Protecting UART ports while SYSEN is low

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Protecting UART ports while SYSEN is low

ebtschi
Hello,

I have read this item in the board design requirements:

Use the SYSEN line to protect any IO pins to the OMAP CPU. SYSEN is
brought high when the Overo is ready to communicate; driving GPIOs
before this point can damage the processor.

Can this problem be avoided by simply adding a 330R series resistor on
the RX line of the Overo?

Best regards,
Ewald

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Re: Protecting UART ports while SYSEN is low

sturnfie
Ewald Kantner wrote
Hello,

I have read this item in the board design requirements:

Use the SYSEN line to protect any IO pins to the OMAP CPU. SYSEN is
brought high when the Overo is ready to communicate; driving GPIOs
before this point can damage the processor.

Can this problem be avoided by simply adding a 330R series resistor on
the RX line of the Overo?

Best regards,
Ewald
Hi Ewald,

Ahh yes that's a fun one. The issue seems to be with internal voltage domain biasing of the OMAP. If the GPIOs are not initialized and a voltage is present on the inputs, the internal voltage rails of the OMAP are driven higher than intended and bad things happen during initialization. I had a design that drove the UART1/3 lines immediately on power-on...one board lasted 2 months,  another lasted 7, and a couple more are still running (we're working on getting them returned for replacement with the new revision..)

Limiting the current with a series resistor certainly is better than leaving a direct line, but I'd suggest not driving the lines at all until the PMIC indicates that the system is ready (via the SYSEN line). I now use SYSEN to gate a voltage regulator on the low side of level shifters (I usually have to step voltages down to the Overo's +1.8V drive and this was a convenient way to get all the GPIO lines at once).

IIRC, I think Steve Sakoman was the guy who tracked down the issue. You might find more precise info on this forum somewhere in one of his posts..

Lucas
--
Lucas Sturnfield
sturnfie@gmail.com
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Re: Protecting UART ports while SYSEN is low

ebtschi
Hi Lucas,

thank you for your reply.

I also found this thread:
http://gumstix.8.n6.nabble.com/Overo-module-seems-dead-root-cause-td641684.html

One user also used series resistors to solve the problem. As far as I can see there is a pullup needed anyway, to avoid detecting a break condition on the UART line. Could this also be a problem? Moving from high-impedance to high at a time defined by SYSEN (or a little bit after that) seems a bit unsafe.
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Re: Protecting UART ports while SYSEN is low

araasch
Ewald:

Since what you most likely want is a reliable embedded computer
solution, I would avoid trying to use resistors to avoid this
potential problem.

TI recommends not driving the GPIO pins until allowed to do so as
indicated by SYSEN, so follow their advise.

To do otherwise puts your design in the "experimental" catagory, where
your system may experience lower MTBF, or erratic behavior.

This behavior could be dependant on minor changes in supply voltage or
on temperature.

If you only have to protect a couple GPIO lines you could use FETs to
provide the required isolation, otherwise look to gate a voltage
regulator as TI and others have indicated.

Thanks,

-Arlen



On Mon, Jan 9, 2012 at 5:12 AM, ebtschi
<[hidden email]> wrote:

> Hi Lucas,
>
> thank you for your reply.
>
> I also found this thread:
> http://gumstix.8.n6.nabble.com/Overo-module-seems-dead-root-cause-td641684.html
>
> One user also used series resistors to solve the problem. As far as I can
> see there is a pullup needed anyway, to avoid detecting a break condition on
> the UART line. Could this also be a problem? Moving from high-impedance to
> high at a time defined by SYSEN (or a little bit after that) seems a bit
> unsafe.
>
> --
> View this message in context: http://gumstix.8.n6.nabble.com/Protecting-UART-ports-while-SYSEN-is-low-tp3274358p3511548.html
> Sent from the Gumstix mailing list archive at Nabble.com.
>
> ------------------------------------------------------------------------------
> Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a complex
> infrastructure or vast IT resources to deliver seamless, secure access to
> virtual desktops. With this all-in-one solution, easily deploy virtual
> desktops for less than the cost of PCs and save 60% on VDI infrastructure
> costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox
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Re: Protecting UART ports while SYSEN is low

Keane, Ben (STRX)
In reply to this post by ebtschi
Is this protection only required for UART or for all GPIO pins?

> -----Original Message-----
> From: ebtschi [mailto:[hidden email]]
> Sent: Monday, 9 January 2012 8:13 PM
> To: [hidden email]
> Subject: Re: [Gumstix-users] Protecting UART ports while SYSEN is low
>
> Hi Lucas,
>
> thank you for your reply.
>
> I also found this thread:
> http://gumstix.8.n6.nabble.com/Overo-module-seems-dead-root-ca
> use-td641684.html
>
> One user also used series resistors to solve the problem. As
> far as I can see there is a pullup needed anyway, to avoid
> detecting a break condition on the UART line. Could this also
> be a problem? Moving from high-impedance to high at a time
> defined by SYSEN (or a little bit after that) seems a bit unsafe.
>
> --
> View this message in context:
> http://gumstix.8.n6.nabble.com/Protecting-UART-ports-while-SYS
> EN-is-low-tp3274358p3511548.html
> Sent from the Gumstix mailing list archive at Nabble.com.
>
> --------------------------------------------------------------
> ----------------
> Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't
> need a complex infrastructure or vast IT resources to deliver
> seamless, secure access to virtual desktops. With this
> all-in-one solution, easily deploy virtual desktops for less
> than the cost of PCs and save 60% on VDI infrastructure
> costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox
> _______________________________________________
> gumstix-users mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gumstix-users
>
> ______________________________________________________________________
> CAUTION: This message was sent via the Public Internet and
> its authenticity cannot be guaranteed.
>

PROPRIETARY: This e-mail contains proprietary information some or all of which may be legally privileged.  It is intended for the recipient only.  If an addressing or transmission error has misdirected this e-mail, please notify the authority by replying to this e-mail.  If you are not the intended recipient you must not use, disclose, distribute, copy, print, or rely on this e-mail.

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Re: Protecting UART ports while SYSEN is low

araasch
Ben:

The OMAP processor expects all I/O lines to be driven only after the
proper power up sequence has completed, and that all I/O lines to the
OMAP processor stop being driven before the proper power down sequence
begins.

If you choose to drive any I/O lines before the power up sequence has
started, or continue to do so while shutting power off to the
processor,  you are using the OMAP processor out of the manufacturer
recommendations, and TI does not define how the device will behave.

Thus, it is a good idea to not use the device in this way.

The TI TPS65950 Power Management IC provides the SYSEN signal that
goes high when it is allowable to start driving the I/O lines.

Use this signal to enable driving all I/O to the OMAP processor, and
you will be fine.

Thanks,

-Arlen

On Mon, Jan 9, 2012 at 6:01 PM, Keane, Ben (STRX) <[hidden email]> wrote:

> Is this protection only required for UART or for all GPIO pins?
>
>> -----Original Message-----
>> From: ebtschi [mailto:[hidden email]]
>> Sent: Monday, 9 January 2012 8:13 PM
>> To: [hidden email]
>> Subject: Re: [Gumstix-users] Protecting UART ports while SYSEN is low
>>
>> Hi Lucas,
>>
>> thank you for your reply.
>>
>> I also found this thread:
>> http://gumstix.8.n6.nabble.com/Overo-module-seems-dead-root-ca
>> use-td641684.html
>>
>> One user also used series resistors to solve the problem. As
>> far as I can see there is a pullup needed anyway, to avoid
>> detecting a break condition on the UART line. Could this also
>> be a problem? Moving from high-impedance to high at a time
>> defined by SYSEN (or a little bit after that) seems a bit unsafe.
>>
>> --
>> View this message in context:
>> http://gumstix.8.n6.nabble.com/Protecting-UART-ports-while-SYS
>> EN-is-low-tp3274358p3511548.html
>> Sent from the Gumstix mailing list archive at Nabble.com.
>>
>> --------------------------------------------------------------
>> ----------------
>> Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't
>> need a complex infrastructure or vast IT resources to deliver
>> seamless, secure access to virtual desktops. With this
>> all-in-one solution, easily deploy virtual desktops for less
>> than the cost of PCs and save 60% on VDI infrastructure
>> costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox
>> _______________________________________________
>> gumstix-users mailing list
>> [hidden email]
>> https://lists.sourceforge.net/lists/listinfo/gumstix-users
>>
>> ______________________________________________________________________
>> CAUTION: This message was sent via the Public Internet and
>> its authenticity cannot be guaranteed.
>>
>
> PROPRIETARY: This e-mail contains proprietary information some or all of which may be legally privileged.  It is intended for the recipient only.  If an addressing or transmission error has misdirected this e-mail, please notify the authority by replying to this e-mail.  If you are not the intended recipient you must not use, disclose, distribute, copy, print, or rely on this e-mail.
>
> ------------------------------------------------------------------------------
> Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a complex
> infrastructure or vast IT resources to deliver seamless, secure access to
> virtual desktops. With this all-in-one solution, easily deploy virtual
> desktops for less than the cost of PCs and save 60% on VDI infrastructure
> costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox
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Re: Protecting UART ports while SYSEN is low

Keane, Ben (STRX)
Excellent, thanks. Will make modifications to our hardware design to make sure this is the case.

Has anyone measured how long it normally takes for the SYSEN line to go HIGH on startup?

> -----Original Message-----
> From: Arlen Raasch [mailto:[hidden email]]
> Sent: Tuesday, 10 January 2012 11:56 PM
> To: General mailing list for gumstix users.
> Subject: Re: [Gumstix-users] Protecting UART ports while SYSEN is low
>
> Ben:
>
> The OMAP processor expects all I/O lines to be driven only
> after the proper power up sequence has completed, and that
> all I/O lines to the OMAP processor stop being driven before
> the proper power down sequence begins.
>
> If you choose to drive any I/O lines before the power up
> sequence has started, or continue to do so while shutting
> power off to the processor,  you are using the OMAP processor
> out of the manufacturer recommendations, and TI does not
> define how the device will behave.
>
> Thus, it is a good idea to not use the device in this way.
>
> The TI TPS65950 Power Management IC provides the SYSEN signal
> that goes high when it is allowable to start driving the I/O lines.
>
> Use this signal to enable driving all I/O to the OMAP
> processor, and you will be fine.
>
> Thanks,
>
> -Arlen
>
> On Mon, Jan 9, 2012 at 6:01 PM, Keane, Ben (STRX)
> <[hidden email]> wrote:
> > Is this protection only required for UART or for all GPIO pins?
> >
> >> -----Original Message-----
> >> From: ebtschi [mailto:[hidden email]]
> >> Sent: Monday, 9 January 2012 8:13 PM
> >> To: [hidden email]
> >> Subject: Re: [Gumstix-users] Protecting UART ports while
> SYSEN is low
> >>
> >> Hi Lucas,
> >>
> >> thank you for your reply.
> >>
> >> I also found this thread:
> >> http://gumstix.8.n6.nabble.com/Overo-module-seems-dead-root-ca
> >> use-td641684.html
> >>
> >> One user also used series resistors to solve the problem.
> As far as I
> >> can see there is a pullup needed anyway, to avoid
> detecting a break
> >> condition on the UART line. Could this also be a problem?
> Moving from
> >> high-impedance to high at a time defined by SYSEN (or a little bit
> >> after that) seems a bit unsafe.
> >>
> >> --
> >> View this message in context:
> >> http://gumstix.8.n6.nabble.com/Protecting-UART-ports-while-SYS
> >> EN-is-low-tp3274358p3511548.html
> >> Sent from the Gumstix mailing list archive at Nabble.com.
> >>
> >> --------------------------------------------------------------
> >> ----------------
> >> Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a
> >> complex infrastructure or vast IT resources to deliver seamless,
> >> secure access to virtual desktops. With this all-in-one solution,
> >> easily deploy virtual desktops for less than the cost of
> PCs and save
> >> 60% on VDI infrastructure costs. Try it free!
> >> http://p.sf.net/sfu/Citrix-VDIinabox
> >> _______________________________________________
> >> gumstix-users mailing list
> >> [hidden email]
> >> https://lists.sourceforge.net/lists/listinfo/gumstix-users
> >>
> >>
> _____________________________________________________________________
> >> _
> >> CAUTION: This message was sent via the Public Internet and its
> >> authenticity cannot be guaranteed.
> >>
> >
> > PROPRIETARY: This e-mail contains proprietary information
> some or all of which may be legally privileged.  It is
> intended for the recipient only.  If an addressing or
> transmission error has misdirected this e-mail, please notify
> the authority by replying to this e-mail.  If you are not the
> intended recipient you must not use, disclose, distribute,
> copy, print, or rely on this e-mail.
> >
> >
> ----------------------------------------------------------------------
> > -------- Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't
> > need a complex infrastructure or vast IT resources to deliver
> > seamless, secure access to virtual desktops. With this all-in-one
> > solution, easily deploy virtual desktops for less than the
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> > and save 60% on VDI infrastructure costs. Try it free!
> > http://p.sf.net/sfu/Citrix-VDIinabox
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>
> --------------------------------------------------------------
> ----------------
> Write once. Port to many.
> Get the SDK and tools to simplify cross-platform app
> development. Create new or port existing apps to sell to
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PROPRIETARY: This e-mail contains proprietary information some or all of which may be legally privileged.  It is intended for the recipient only.  If an addressing or transmission error has misdirected this e-mail, please notify the authority by replying to this e-mail.  If you are not the intended recipient you must not use, disclose, distribute, copy, print, or rely on this e-mail.

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Re: Protecting UART ports while SYSEN is low

sturnfie
Keane, Ben (STRX) wrote
Excellent, thanks. Will make modifications to our hardware design to make sure this is the case.

Has anyone measured how long it normally takes for the SYSEN line to go HIGH on startup?
Datasheet has the measurements. ~2ms.

Section 4.5.3.3 OMAP3 Power-On Sequence
http://www.ti.com/lit/ds/symlink/tps65950.pdf

Lucas
--
Lucas Sturnfield
sturnfie@gmail.com