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Question about Linux and PTP over USB spec support

Laplante, Patrick

All,

 

I have tons of experience with DSC (PTP over USB) on NetBSD (also Pictbridge).  Like you all know PictBridge involves lots of sending to the camera.  Now the PTP over USB spec stated that if the data being sent to the camera is a multiplier of the bulk fifo size, the pc must send a zero length packet.  Well on BSD, the only way to easy do that was writing a kernel driver (easy to do).

 

Now, on Linux, I don’t see any specific driver.  I am wondering how is the zero length packet being sent to the device.  Is it part of the usb stact default behavior?  How can it know if a packet is the last one?

 

Just wondering.

 

 

Pat Laplante
Principal Engineer

Vanteon Corporation
2851 Clover Street
Pittsford, NY 14534-1711
Office: (585) 248-0510 x298
Fax: (585) 248-0537
www.vanteon.com - Embedded for Your Future

 

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RE: Question about Linux and PTP over USB spec support

Laplante, Patrick

I did some research today and discovered:

 

The linux usb host stack use URB to allow user land app to read and write to a usb device.   One of the flag is to specify sending a ZEROLENGTH packet to the device.  Now looking at the libusb source code, I can’t find anywhere in the linux.c file where they are doing that.  Is this on by default in the kernel or is it a bug in libusb or am I missing something?

 

Thanks

 

Pat

 


From: [hidden email] [mailto:[hidden email]] On Behalf Of Patrick Laplante
Sent: Sunday, March 05, 2006 9:21 AM
To: [hidden email]
Subject: [gphoto-devel] Question about Linux and PTP over USB spec support

 

All,

 

I have tons of experience with DSC (PTP over USB) on NetBSD (also Pictbridge).  Like you all know PictBridge involves lots of sending to the camera.  Now the PTP over USB spec stated that if the data being sent to the camera is a multiplier of the bulk fifo size, the pc must send a zero length packet.  Well on BSD, the only way to easy do that was writing a kernel driver (easy to do).

 

Now, on Linux, I don’t see any specific driver.  I am wondering how is the zero length packet being sent to the device.  Is it part of the usb stact default behavior?  How can it know if a packet is the last one?

 

Just wondering.

 

 

Pat Laplante
Principal Engineer

Vanteon Corporation
2851 Clover Street
Pittsford, NY 14534-1711
Office: (585) 248-0510 x298
Fax: (585) 248-0537
www.vanteon.com - Embedded for Your Future

 

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Re: Question about Linux and PTP over USB spec support

Marcus Meissner-4
In reply to this post by Laplante, Patrick
On Sun, Mar 05, 2006 at 09:20:35AM -0500, Patrick Laplante wrote:

> All,
>
>  
>
> I have tons of experience with DSC (PTP over USB) on NetBSD (also
> Pictbridge).  Like you all know PictBridge involves lots of sending to the
> camera.  Now the PTP over USB spec stated that if the data being sent to the
> camera is a multiplier of the bulk fifo size, the pc must send a zero length
> packet.  Well on BSD, the only way to easy do that was writing a kernel
> driver (easy to do).

Actuallay they also mention "short writes" ?
 
> Now, on Linux, I don't see any specific driver.  I am wondering how is the
> zero length packet being sent to the device.  Is it part of the usb stact
> default behavior?  How can it know if a packet is the last one?

Most PTP cameras do not care about it, so they work fine.

MTP devices on the other hand have problems with it.

Ciao, Marcus


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Re: Question about Linux and PTP over USB spec support

Marcus Meissner-4
In reply to this post by Laplante, Patrick
On Sun, Mar 05, 2006 at 07:55:08PM -0500, Patrick Laplante wrote:
> I did some research today and discovered:
>
>  
>
> The linux usb host stack use URB to allow user land app to read and write to
> a usb device.   One of the flag is to specify sending a ZEROLENGTH packet to
> the device.  Now looking at the libusb source code, I can't find anywhere in
> the linux.c file where they are doing that.  Is this on by default in the
> kernel or is it a bug in libusb or am I missing something?

It is a missing feature in libusb.

However I think it is possible to send a 0 sized URB to the kernel
folllowing the codepaths, which might have the same effect.

Ciao, Marcus


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RE: Question about Linux and PTP over USB spec support

Laplante, Patrick
In reply to this post by Marcus Meissner-4
Marcus,

Thanks for the reply!

Yeah short write really is a way to tell the camera that you are done
sending data to it.  A camera that follows the DSC (Digital Still Camera)
USB spec should treat short packet as the end of a PTP phase (Command or
Data).  But sometime if the amount of data being sent is the exact size or a
multiplier of the fifo, then you need a way to tell the camera that you are
done sending data (that is per spec) which is where the zero length packet
comes into play.

I did lots of PTP work with probably most if not all of the Kodak camera and
they all (or most of them) require that short packet.  It was also an issue
with Pictbridge camera (I did lots of works with the PictBridge protocol on
the Initiator side of the world 'printer').

So if I hear you correctly, I will need to add a feature to the libusb
write.  Probably a flag that specifies whether a short packet needs to be
sent after the write completes.

I am asking because I am starting a new project where I need to implement
the PictBridge print part on a device running Linux (no gphoto involve in
this).  But I was thinking of using libptp for the ptp stack.

Anyway, Thanks for your help.


-----Original Message-----
From: Marcus Meissner [mailto:[hidden email]]
Sent: Monday, March 06, 2006 1:32 AM
To: Patrick Laplante
Cc: [hidden email]
Subject: Re: [gphoto-devel] Question about Linux and PTP over USB spec
support

On Sun, Mar 05, 2006 at 09:20:35AM -0500, Patrick Laplante wrote:
> All,
>
>  
>
> I have tons of experience with DSC (PTP over USB) on NetBSD (also
> Pictbridge).  Like you all know PictBridge involves lots of sending to the
> camera.  Now the PTP over USB spec stated that if the data being sent to
the
> camera is a multiplier of the bulk fifo size, the pc must send a zero
length
> packet.  Well on BSD, the only way to easy do that was writing a kernel
> driver (easy to do).

Actuallay they also mention "short writes" ?
 
> Now, on Linux, I don't see any specific driver.  I am wondering how is the
> zero length packet being sent to the device.  Is it part of the usb stact
> default behavior?  How can it know if a packet is the last one?

Most PTP cameras do not care about it, so they work fine.

MTP devices on the other hand have problems with it.

Ciao, Marcus



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Re: Question about Linux and PTP over USB spec support

Marcus Meissner-4
In reply to this post by Marcus Meissner-4
On Mon, Mar 06, 2006 at 10:05:36AM -0500, Patrick Laplante wrote:

> Marcus,
>
> Thanks for the reply!
>
> Yeah short write really is a way to tell the camera that you are done
> sending data to it.  A camera that follows the DSC (Digital Still Camera)
> USB spec should treat short packet as the end of a PTP phase (Command or
> Data).  But sometime if the amount of data being sent is the exact size or a
> multiplier of the fifo, then you need a way to tell the camera that you are
> done sending data (that is per spec) which is where the zero length packet
> comes into play.

Yes. I think the reason why we are not seeing this with normal cameras
is that we never send such packages. (for cameras we send command packets,
all smaller than 64? 512? bytes,  and property values, same).

MTP devices have more sizes to send, thats why we are seeing more problems there
I think.

> I did lots of PTP work with probably most if not all of the Kodak camera and
> they all (or most of them) require that short packet.  It was also an issue
> with Pictbridge camera (I did lots of works with the PictBridge protocol on
> the Initiator side of the world 'printer').
>
> So if I hear you correctly, I will need to add a feature to the libusb
> write.  Probably a flag that specifies whether a short packet needs to be
> sent after the write completes.

I think so, or a null packet.

Your help there would be very useful.

> I am asking because I am starting a new project where I need to implement
> the PictBridge print part on a device running Linux (no gphoto involve in
> this).  But I was thinking of using libptp for the ptp stack.

You could just involve libgphoto2, but libptp might be more useful, especially
when runnining it in a some kind of polling mode.
 
Ciao, Marcus


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RE: Question about Linux and PTP over USB spec support

Laplante, Patrick
Marcus,

I'll be happy to add the zero length stuff to libusb and libptp....

I have a camera where I can do some custom PTP command on it to try it out.

Once I have something working, I'll let you guys know.

Pat

-----Original Message-----
From: Marcus Meissner [mailto:[hidden email]]
Sent: Monday, March 06, 2006 3:57 PM
To: Patrick Laplante
Cc: [hidden email]
Subject: Re: [gphoto-devel] Question about Linux and PTP over USB spec
support

On Mon, Mar 06, 2006 at 10:05:36AM -0500, Patrick Laplante wrote:
> Marcus,
>
> Thanks for the reply!
>
> Yeah short write really is a way to tell the camera that you are done
> sending data to it.  A camera that follows the DSC (Digital Still Camera)
> USB spec should treat short packet as the end of a PTP phase (Command or
> Data).  But sometime if the amount of data being sent is the exact size or
a
> multiplier of the fifo, then you need a way to tell the camera that you
are
> done sending data (that is per spec) which is where the zero length packet
> comes into play.

Yes. I think the reason why we are not seeing this with normal cameras
is that we never send such packages. (for cameras we send command packets,
all smaller than 64? 512? bytes,  and property values, same).

MTP devices have more sizes to send, thats why we are seeing more problems
there
I think.

> I did lots of PTP work with probably most if not all of the Kodak camera
and
> they all (or most of them) require that short packet.  It was also an
issue
> with Pictbridge camera (I did lots of works with the PictBridge protocol
on
> the Initiator side of the world 'printer').
>
> So if I hear you correctly, I will need to add a feature to the libusb
> write.  Probably a flag that specifies whether a short packet needs to be
> sent after the write completes.

I think so, or a null packet.

Your help there would be very useful.

> I am asking because I am starting a new project where I need to implement
> the PictBridge print part on a device running Linux (no gphoto involve in
> this).  But I was thinking of using libptp for the ptp stack.

You could just involve libgphoto2, but libptp might be more useful,
especially
when runnining it in a some kind of polling mode.
 
Ciao, Marcus



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RE: Question about Linux and PTP over USB spec support

Laplante, Patrick
One Important thing is getting the device FIFO size.  This is available in
the USB Device descriptor.

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Patrick
Laplante
Sent: Monday, March 06, 2006 4:30 PM
To: 'Marcus Meissner'
Cc: [hidden email]
Subject: RE: [gphoto-devel] Question about Linux and PTP over USB spec
support

Marcus,

I'll be happy to add the zero length stuff to libusb and libptp....

I have a camera where I can do some custom PTP command on it to try it out.

Once I have something working, I'll let you guys know.

Pat

-----Original Message-----
From: Marcus Meissner [mailto:[hidden email]]
Sent: Monday, March 06, 2006 3:57 PM
To: Patrick Laplante
Cc: [hidden email]
Subject: Re: [gphoto-devel] Question about Linux and PTP over USB spec
support

On Mon, Mar 06, 2006 at 10:05:36AM -0500, Patrick Laplante wrote:
> Marcus,
>
> Thanks for the reply!
>
> Yeah short write really is a way to tell the camera that you are done
> sending data to it.  A camera that follows the DSC (Digital Still Camera)
> USB spec should treat short packet as the end of a PTP phase (Command or
> Data).  But sometime if the amount of data being sent is the exact size or
a
> multiplier of the fifo, then you need a way to tell the camera that you
are
> done sending data (that is per spec) which is where the zero length packet
> comes into play.

Yes. I think the reason why we are not seeing this with normal cameras
is that we never send such packages. (for cameras we send command packets,
all smaller than 64? 512? bytes,  and property values, same).

MTP devices have more sizes to send, thats why we are seeing more problems
there
I think.

> I did lots of PTP work with probably most if not all of the Kodak camera
and
> they all (or most of them) require that short packet.  It was also an
issue
> with Pictbridge camera (I did lots of works with the PictBridge protocol
on
> the Initiator side of the world 'printer').
>
> So if I hear you correctly, I will need to add a feature to the libusb
> write.  Probably a flag that specifies whether a short packet needs to be
> sent after the write completes.

I think so, or a null packet.

Your help there would be very useful.

> I am asking because I am starting a new project where I need to implement
> the PictBridge print part on a device running Linux (no gphoto involve in
> this).  But I was thinking of using libptp for the ptp stack.

You could just involve libgphoto2, but libptp might be more useful,
especially
when runnining it in a some kind of polling mode.
 
Ciao, Marcus



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Re: Question about Linux and PTP over USB spec support

Sean Hsu
In reply to this post by Laplante, Patrick
Hi guys:
After reading your guys' post, I hope I can get some feedback here.
My goal is to establish a connection between freescale iMX6qdl-sabresd Linux OS device and Windows PC using PTP(Picture Transfer Protocol) with USB cable. However, I do not even know how to start. I list my questions as below, please let me know if any of you knows the answer.
1. If any of you are familiar with freescale board, local.conf is the file that is used to add packages.
    If what I need is to import some packages, what packages should I include? gphoto2, libptp? etc,. ?
2. I know now PTP is the transport layer above the USB-IF physical layer. What should I do to enable the USB-IF and send PTP protocol? This involves a lot of self-coding. The best way is to find a library or packages that I can import to the freescale board and start using the PTP.
3. If what I am trying to do is too complicated, I am not insist on doing it. However, I do want a linux and Windows connection with PTP or MTP using USB cable. Importing packages or libraries seem to be the best way to get started.

Any ideas or concepts about what I mentioned above will be welcomed. Thank you.
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Re: Question about Linux and PTP over USB spec support

Marcus Meissner
On Wed, Jun 01, 2016 at 02:05:41AM -0700, Sean Hsu wrote:

> Hi guys:
> After reading your guys' post, I hope I can get some feedback here.
> My goal is to establish a connection between freescale iMX6qdl-sabresd Linux
> OS device and Windows PC using PTP(Picture Transfer Protocol) with USB
> cable. However, I do not even know how to start. I list my questions as
> below, please let me know if any of you knows the answer.
> 1. If any of you are familiar with freescale board, local.conf is the file
> that is used to add packages.
>     If what I need is to import some packages, what packages should I
> include? gphoto2, libptp? etc,. ?

Note that libgphoto2 is the initiator side, not the responder side.

For the intiator side the packages needed are usually gphoto2, libgphoto2,
and libusb at least. (libptp is not relevant.)

> 2. I know now PTP is the transport layer above the USB-IF physical layer.
> What should I do to enable the USB-IF and send PTP protocol? This involves a
> lot of self-coding. The best way is to find a library or packages that I can
> import to the freescale board and start using the PTP.

The userspace interface library used by libgphoto2 is usually libusb.

The kernel, whatever this board runs, needs to support userland USB.

> 3. If what I am trying to do is too complicated, I am not insist on doing
> it. However, I do want a linux and Windows connection with PTP or MTP using
> USB cable. Importing packages or libraries seem to be the best way to get
> started.
>
> Any ideas or concepts about what I mentioned above will be welcomed. Thank
> you.

If you want to create the device side, there are some responder implementations
in code.

Ciao, Marcus

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Re: Question about Linux and PTP over USB spec support

Sean Hsu
Hi Marcus:

Thanks for replying.

Note that libgphoto2 is the initiator side, not the responder side.

For the intiator side the packages needed are usually gphoto2, libgphoto2,
and libusb at least. (libptp is not relevant.)

===>does it mean that the freescale iMX6sabresd Linux-based OS board is the initiator side that initiates the connection by opening a session and the windows PC acts as a response side all the time in PTP protocol?
The Linux board is the device(usb-wise) and windows PC is the host(usb-wise) in PTP world?
Normally, if connecting a digital camera to a windows PC using USB cable by PTP protocol, which one is the initiator? the digital camera or the windows PC? who is the one sending the command who is the one responding?

I am trying to get the idea right. Thanks for replying.
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Re: Question about Linux and PTP over USB spec support

Marcus Meissner
On Thu, Jun 02, 2016 at 12:25:21AM -0700, Sean Hsu wrote:

> Hi Marcus:
>
> Thanks for replying.
>
> Note that libgphoto2 is the initiator side, not the responder side.
>
> For the intiator side the packages needed are usually gphoto2, libgphoto2,
> and libusb at least. (libptp is not relevant.)
>
> ===>does it mean that the freescale iMX6sabresd Linux-based OS board is the
> initiator side that initiates the connection by opening a session and the
> windows PC acts as a response side all the time in PTP protocol?
> The Linux board is the device(usb-wise) and windows PC is the host(usb-wise)
> in PTP world?
> Normally, if connecting a digital camera to a windows PC using USB cable by
> PTP protocol, which one is the initiator? the digital camera or the windows
> PC? who is the one sending the command who is the one responding?
>
> I am trying to get the idea right. Thanks for replying.

Your Linux board would simulate being the Device.

I had to look it up again, its confusing a bit.

In ISO 17540 / PTP standard speak:

        Device == Responder (your Linux board)
        Client == Initiator (your Windows System)

libgphoto2 provides a client/initiator implementation, but as you need
the responder side, it will not be much useful for you I am afraid.


There were some PTP/MTP responder source bases, although a quick google
search does not find them again :(

Ciao, Marcus

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Re: Question about Linux and PTP over USB spec support

Stefan Peter-4
Hi Marcus

Am 02.06.2016 um 10:55 schrieb Marcus Meissner:
>
> There were some PTP/MTP responder source bases, although a quick google
> search does not find them again :(

CHDK (http://chdk.wikia.com/wiki/CHDK) may have an implementation.

Regards

Stefan Peter



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Re: Question about Linux and PTP over USB spec support

Marcus Meissner
On Thu, Jun 02, 2016 at 11:36:22AM +0200, Stefan Peter wrote:
> Hi Marcus
>
> Am 02.06.2016 um 10:55 schrieb Marcus Meissner:
> >
> > There were some PTP/MTP responder source bases, although a quick google
> > search does not find them again :(
>
> CHDK (http://chdk.wikia.com/wiki/CHDK) may have an implementation.

They hook into the Canon PTP stack AFAIK.

Ciao, Marcus

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Re: Question about Linux and PTP over USB spec support

Sean Hsu
Hi Marcus:

I see what you meant. For libgphoto2 to work, the linux side should be the host side. However, I am connecting the board to the PC. The PC is the host, the board has to be the device. I will take a look at the link that you provided. If you have any further idea that might help me, please let me know. Thanks a lot.

BR
Sean Hsu
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Re: Question about Linux and PTP over USB spec support

Sean Hsu
Hi Marcus:

Sorry I couldn't find anything. I have couple of questions as below:

1. for PTP connection, what should I do to let Windows PC recognize the linux board as a device? For example, I connect PC to linux using mass storage, and after the USB connection, the linux side recognizes PC and PC recognizes the linux.

2. for PTP connection, do I need to set the command that enables the mass storage protocol? In other words, can PTP and mass storage coexist?

3. Is there any open source code example or packages for imx freescale board that implement the daemon side user code that calls PTP level API and PTP code calls USB level API? and most importantly, it has to be the responder side(PC as host, linux as device).

I really stuck here for a while now. If you can provide me anything that is more useful that I really get started with my process, I really appreciate. Thank you for replying.

BR
Sean Hsu
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Re: Question about Linux and PTP over USB spec support

Sean Hsu
Hi Marcus:

Any idea of what what I need to do? Any documents, even better sample codes about how to implement PTP side, USB side? Thanks for replying.

BR
Sean Hsu
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