Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.arch.embedded > #28134

Re: How do you read digital inputs from microswitch, jumpers, dip-switches...?

Show all headers | View raw

On 9/28/18 10:43 AM, Chris wrote:
> On 09/28/18 13:10, Richard Damon wrote:
> 
>>
>> My comment dealt with the fact that for many purposes, that 1-2 clock
>> tick delay is acceptable because it is 'fast' enough. In some
>> environments, like gaming, the delay may be unacceptable due to people
>> working on 'twitch' reflexes. For that sort of environment you need a
>> slightly more complicated coding which responds immediately to a switch
>> change, but then doesn't respond if the next sample falls back to the
>> old state, but delays that reaction for another sample (or two if cheap
>> bouncy switches). This gives immediate response without a risk of
>> bouncing. For this case sampling tends to be synchronous with the
>> display processing, which in some cases may be fast enough to otherwise
>> detect a bouncing switch. Avoiding a frame delay to denounce may be very
>> important as often you already have a frame delay from building frame
>> n+1 while frame n is being displayed to the user, so even instantaneous
>> reaction without a denounce delay can't affect the screen until frame
>> n+2. If it didn't happen until n+3, some gamers will notice (they are
>> actually probably somewhat anticipating), but 'frame perfect' is a thing
>> for some of them.
> 
> 
> Gaming might be a special case, but perhaps the way round
> that is to adjust the clock tick period to get the required
> response time ?. I doubt if 2 or 3 mS would be noticeable,
> but there are various other issues, such as how long a key
> must be down to be positively identified. A polling
> approach may not be good enough, depending on polling
> interval and or the system load elsewhere. For absolutely
> instant response, the only way is to add hardware to post
> an interrupt for any keypress, with the interrupt handler
> deciding what to do with it. Whatever solution, the
> keyprees has to get to the consumer process, either through
> polling ar perhaps a signal and task switch, so overall
> system architecture matters a lot and not later into the
> design when problems surface :-).
> 
> The reason I use such techniques is that a lot of the work
> done here is on none rtos platforms, often with inadequate
> hardware and running things like keyscanners in the
> background reduces complexity and allows more flexibility
> in the design of mainline code. Same applies to serial
> comms for example, where  an upper (mainline) and
> lower (interrupt) layer, with queues on tx and rx to connect
> the two, can offload a whole wedge of functionality...
> 
> Chris
> 

Raising the frequency can invalidate the debouncing. The key to
debouncing is that after the switch makes contact, it might rebound off
and bounce for a period of time. You thus need to do something to avoid
seeing the multiple on-off-on transitions. The period of this bouncing
is strongly a function of the type and quality of the switch, some (like
mercury wetted contacts) having inherently no bounce, while some cheap
leaf spring contacts can bounce for 10s of milliseconds.

Gaming is a bit special because time gets naturally quantized into
frames, everything happens in multiples of the frame (so 'polling' the
switch by reading it once a frame is natural, if a frame is longer than
the bounce period, you can ignore bouncing, if it is shorter you need to
do something to debounce (preferably without adding a frame delay). At
60 Hz, you are naturally sampling about every 16 ms, which is longer
than most bounce times, but controllers tend to get mashed a lot, so
sometimes you want to be a bit careful.

Back to comp.arch.embedded | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

How do you read digital inputs from microswitch, jumpers, dip-switches...? pozz <pozzugno@gmail.com> - 2018-09-20 11:52 +0200
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? John Speth <johnspeth@yahoo.com> - 2018-09-20 05:35 -0700
    Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? pozz <pozzugno@gmail.com> - 2018-09-21 09:42 +0200
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? David Brown <david.brown@hesbynett.no> - 2018-09-21 11:09 +0200
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 14:53 +0000
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-29 12:34 -0700
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Andrew Smallshaw <andrews@sdf.org> - 2018-09-21 09:16 +0000
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-21 06:22 -0700
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-21 10:04 -0500
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? lasselangwadtchristensen@gmail.com - 2018-09-21 14:47 -0700
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-22 21:57 -0500
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Andrew Smallshaw <andrews@sdf.org> - 2018-09-23 04:55 +0000
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-22 22:55 -0700
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-09-22 09:27 -0700
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 14:57 +0000
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Ed Prochak <edprochak@gmail.com> - 2018-10-05 09:52 -0700
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-10-05 14:40 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? gnuarm.deletethisbit@gmail.com - 2018-10-05 12:48 -0700
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Robert Wessel <robertwessel2@yahoo.com> - 2018-09-20 23:38 -0500
  Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-21 14:43 +0100
    Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Grant Edwards <invalid@invalid.invalid> - 2018-09-24 15:00 +0000
      Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-25 06:57 -0400
        Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-25 15:12 +0100
          Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 08:10 -0400
            Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2018-09-28 15:43 +0100
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 21:23 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Richard Damon <Richard@Damon-Family.org> - 2018-09-28 21:42 -0400
              Re: How do you read digital inputs from microswitch, jumpers, dip-switches...? Ed Prochak <edprochak@gmail.com> - 2018-10-05 10:04 -0700

csiph-web