Re: UART connection between ATSAMD20 and ATtiny4313

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.arch.embedded
Subject	Re: UART connection between ATSAMD20 and ATtiny4313
Date	2023-04-27 09:17 +0200
Organization	A noiseless patient Spider
Message-ID	<u2d7ih$1qmgf$1@dont-email.me> (permalink)
References	<u2be3n$1a5nq$1@dont-email.me> <8c53b82a-f075-4b51-98bd-792221acbe60n@googlegroups.com> <u2c2eu$1hfgr$2@dont-email.me> <3400c428-350a-4826-adc8-df2c6105fc8bn@googlegroups.com>

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On 27/04/2023 02:10, Rick C wrote:

> I don't think the software UART is a lot of code, but you don't need
> that.  You need to write a routine to measure a bit time on the input
> to calibrate your clock to the incoming bit times.  That should not
> be a lot of code.  Translating a loop count into a bit clock setting
> for the UART should be a simple linear relationship, although it may
> involve a divide. You only need to work over a small range, so a
> small table lookup should be pretty close to optimal solution.
> 

That's definitely one way to do it, yes.

Have the master side send a couple of 0x00 bytes before the data, and 
use an interrupt on the Rx pin falling edge - when that comes in, count 
the time until a rising edge is seen.  If that time works out to within 
10% of the nominal expected time, you are calibrated and can turn off 
the interrupt.  Alternatively, send 0x55 bytes first and measure 
multiple short periods.  There will be some details to work out, 
depending on the what you are sending, the type of noise you expect, how 
often you need to re-calibrate, etc.  You are making a software 
equivalent to a PLL.

There's no need for a lookup table here (unless I've got my calculations 
upside down!).  The more cycles you count for the incoming trainer 
characters, the bigger the UART divider value you need.  That means your 
divisions will be done with constant values, and the compiler will turn 
those into multiplies.

An alternative is trial and error.  If your clock source is ±10%, and 
you need to get within ±2%, start your UART at the nominally correct 
baud rate.  If you don't receive error-free telegrams within a timeout, 
go 2% faster.  Keep adding 2%, stepping from +10% to -10%, until you hit 
a baud rate that works.

You can get even fancier here by figuring out the lowest and highest 
rates that work, then picking their average to get the best value.

Thread

UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-04-26 16:56 +0200
  Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-26 17:57 +0200
    Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-04-26 22:40 +0200
      Re: UART connection between ATSAMD20 and ATtiny4313 Grant Edwards <invalid@invalid.invalid> - 2023-04-26 21:00 +0000
        Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-26 17:20 -0700
        Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-04-27 10:15 +0200
  Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-26 09:26 -0700
    Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-04-26 22:44 +0200
      Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-26 17:10 -0700
        Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-27 09:17 +0200
        Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-04-27 10:28 +0200
          Re: UART connection between ATSAMD20 and ATtiny4313 Andrew Smallshaw <andrews@sdf.org> - 2023-04-27 13:28 +0000
            Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-27 09:22 -0700
              Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-28 09:48 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 01:55 -0700
            Re: UART connection between ATSAMD20 and ATtiny4313 Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-27 20:18 +0300
              Re: UART connection between ATSAMD20 and ATtiny4313 Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 23:03 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-28 09:58 +0300
              Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-27 17:45 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-28 10:00 +0300
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 00:21 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-28 11:43 +0300
                Re: UART connection between ATSAMD20 and ATtiny4313 Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 11:10 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-28 17:26 +0300
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 02:14 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 02:19 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-28 14:51 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 16:41 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-29 18:01 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-30 02:37 -0700
          Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-27 09:02 -0700
            Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-28 15:01 +0200
              Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-28 16:44 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-04-29 17:59 +0200
  Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-03 18:16 +0200
    Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-03 09:40 -0700
      Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-04 10:34 +0200
        Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-05-04 12:31 +0200
          Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-05 10:51 +0200
            Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-05-05 12:59 +0200
              Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-05 18:01 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Dimiter_Popoff <dp@tgi-sci.com> - 2023-05-05 19:52 +0300
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-07 23:20 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-05 11:37 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-07 23:21 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-05-08 08:37 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-08 09:24 +0200
            Re: UART connection between ATSAMD20 and ATtiny4313 Grant Edwards <invalid@invalid.invalid> - 2023-05-05 20:16 +0000
              Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-07 23:17 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-07 14:27 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 David Brown <david.brown@hesbynett.no> - 2023-05-08 08:34 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Dimiter_Popoff <dp@tgi-sci.com> - 2023-05-08 13:46 +0300
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-08 09:38 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Grant Edwards <invalid@invalid.invalid> - 2023-05-08 14:12 +0000
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-08 18:13 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-08 11:39 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-09 17:04 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-09 14:32 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-10 08:55 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Grant Edwards <invalid@invalid.invalid> - 2023-05-08 19:09 +0000
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-09 17:08 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-08 07:32 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-08 18:27 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-08 11:52 -0700
                Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-09 16:52 +0200
                Re: UART connection between ATSAMD20 and ATtiny4313 Grant Edwards <invalid@invalid.invalid> - 2023-05-09 15:10 +0000
                Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-09 14:29 -0700
        Re: UART connection between ATSAMD20 and ATtiny4313 Rick C <gnuarm.deletethisbit@gmail.com> - 2023-05-04 06:21 -0700
          Re: UART connection between ATSAMD20 and ATtiny4313 pozz <pozzugno@gmail.com> - 2023-05-05 11:02 +0200

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