Re: [beagleboard] Switching a GPIO to and LED via the device tree

[TJF]

The output lines in a GPIO subsystem are limited to a maximum current of 6 
mA. The users/students should know that they need a low power/current LED 
for your circuit.

The value of the current limiting resistor depends on the threshold voltage 
of the LED, which depends on the LED color. 220Ω is OK for a blue LED, but 
too small for ie. an orange LED with 1V65 threshold / 6mA. This may damage 
the LED, or - most likely - the output line in the GPIO subsystem (= the BB 
CPU).

Regards

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Jim F]

Mark,

I wish more tutorials looked like this. I should have started with
congratulations on a great job. Thanks for considering my suggestions.

Best,
Jim

On Fri, Aug 28, 2020, 5:33 PM Mark A. Yoder  wrote:

> Jim:
>   Thanks for the feedback.  I like your suggestions.  Responses below:
>
> On Thursday, August 27, 2020 at 2:17:24 PM UTC-4 jimf...@gmail.com wrote:
>
>> Hi Mark,
>>
>> Nice tutorial. Wish I'd had that quite some time ago, I had to pull all
>> those pieces together myself.
>>
>> From having read a bunch of posts here, I have a few suggestions for your
>> consideration.
>>
>> 1. User needs to be in the gpio group. This isn't mentioned.
>>
> *The debian image has user debian in the gpio group by default.  Though
> there are other use cases, I want to keep this focused on my students.*
> *They are fighting too many alligators for me to add the group alligator.*
>
>> 2. People often ignore parts of instructions. If your prompt included the
>> current directory name, it would be slightly more obvious where each
>> command is run.
>>
> *Good suggestion.  To keep the clutter down I just converted all paths to
> absolute.  Does that work?*
>
>> 3. It would be AMAZING if tutorials such as these included a description
>> of what version of code this was developed/tested on. You could either
>> mention the RCN release number or the kernel build, but it would be so
>> great if this were a standard thing to mention. Consider how much things
>> have changed with device trees over the past five (?) years. There's tons
>> of now-wrong notes on how to do things. (I know you mention a kernel in the
>> compilation section, I guess it would be nice to spell this out up top,
>> i.e. "This tutorial is applicable to Beaglebone release xxx").
>>
> *Great idea.  Wiki pages age so quickly.   I've added a footnote that
> displays the output of uname and cat /etc/dogtag.  What do you think?*
> (https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED)
>
>> 4. Not sure this comment is welcome, but a top level Tutorials page
>> containing all the EBC## tutorials would be cool. I found the others by
>> clicking on your ECE497 link, but that isn't exactly obvious (to me). Those
>> look like some great materials that I hadn't come across before, for some
>> reason.
>>
> *Another good idea, but...  I'm sticking with using the Category to
> collect all my pages.  I hope my titles are descriptive enough that I can
> remember what's in them.*
>
> Thanks again for the feedback.
>
> --Mark
>
>
>> Best,
>>
>> Jim
>>
>> On Wed, Aug 26, 2020 at 10:23 PM Mark A. Yoder 
>> wrote:
>>
>>> Beagler's:
>>>   I just wrote up some notes on how to edit the device tree to change a
>>> GPIO into an LED.
>>>
>>> Switching_a_GPIO_to_an_LED
>>> 
>>>
>>> It's are rather involved process that requires understanding some deeper
>>> magic.
>>>
>>> Let me know what you think.
>>>
>>> --Mark
>>>
>>> --
>>>
>> For more options, visit http://beagleboard.org/discuss
>>> ---
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>>> Groups "BeagleBoard" group.
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>>> 
>>> .
>>>
>> --
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> 
> .
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Mark A. Yoder]

Jim:
  Thanks for the feedback.  I like your suggestions.  Responses below:

On Thursday, August 27, 2020 at 2:17:24 PM UTC-4 jimf...@gmail.com wrote:

> Hi Mark,
>
> Nice tutorial. Wish I'd had that quite some time ago, I had to pull all 
> those pieces together myself.
>
> From having read a bunch of posts here, I have a few suggestions for your 
> consideration.
>
> 1. User needs to be in the gpio group. This isn't mentioned.
>
*The debian image has user debian in the gpio group by default.  Though 
there are other use cases, I want to keep this focused on my students.*
*They are fighting too many alligators for me to add the group alligator.*

> 2. People often ignore parts of instructions. If your prompt included the 
> current directory name, it would be slightly more obvious where each 
> command is run. 
>
*Good suggestion.  To keep the clutter down I just converted all paths to 
absolute.  Does that work?* 

> 3. It would be AMAZING if tutorials such as these included a description 
> of what version of code this was developed/tested on. You could either 
> mention the RCN release number or the kernel build, but it would be so 
> great if this were a standard thing to mention. Consider how much things 
> have changed with device trees over the past five (?) years. There's tons 
> of now-wrong notes on how to do things. (I know you mention a kernel in the 
> compilation section, I guess it would be nice to spell this out up top, 
> i.e. "This tutorial is applicable to Beaglebone release xxx").
>
*Great idea.  Wiki pages age so quickly.   I've added a footnote that 
displays the output of uname and cat /etc/dogtag.  What do you think?* 
(https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED)

> 4. Not sure this comment is welcome, but a top level Tutorials page 
> containing all the EBC## tutorials would be cool. I found the others by 
> clicking on your ECE497 link, but that isn't exactly obvious (to me). Those 
> look like some great materials that I hadn't come across before, for some 
> reason.
>
*Another good idea, but...  I'm sticking with using the Category to collect 
all my pages.  I hope my titles are descriptive enough that I can remember 
what's in them.* 

Thanks again for the feedback.

--Mark


> Best,
>
> Jim
>
> On Wed, Aug 26, 2020 at 10:23 PM Mark A. Yoder  
> wrote:
>
>> Beagler's:
>>   I just wrote up some notes on how to edit the device tree to change a 
>> GPIO into an LED.
>>
>> Switching_a_GPIO_to_an_LED 
>> 
>>
>> It's are rather involved process that requires understanding some deeper 
>> magic.
>>
>> Let me know what you think.
>>
>> --Mark
>>
>> -- 
>>
> For more options, visit http://beagleboard.org/discuss
>> --- 
>> You received this message because you are subscribed to the Google Groups 
>> "BeagleBoard" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to beagleboard...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>>  
>> 
>> .
>>
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Ren W]

*> tutorials such as these included a description of what version of code 
this was developed/tested on.*

This ^
As a beginner, it's been quite frustrating to have to wade through all the 
tutorials referring to a cape manager that no longer exists.
Not only have I learnt how things work today, I've also had to learn how 
they used to work — which I could have done without. 


On Thursday, August 27, 2020 at 11:17:24 AM UTC-7 jimf...@gmail.com wrote:

> Hi Mark,
>
> Nice tutorial. Wish I'd had that quite some time ago, I had to pull all 
> those pieces together myself.
>
> From having read a bunch of posts here, I have a few suggestions for your 
> consideration.
>
> 1. User needs to be in the gpio group. This isn't mentioned.
> 2. People often ignore parts of instructions. If your prompt included the 
> current directory name, it would be slightly more obvious where each 
> command is run. 
> 3. It would be AMAZING if tutorials such as these included a description 
> of what version of code this was developed/tested on. You could either 
> mention the RCN release number or the kernel build, but it would be so 
> great if this were a standard thing to mention. Consider how much things 
> have changed with device trees over the past five (?) years. There's tons 
> of now-wrong notes on how to do things. (I know you mention a kernel in the 
> compilation section, I guess it would be nice to spell this out up top, 
> i.e. "This tutorial is applicable to Beaglebone release xxx").
> 4. Not sure this comment is welcome, but a top level Tutorials page 
> containing all the EBC## tutorials would be cool. I found the others by 
> clicking on your ECE497 link, but that isn't exactly obvious (to me). Those 
> look like some great materials that I hadn't come across before, for some 
> reason.
>
> Best,
>
> Jim
>
> On Wed, Aug 26, 2020 at 10:23 PM Mark A. Yoder  
> wrote:
>
>> Beagler's:
>>   I just wrote up some notes on how to edit the device tree to change a 
>> GPIO into an LED.
>>
>> Switching_a_GPIO_to_an_LED 
>> 
>>
>> It's are rather involved process that requires understanding some deeper 
>> magic.
>>
>> Let me know what you think.
>>
>> --Mark
>>
>> -- 
>>
> For more options, visit http://beagleboard.org/discuss
>> --- 
>> You received this message because you are subscribed to the Google Groups 
>> "BeagleBoard" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to beagleboard...@googlegroups.com.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>>  
>> 
>> .
>>
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Jim F]

Hi Mark,

Nice tutorial. Wish I'd had that quite some time ago, I had to pull all
those pieces together myself.

>From having read a bunch of posts here, I have a few suggestions for your
consideration.

1. User needs to be in the gpio group. This isn't mentioned.
2. People often ignore parts of instructions. If your prompt included the
current directory name, it would be slightly more obvious where each
command is run.
3. It would be AMAZING if tutorials such as these included a description of
what version of code this was developed/tested on. You could either mention
the RCN release number or the kernel build, but it would be so great if
this were a standard thing to mention. Consider how much things have
changed with device trees over the past five (?) years. There's tons of
now-wrong notes on how to do things. (I know you mention a kernel in the
compilation section, I guess it would be nice to spell this out up top,
i.e. "This tutorial is applicable to Beaglebone release xxx").
4. Not sure this comment is welcome, but a top level Tutorials page
containing all the EBC## tutorials would be cool. I found the others by
clicking on your ECE497 link, but that isn't exactly obvious (to me). Those
look like some great materials that I hadn't come across before, for some
reason.

Best,

Jim

On Wed, Aug 26, 2020 at 10:23 PM Mark A. Yoder 
wrote:

> Beagler's:
>   I just wrote up some notes on how to edit the device tree to change a
> GPIO into an LED.
>
> Switching_a_GPIO_to_an_LED
> 
>
> It's are rather involved process that requires understanding some deeper
> magic.
>
> Let me know what you think.
>
> --Mark
>
> --
> For more options, visit http://beagleboard.org/discuss
> ---
> You received this message because you are subscribed to the Google Groups
> "BeagleBoard" group.
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> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
> 
> .
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Mark A. Yoder]

Jon:
  Thanks for the suggestions.  I'll address each in line..

--Mark

On Thursday, August 27, 2020 at 12:11:56 PM UTC-4 jonn...@gmail.com wrote:

> Very cool Mark.
>
> A couple of notes:
> 1.  It might be a good idea to put a note in there for the folks to back 
> up their currently booted dts/dtb files before editing them.
>  *Good idea, but this is a git repo, so I added the following: *
> https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED#Recovering_from_a_miss-edit
> 2. Under "Finding which device tree to edit" I believe there is a typo:
>  Note: If you want to edit the source using cloud9 us the following 
> trick ...
>Should be:
>  Note: If you want to edit the source using cloud9 *use* the 
> following trick ...
> *Fixed.  Thanks.*
> 3. When you run make, would it be best to just run it against the file 
> that was edited rather than the whole folder?
>  Maybe the build script is smart enough to figure this out.
> *You can do the individual file, but it more typing.  I guess I'm lazy.  
> And it still installs everything.*
> 4.  Under "Adding our LED" there is the following without explaining the 
> why.  Was this intentional?
> "How did I know to use *gpio1* and *18*?"
> *That was intentional to get my students to think a bit.  Should I include 
> the answer for the broader **audience**? *
> This is a nice series.  Thanks for sharing.
>
> Cheers,
>
> Jon
>
> On Thu, Aug 27, 2020 at 8:31 AM Renaud Waldura  wrote:
>
>> Good stuff, thank you Mark!
>>
>> How are the triggers defined? They're more or less self explanatory, I'm 
>> just curious how it works.
>>
>>
>> On Thu, Aug 27, 2020, 6:06 AM Mark A. Yoder  wrote:
>>
>>>
>>> Yup, years for facing blank stares has taught me a few things.
>>>
>>> This particular example touched on so many different things it could be 
>>> a nice final exam.
>>>
>>> --Mark
>>> On Wednesday, August 26, 2020 at 9:59:23 PM UTC-4 lazarman wrote:
>>>

 Well presented I like your approach at documentation I bet that comes 
 from teaching 


 Sent from Yahoo Mail on Android 
 

 On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder
  wrote:

 Beagler's:
   I just wrote up some notes on how to edit the device tree to change a 
 GPIO into an LED.

 Switching_a_GPIO_to_an_LED 
 

 It's are rather involved process that requires understanding some 
 deeper magic.

 Let me know what you think.

 --Mark

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 .

 -- 
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>>>  
>>> 
>>> .
>>>
>> -- 
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>>  
>> 
>> .
>>
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[jonnymo]

Very cool Mark.

A couple of notes:
1.  It might be a good idea to put a note in there for the folks to back up
their currently booted dts/dtb files before editing them.

2. Under "Finding which device tree to edit" I believe there is a typo:
 Note: If you want to edit the source using cloud9 us the following
trick ...
   Should be:
 Note: If you want to edit the source using cloud9 *use* the following
trick ...

3. When you run make, would it be best to just run it against the file that
was edited rather than the whole folder?
 Maybe the build script is smart enough to figure this out.

4.  Under "Adding our LED" there is the following without explaining the
why.  Was this intentional?
"How did I know to use *gpio1* and *18*?"

This is a nice series.  Thanks for sharing.

Cheers,

Jon

On Thu, Aug 27, 2020 at 8:31 AM Renaud Waldura  wrote:

> Good stuff, thank you Mark!
>
> How are the triggers defined? They're more or less self explanatory, I'm
> just curious how it works.
>
>
> On Thu, Aug 27, 2020, 6:06 AM Mark A. Yoder 
> wrote:
>
>>
>> Yup, years for facing blank stares has taught me a few things.
>>
>> This particular example touched on so many different things it could be a
>> nice final exam.
>>
>> --Mark
>> On Wednesday, August 26, 2020 at 9:59:23 PM UTC-4 lazarman wrote:
>>
>>>
>>> Well presented I like your approach at documentation I bet that comes
>>> from teaching
>>>
>>>
>>> Sent from Yahoo Mail on Android
>>> 
>>>
>>> On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder
>>>  wrote:
>>>
>>> Beagler's:
>>>   I just wrote up some notes on how to edit the device tree to change a
>>> GPIO into an LED.
>>>
>>> Switching_a_GPIO_to_an_LED
>>> 
>>>
>>> It's are rather involved process that requires understanding some deeper
>>> magic.
>>>
>>> Let me know what you think.
>>>
>>> --Mark
>>>
>>> --
>>> For more options, visit http://beagleboard.org/discuss
>>> ---
>>> You received this message because you are subscribed to the Google
>>> Groups "BeagleBoard" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to beagleboard...@googlegroups.com.
>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>>> 
>>> .
>>>
>>> --
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>> 
>> .
>>
> --
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>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Mark A. Yoder]

Ren:
  Good question.  I poked around the kernel source 

 a 
bit hoping to create an example for my students.  
But it was more complicated than what I wanted for my students.

--Mark

On Thursday, August 27, 2020 at 11:30:59 AM UTC-4 Ren W wrote:

> Good stuff, thank you Mark!
>
> How are the triggers defined? They're more or less self explanatory, I'm 
> just curious how it works.
>
>
> On Thu, Aug 27, 2020, 6:06 AM Mark A. Yoder  wrote:
>
>>
>> Yup, years for facing blank stares has taught me a few things.
>>
>> This particular example touched on so many different things it could be a 
>> nice final exam.
>>
>> --Mark
>> On Wednesday, August 26, 2020 at 9:59:23 PM UTC-4 lazarman wrote:
>>
>>>
>>> Well presented I like your approach at documentation I bet that comes 
>>> from teaching 
>>>
>>>
>>> Sent from Yahoo Mail on Android 
>>> 
>>>
>>> On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder
>>>  wrote:
>>>
>>> Beagler's:
>>>   I just wrote up some notes on how to edit the device tree to change a 
>>> GPIO into an LED.
>>>
>>> Switching_a_GPIO_to_an_LED 
>>> 
>>>
>>> It's are rather involved process that requires understanding some deeper 
>>> magic.
>>>
>>> Let me know what you think.
>>>
>>> --Mark
>>>
>>> -- 
>>> For more options, visit http://beagleboard.org/discuss
>>> --- 
>>> You received this message because you are subscribed to the Google 
>>> Groups "BeagleBoard" group.
>>> To unsubscribe from this group and stop receiving emails from it, send 
>>> an email to beagleboard...@googlegroups.com.
>>> To view this discussion on the web visit 
>>> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>>>  
>>> 
>>> .
>>>
>>> -- 
>> For more options, visit http://beagleboard.org/discuss
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>>
> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/beagleboard/6203e02e-107b-4404-b952-0ef40ad12118n%40googlegroups.com
>>  
>> 
>> .
>>
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Renaud Waldura]

Good stuff, thank you Mark!

How are the triggers defined? They're more or less self explanatory, I'm
just curious how it works.


On Thu, Aug 27, 2020, 6:06 AM Mark A. Yoder  wrote:

>
> Yup, years for facing blank stares has taught me a few things.
>
> This particular example touched on so many different things it could be a
> nice final exam.
>
> --Mark
> On Wednesday, August 26, 2020 at 9:59:23 PM UTC-4 lazarman wrote:
>
>>
>> Well presented I like your approach at documentation I bet that comes
>> from teaching
>>
>>
>> Sent from Yahoo Mail on Android
>> 
>>
>> On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder
>>  wrote:
>>
>> Beagler's:
>>   I just wrote up some notes on how to edit the device tree to change a
>> GPIO into an LED.
>>
>> Switching_a_GPIO_to_an_LED
>> 
>>
>> It's are rather involved process that requires understanding some deeper
>> magic.
>>
>> Let me know what you think.
>>
>> --Mark
>>
>> --
>> For more options, visit http://beagleboard.org/discuss
>> ---
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>> "BeagleBoard" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to beagleboard...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>> 
>> .
>>
>> --
> For more options, visit http://beagleboard.org/discuss
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> 
> .
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

[Mark A. Yoder]

Yup, years for facing blank stares has taught me a few things.

This particular example touched on so many different things it could be a 
nice final exam.

--Mark
On Wednesday, August 26, 2020 at 9:59:23 PM UTC-4 lazarman wrote:

>
> Well presented I like your approach at documentation I bet that comes from 
> teaching 
>
>
> Sent from Yahoo Mail on Android 
> 
>
> On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder
>  wrote:
>
> Beagler's:
>   I just wrote up some notes on how to edit the device tree to change a 
> GPIO into an LED.
>
> Switching_a_GPIO_to_an_LED 
> 
>
> It's are rather involved process that requires understanding some deeper 
> magic.
>
> Let me know what you think.
>
> --Mark
>
> -- 
> For more options, visit http://beagleboard.org/discuss
> --- 
> You received this message because you are subscribed to the Google Groups 
> "BeagleBoard" group.
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> email to beagleboard...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/beagleboard/61317cde-fb07-4c98-bc56-c968e58e7a10n%40googlegroups.com
>  
> 
> .
>
>

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Re: [beagleboard] Switching a GPIO to and LED via the device tree

['Mark Lazarewicz' via BeagleBoard]

Well presented I like your approach at documentation I bet that comes from 
teaching 

Sent from Yahoo Mail on Android 
 
  On Wed, Aug 26, 2020 at 5:30 PM, Mark A. Yoder wrote: 
  Beagler's:  I just wrote up some notes on how to edit the device tree to 
change a GPIO into an LED.
Switching_a_GPIO_to_an_LED

It's are rather involved process that requires understanding some deeper magic.
Let me know what you think.
--Mark

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[beagleboard] Switching a GPIO to and LED via the device tree

[Mark A. Yoder]

Beagler's:
  I just wrote up some notes on how to edit the device tree to change a 
GPIO into an LED.

Switching_a_GPIO_to_an_LED 


It's are rather involved process that requires understanding some deeper 
magic.

Let me know what you think.

--Mark

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