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Groups > comp.arch.embedded > #20747

Re: Mecrisp on the TI Stellaris Launchpad

From rickman <gnuarm@gmail.com>
Newsgroups comp.arch.embedded, comp.lang.forth, comp.sys.raspberry-pi
Subject Re: Mecrisp on the TI Stellaris Launchpad
Date 2015-04-19 16:57 -0400
Organization A noiseless patient Spider
Message-ID <mh14qa$u9a$1@dont-email.me> (permalink)
References (6 earlier) <87h9sfwdy1.fsf@jester.gateway.pace.com> <mgrket$1d0$1@dont-email.me> <RRdYw.257010$Zf4.118346@fx22.am4> <mgrsbf$um9$2@dont-email.me> <2ivYw.272005$JH2.257361@fx11.am4>

Cross-posted to 3 groups.

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On 4/18/2015 12:06 PM, mm0fmf wrote:
> On 17/04/2015 22:02, rickman wrote:
>> I was commenting on the facts that there is a quarter volt lost across
>> the rPi
>
> It doesn't matter how much "is lost" because the final voltage is within
> spec.

You are confused.  The only reason why the output voltage is in spec is 
because the input voltage is well above the nominal voltage required on 
the input.  With another power module the output voltage would be 
outside of spec and even now, the output is not able to supply much 
current.  Connect a device that draws more current and the voltage sags 
more.

This is not so much about the USB spec as it is the design of the rPi 
which creates a lot of voltage drop on what should be very nearly a wire 
with nominal resistance.


> I don't know about the hub and PHY on the Pi, but all the PHYs we
> produce have the ability to disable VBUS on each port and can signal
> over current conditions. When a device pulls too much current you signal
> the USB MAC and it tells the PHY to kill VBUS. The missing volts will be
> loss in the PHY VBUS switch most likely.

Such a switch would typically have a resistance of low mOhms and create 
a correspondingly low voltage drop... much less than the 0.25 volts we 
are seeing in the rPi.


> I don't work with our PHYs directly but only with the USB MACs we
> produce so I can't recall off the top of my head if the over current is
> as programmable as the current the device claims during enumeration.
> Devices specify their max current requirements in multiples of 2mA
> units. Before enumeration, the spec allows 100mA and I'm fairly sure our
> PHYs will signal over current if something tries to draw much more than
> 100mA. Once enumerated, again I'm fairly sure the over current level is
> programmable.
>
>> and that the launchpad seems to reset when I type on the USB
>> keyboard.
>
> If the launchpad lies during enumeration then this can happen. It's not
> helped by the early Pi hardware being a bit more than flakey.

Bingo.


>>  Maybe it's not voltage related, but the quarter volt drop is
>> unexpected
>
> Not when you know there are switches between the power rail and VBUS as
> previously stated.

The rPi does not have switches in the power path I believe.  But if it 
does, they should be designed for a much lower voltage drop than a 
quarter volt, hence the problem.


>> and there are plenty of cases where even an older mouse, like
>> the one I have, can't be powered through the rPi.
>
> I have lots of devices that work perfectly with a Pi as long as they are
> connected before the Pi (model B, 512M) is booted. Plugging them in once
> booted normally results in a crash. Which is a shame as USB is designed
> to be hot-pluggable.
>
> I should really say that I am shocked, nay stunned to find that a £30
> single board PC which can be battery powered that runs Linux and
> provides a metric shit-load of IO in addition to Ethernet and USB has a
> number of gotchas and issues. ;-)

I find your description of the rPi to be interesting.  Battery powered 
is a bit tongue in cheek as this level device is on par with phones and 
tablets which can't be away from a power plug for hours rather than 
days.  I think of "battery powered" as describing equipment that can be 
left unattended for many days without an external power source.  But 
whatever, one man's battery is another man's RTG.  lol

Enjoy

-- 

Rick

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Thread

Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-02 21:08 -0400
  Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:18 -0700
    Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:25 -0700
      Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:33 -0700
        Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-13 21:45 -0400
          Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-13 21:47 -0400
            Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-14 07:33 -0700
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-14 14:38 -0400
    Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-16 14:24 -0700
      Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 15:11 -0700
        Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-16 23:37 -0400
          Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 20:59 -0700
            Re: Mecrisp on the TI Stellaris Launchpad Mel Wilson <mwilson@the-wire.com> - 2015-04-17 13:16 +0000
          Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 00:19 -0400
            Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 21:56 -0700
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 14:47 -0400
                WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-17 15:12 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Martin Gregorie <martin@address-in-sig.invalid> - 2015-04-17 20:14 +0000
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-17 16:59 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking David Brown <david.brown@hesbynett.no> - 2015-04-18 10:00 +0200
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-18 09:32 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Martin Gregorie <martin@address-in-sig.invalid> - 2015-04-18 15:15 +0000
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-18 11:31 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line   Breaking Niklas Holsti <niklas.holsti@tidorum.invalid> - 2015-04-18 19:21 +0300
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line   Breaking rickman <gnuarm@gmail.com> - 2015-04-19 16:39 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Alan Adams <alan@adamshome.org.uk> - 2015-04-18 18:52 +0100
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-18 18:55 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking The Natural Philosopher <tnp@invalid.invalid> - 2015-04-19 09:13 +0100
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-19 13:22 +0300
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking David Brown <david.brown@hesbynett.no> - 2015-04-19 22:09 +0200
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-17 21:15 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 17:02 -0400
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-18 17:06 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 16:57 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Alan Adams <alan@adamshome.org.uk> - 2015-04-20 09:33 +0100
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-20 18:03 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-21 01:16 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:20 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:24 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:40 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:57 -0700
                Re: Mecrisp on the TI Stellaris Launchpad Mel Wilson <mwilson@the-wire.com> - 2015-04-18 02:14 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 02:05 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:16 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 09:56 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:46 +0200
                USB serial ports, was: Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-04-18 18:34 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:04 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Jan Coombs <Jan-54 <jenfhaomndgfwutc@murmic.plus.com>> - 2015-04-18 09:38 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:54 +0200
                Re: Mecrisp on the TI Stellaris Launchpad hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) - 2015-04-18 15:36 -0500
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-04-23 07:59 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 14:35 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 15:44 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-08 12:00 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 03:36 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-05-10 10:32 +0100
                Re: Mecrisp on the TI Stellaris Launchpad Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-05-10 12:56 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 10:48 -0400
                Re: Mecrisp on the TI Stellaris Launchpad The Natural Philosopher <tnp@invalid.invalid> - 2015-05-10 16:05 +0100
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 23:26 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 09:37 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 11:16 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 23:42 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-11 02:17 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-05-10 11:41 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-05-10 16:56 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 13:01 -0400
                Re: Mecrisp on the TI Stellaris Launchpad lasselangwadtchristensen@gmail.com - 2015-04-18 12:13 -0700
            Re: Mecrisp on the TI Stellaris Launchpad stephen@mpeforth.com (Stephen Pelc) - 2015-04-18 19:22 +0000
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-04-20 13:24 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 13:23 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-22 20:44 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 13:51 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-22 19:10 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 15:31 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-23 02:08 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-24 02:52 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 14:40 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 15:42 -0400
                Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-21 09:34 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 14:57 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 15:35 -0400
          Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 10:52 +0000
            Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-17 14:05 +0300
            Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 07:56 -0700
              Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-17 17:26 +0200
              Re: Mecrisp on the TI Stellaris Launchpad glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-04-17 17:01 +0000
          Re: Mecrisp on the TI Stellaris Launchpad Blajrs Jrolrsen <boegre@no.com> - 2015-04-17 13:36 +0000
            Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-17 14:42 +0000
              Re: Mecrisp on the TI Stellaris Launchpad Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-04-18 00:25 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:03 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:14 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:26 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:32 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:47 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-18 08:47 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:19 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-18 15:52 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:07 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-06-09 03:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Robert Wessel <robertwessel2@yahoo.com> - 2015-04-18 00:11 -0500
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:32 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:26 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:57 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-18 09:42 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:11 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-04-18 12:19 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-18 15:16 +0300
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 19:57 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-18 23:11 +0300
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-19 21:32 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-19 23:04 +0300
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 09:15 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 12:17 +0200
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 13:08 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 20:17 +0200
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 15:33 +0000
            Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 14:52 -0400
            Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 20:06 +0000
      Re: Mecrisp on the TI Stellaris Launchpad lasselangwadtchristensen@gmail.com - 2015-04-16 16:18 -0700

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