Re: UART behavior for CTS/RTS - Kinetis bugs?

From	Grant Edwards <invalid@invalid.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: UART behavior for CTS/RTS - Kinetis bugs?
Date	2016-10-28 14:23 +0000
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<nuvn1l$9dl$1@reader2.panix.com> (permalink)
References	<93dc2e49-2495-4149-8f09-305b9038f599@googlegroups.com> <i_6dnfD3zY2R6Y_FnZ2dnUU7-bWdnZ2d@giganews.com> <nuv1if$hmq$1@dont-email.me>

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On 2016-10-28, David Brown <david.brown@hesbynett.no> wrote:
>
>> I believe that the only reasonable thing to do would be to finish sending 
>> the character, then wait until CTS is asserted before sending.
>
> Yes, anything else would disrupt the low-level behaviour of the
> UART, which is designed to transfer in units of one character.  If
> the transmitter broke off in the middle of the character, a receiver
> would see the start of the character followed by high bits.

Which is an entirely valid character assuming no parity.  It has a 50%
chance of being a valid character with parity enabled.  Stopping the
transmitter in mid-character is simply 100% broken.

> I also think it is odd to see something using hardware flow control in
> modern devices.  Hardware flow control can be a real pain when you have
> buffers, FIFOs, DMA, etc.

Why?  If hardware flow control is implemented properly (which means
it's in HW), then it's completely transparent regardless of buffers,
FIFOs, DMA, etc.  Trying to implement hardware flow control in
software is usually futile.

> Flow control is usually handled at a higher protocol level now.
> Rather than using CTS/RTS, or XON/XOFF, you define it at a higher
> level such as replying to telegrams with NACK's.  Or you just note
> that since your UART is running at perhaps 115kbps or less, and your
> microcontrollers are running at 50 MHz or more, you don't need any
> kind of flow control - each side is ready all the time.

-- 
Grant Edwards               grant.b.edwards        Yow! Civilization is fun!
                                  at               Anyway, it keeps me busy!!
                              gmail.com

Thread

UART behavior for CTS/RTS - Kinetis bugs? Dave Nadler <drn@nadler.com> - 2016-10-27 13:21 -0700
  Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-27 13:41 -0700
    Re: UART behavior for CTS/RTS - Kinetis bugs? Dave Nadler <drn@nadler.com> - 2016-10-28 10:42 -0700
      Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-28 11:15 -0700
        Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-28 11:21 -0700
        Re: UART behavior for CTS/RTS - Kinetis bugs? antispam@math.uni.wroc.pl - 2016-10-29 00:17 +0000
          Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-28 19:28 -0700
            Re: UART behavior for CTS/RTS - Kinetis bugs? upsidedown@downunder.com - 2016-10-29 13:57 +0300
      Seriial ports on PCs. (was Re: UART behavior for CTS/RTS - Kinetis bugs?) Paul <paul@pcserviceselectronics.co.uk> - 2016-10-29 09:03 +0100
        Re: Seriial ports on PCs. (was Re: UART behavior for CTS/RTS - Kinetis bugs?) upsidedown@downunder.com - 2016-10-29 14:12 +0300
          Re: Seriial ports on PCs. (was Re: UART behavior for CTS/RTS - Kinetis bugs?) Paul <paul@pcserviceselectronics.co.uk> - 2016-10-30 09:34 +0000
  Re: UART behavior for CTS/RTS - Kinetis bugs? Tim Wescott <seemywebsite@myfooter.really> - 2016-10-27 16:39 -0500
    Re: UART behavior for CTS/RTS - Kinetis bugs? Dimiter_Popoff <dp@tgi-sci.com> - 2016-10-28 01:02 +0300
    Re: UART behavior for CTS/RTS - Kinetis bugs? lasselangwadtchristensen@gmail.com - 2016-10-27 15:31 -0700
    Re: UART behavior for CTS/RTS - Kinetis bugs? David Brown <david.brown@hesbynett.no> - 2016-10-28 10:17 +0200
      Re: UART behavior for CTS/RTS - Kinetis bugs? Grant Edwards <invalid@invalid.invalid> - 2016-10-28 14:23 +0000
        Re: UART behavior for CTS/RTS - Kinetis bugs? David Brown <david.brown@hesbynett.no> - 2016-10-28 16:34 +0200
        Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-28 12:02 -0700
      Re: UART behavior for CTS/RTS - Kinetis bugs? Don Y <blockedofcourse@foo.invalid> - 2016-10-28 11:50 -0700
      Re: UART behavior for CTS/RTS - Kinetis bugs? upsidedown@downunder.com - 2016-10-29 01:51 +0300
        Re: UART behavior for CTS/RTS - Kinetis bugs? upsidedown@downunder.com - 2016-10-29 13:59 +0300
  Re: UART behavior for CTS/RTS - Kinetis bugs? Wolfgang Mahringer <yeti201@gmx.at> - 2016-10-28 16:45 +0200
  Re: UART behavior for CTS/RTS - Kinetis bugs? Hul Tytus <ht@panix.com> - 2016-10-28 22:28 +0000

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