pins) {
		if (active & (1 << gpiopin)) {
			module.exports.emit('pin' + gpiopin);
		}
	}

        // Patch here:
	bindcall(binding.gpio_clear_poll_event_flag, active);
}

I had to export the C function in rpio.cc:

NAN_MODULE_INIT(setup)
{
    NAN_EXPORT(target, gpio_clear_poll_event_flag);
//...

NAN_METHOD(gpio_clear_poll_event_flag)
{
	ASSERT_ARGC1(IS_U32);

	uint32_t mask = FROM_U32(0);

	bcm2835_gpio_set_eds_multi(mask);
}

and recompile it:

npm install node-gyp
cd node_modules/rpio
../.bin/node-gyp rebuild
cd ../..

and the result is a huge improvement.

Problem 2 is that some bits are missing sometimes, but surprisingly it happens not that often as problem 1. The reason is probably that JS is too slow. If I see your time measurements, then the callbacks sometimes take more than 3ms. This means that two signals have been sent in the meantime.

JS is probably not a good environment for such tasks. An idea to fix this is to move the polling code completely to C (maybe in a separate thread) and call a JS callback from there.

fishbone1 · Answer 2 · Fri Jun 14 2024 16:50:31 GMT+0800 (China Standard Time)

I came to the conclusion that the node-rpio module and the bcm2835 C-library on which it's based, simply just don't fit for this case. You need a library / module that relies on GPIO interrupts. This module not only doesn't use interrupts, it requires you to disable them at all.

This article makes it even more clear.

I ported everything to C and have similar issues, even though it's much faster. You have to ensure exact timing in order not to miss bits or receive extra bits. I need 1ms delay between polling which leads to noticable increase of CPU load.