Re: [Xenomai-core] rt-video interface
Em Domingo 26 Março 2006 06:49, Jan Kiszka escreveu: >... >Maybe derived a subset from the full V4L2 API is the way to go. But >let's wait if you discover other interface designs. Actually, my priorities changed again... I'll need to finish (start actually) an application using the camera in a hard real-time context for writing another article for RTSS (http://www.rtss.org) that will happen in Brazil this year. Hope to see some of you here if my article is approved. Then I will come back to my interface designs research... >... >> This method also requires poll and select to be implemented in V4L2. We >> should discuss how to deal with it if we stick with the V4L2 variant idea. > >Hmm, what file descriptors have to be monitored in parallel so that >poll/select is required? I didn't really understand why should poll/select be required, but the author says it is too important to be optional... We should ask him why ;) Anyway, there are more efficient ways for monitoring a buffer state and wait for events in RTDM. I don't think we should use poll/select anyway... >... >> Which vision applications do you have in mind? > >So far "only" a subset of your scenario: One of my colleagues needs to >synchronise frame timestamps with timestamps of other input, from range >sensors e.g. The actually processing is not (yet?) hard RT, but the >input synchronisation is essential. I think that the timestamp provided by the interface is enough, don't you think? Best Regards, Rodrigo. ___ Yahoo! doce lar. Faça do Yahoo! sua homepage. http://br.yahoo.com/homepageset.html ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] rt-video interface
Rodrigo Rosenfeld Rosas wrote:
> Em Segunda 20 Março 2006 21:24, Jan Kiszka escreveu:
>> ...
>> Does your time allow to list the minimal generic services a RTDM video
>> capturing driver has to provide in a similar fashion like the serial or
>> the CAN profile? If it's mostly about copying existing Linux API specs,
>> feel free to just reference them. But the differences should certainly
>> fill up a RT-video (or so) profile, and that would be great!
>
> If we're going to try to be as near as possible of the V4L2 API draft, the
> minimal generic services is a lot to implement.
>
> Actually, I don't know if implementing a V4L2 variant would be a good idea...
> Maybe there are designs better suited to real-time applications. I need time
> to investigate it more. My advisor asked me for. It's becoming really hard to
> finish my master Thesis until June 15... :(
Maybe derived a subset from the full V4L2 API is the way to go. But
let's wait if you discover other interface designs.
>
> Basically I would need to have it clearer the most common use cases in real
> situations... From the moment, here is my design (from a user point of view
> of one kind of application): I'm using images to estimate speed of a robot
> and identifying objects. I need the timestamps between both images and all
> processes must be deterministic. I process the images and do the
> calculations.
>
> For avoid copying, I'm using the mmap facility. I process the image in the
> same memory region when possible for avoidind the need of allocating more
> memory. When using a NTSC camera, we have 60Hz frames, being 30 odds and 30
> evens in a second. It means that a full frame (odd+even) would take about
> 33ms to complete. It is common, though, to use only half a frame in
> processing not only because it is faster to acquire (17ms) but it is also
> faster to process and acceptable in most cases. So, instead of 640x480 frames
> we would process 640x240 frames. If the proportion is important, the user can
> do something like:
>
> for (w1=0,w=0; w1<640; w1+=2, w++)
> for(h=0; h<240; h++)
> {
>process_pixel(w,h);
> }
>
> If all the processing can me made in 17ms, we could process the odd field
> when
> acquiring the even and vice-versa. Otherwise, we could have a buffer with the
> latest acquires so that we wouldn't need to wait until a frame is completed.
>
> In summary, my control loop would be something like:
>
> task_acquire
> {
> new_image=acquire_image();
> speed=get_speed(new_image,old_image);
> old_image = new_image;
> }
>
> task_do_pid_control
> {
> drive_motors(speed, desired_speed);
> }
>
> Well, that is a use case and I can get this behaviour with the V4L2 API,
> although I don't know if it is the best suited API. Let me introduce the V4L2
> API and then (in other messages) we can discuss others approaches.
>
> There are some interfaces available in V4L2: capture, overlay and output.
> I'll
> discuss only capture here that I think it is the most relevant for
> rt-applications.
>
> There are four IO modes: read/write, streaming I/O (memory mapping or user
> pointer) and asyncronous I/O.
>
> The read/write mode is the simplest but also the less efficient, since it
> copies the buffer content to the user. It works like it is expected to. On
> V4L2 API it requires the poll and select implementation but we could adapt
> them to a simpler and more efficient way.
>
> The user pointer approach has no sense for PCI framegrabbers on x86, since
> these boards need a physical contiguous memory region for doing DMA. This
> method consists on the user allocating the memory on userspace and passing
> the pointers to the drivers.
>
> The asyncronous I/O is not defined yer, so there are three and not four I/O
> modes.
>
> The third is the most useful for real-time applications and is what I'm
> currently using: streaming by memory mapping.
> See http://www.linuxtv.org/downloads/video4linux/API/V4L2_API/spec/x3303.htm
>
> In short, the user request a number of buffers in VIDIOC_REQBUFS ioctl and
> the
> driver allocate or reserve them and return the number of actual allocated
> buffers.
>
> There is another ioctl (VIDIOC_QUERYBUF) for querying each buffer. Along with
> other information, the user gets a memory offset to be used in a mmap call.
> Then the buffers will be queued in a input buffer with the VIDIOC_QBUF ioctl.
> When the VIDIOC_STREAMON ioctl is called, the board begins capturing in FIFO
> order of the input buffer and as the acquires are done the buffers are moved
> to an output buffer also in FIFO order. The user dequeue a buffer from the
> output buffer with the VIDIOC_DQBUF ioctl. When the user has finished using
> the result of that buffer (s)he will enqueues it again. When stop processing,
> a VIDIOC_STREAMOFF ioctl call is made and cleans all buffers besides stopping
> capture.
This sounds best applicable for hard RT indeed.
>
> This
Re: [Xenomai-core] rt-video interface
Em Segunda 20 Março 2006 21:24, Jan Kiszka escreveu:
>...
>Does your time allow to list the minimal generic services a RTDM video
>capturing driver has to provide in a similar fashion like the serial or
>the CAN profile? If it's mostly about copying existing Linux API specs,
>feel free to just reference them. But the differences should certainly
>fill up a RT-video (or so) profile, and that would be great!
If we're going to try to be as near as possible of the V4L2 API draft, the
minimal generic services is a lot to implement.
Actually, I don't know if implementing a V4L2 variant would be a good idea...
Maybe there are designs better suited to real-time applications. I need time
to investigate it more. My advisor asked me for. It's becoming really hard to
finish my master Thesis until June 15... :(
Basically I would need to have it clearer the most common use cases in real
situations... From the moment, here is my design (from a user point of view
of one kind of application): I'm using images to estimate speed of a robot
and identifying objects. I need the timestamps between both images and all
processes must be deterministic. I process the images and do the
calculations.
For avoid copying, I'm using the mmap facility. I process the image in the
same memory region when possible for avoidind the need of allocating more
memory. When using a NTSC camera, we have 60Hz frames, being 30 odds and 30
evens in a second. It means that a full frame (odd+even) would take about
33ms to complete. It is common, though, to use only half a frame in
processing not only because it is faster to acquire (17ms) but it is also
faster to process and acceptable in most cases. So, instead of 640x480 frames
we would process 640x240 frames. If the proportion is important, the user can
do something like:
for (w1=0,w=0; w1<640; w1+=2, w++)
for(h=0; h<240; h++)
{
process_pixel(w,h);
}
If all the processing can me made in 17ms, we could process the odd field when
acquiring the even and vice-versa. Otherwise, we could have a buffer with the
latest acquires so that we wouldn't need to wait until a frame is completed.
In summary, my control loop would be something like:
task_acquire
{
new_image=acquire_image();
speed=get_speed(new_image,old_image);
old_image = new_image;
}
task_do_pid_control
{
drive_motors(speed, desired_speed);
}
Well, that is a use case and I can get this behaviour with the V4L2 API,
although I don't know if it is the best suited API. Let me introduce the V4L2
API and then (in other messages) we can discuss others approaches.
There are some interfaces available in V4L2: capture, overlay and output. I'll
discuss only capture here that I think it is the most relevant for
rt-applications.
There are four IO modes: read/write, streaming I/O (memory mapping or user
pointer) and asyncronous I/O.
The read/write mode is the simplest but also the less efficient, since it
copies the buffer content to the user. It works like it is expected to. On
V4L2 API it requires the poll and select implementation but we could adapt
them to a simpler and more efficient way.
The user pointer approach has no sense for PCI framegrabbers on x86, since
these boards need a physical contiguous memory region for doing DMA. This
method consists on the user allocating the memory on userspace and passing
the pointers to the drivers.
The asyncronous I/O is not defined yer, so there are three and not four I/O
modes.
The third is the most useful for real-time applications and is what I'm
currently using: streaming by memory mapping.
See http://www.linuxtv.org/downloads/video4linux/API/V4L2_API/spec/x3303.htm
In short, the user request a number of buffers in VIDIOC_REQBUFS ioctl and the
driver allocate or reserve them and return the number of actual allocated
buffers.
There is another ioctl (VIDIOC_QUERYBUF) for querying each buffer. Along with
other information, the user gets a memory offset to be used in a mmap call.
Then the buffers will be queued in a input buffer with the VIDIOC_QBUF ioctl.
When the VIDIOC_STREAMON ioctl is called, the board begins capturing in FIFO
order of the input buffer and as the acquires are done the buffers are moved
to an output buffer also in FIFO order. The user dequeue a buffer from the
output buffer with the VIDIOC_DQBUF ioctl. When the user has finished using
the result of that buffer (s)he will enqueues it again. When stop processing,
a VIDIOC_STREAMOFF ioctl call is made and cleans all buffers besides stopping
capture.
This method also requires poll and select to be implemented in V4L2. We should
discuss how to deal with it if we stick with the V4L2 variant idea.
I would like to understand what would be other possible usages of real-time
vision before I could propose another approach so we can discuss what would
be better for us.
Besides the API issue, we should think also on the API implementation. I think
we should
Re: [Xenomai-core] rt-video interface
Em Segunda 20 Março 2006 21:24, Jan Kiszka escreveu: >... >You may want to have a look at this thread regarding poll/select and RT: >http://www.mail-archive.com/rtnet-users%40lists.sourceforge.net/msg00968.htm I tried to. Not found. But I didn't give up so quicky. It was missing the final 'l': http://www.mail-archive.com/rtnet-users%40lists.sourceforge.net/msg00968.html >Do video capturing applications tend to have to observe multiple >channels asynchronously via a single thread? If so, my statement about >how often poll/select is actually required in RT-applications may have >to be reconsidered. Actually, I don't see any reasonable reason for using select/poll in rt applications. But, while trying to keep the API similar to V4L2, I would implement them by IOCTL and think it is OK, since it was already done for MMAP/MUNMAP. I don't think it worths writing the poll/select rt like functions... What could be discussed here is if it will be required or not to have those calls needed when using streaming (most designs will use streaming). I don't think it should be required as it is on V4L2, but could be implemented optionally, as IOCTL calls. But I would need to investigate more this topic. I'll do it tomorrow... I'm the last man in the lab and they are calling me out for closing the lab... >... >Does your time allow to list the minimal generic services a RTDM video >capturing driver has to provide in a similar fashion like the serial or >the CAN profile? If it's mostly about copying existing Linux API specs, >feel free to just reference them. But the differences should certainly >fill up a RT-video (or so) profile, and that would be great! I'll think about it and will answer tomorrow. Regards, Rodrigo ___ Yahoo! doce lar. Faça do Yahoo! sua homepage. http://br.yahoo.com/homepageset.html ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
Re: [Xenomai-core] rt-video interface
Rodrigo Rosenfeld Rosas wrote: > Hi Jan and others interested. > > I've finally got my driver in a usable condition. It lacks a lot of > functionalities yet, but it aplies to my needs. > > I would like to propose a real-time video interface for using with RTDM. > > For making it simple to port Linux applications to Xenomai, I tried to make > it > as close as possible to Video for Linux 2 API. I didn't see any serious > problem regarding its use on real-time environments in the specification. So, > the changes I think that would be necessary are: > > o Change open/fopen to rtdm_dev_open > o Implement MMAP/MUNMAP as an IOCTL (while it can not be done in a rt-context > in the mean time, nor should be necessary) > o Implement also as IOCTLs: select and poll (I didn't implement them on my > driver because I didn't need them, but it should be necessary accordling to > specs) You may want to have a look at this thread regarding poll/select and RT: http://www.mail-archive.com/rtnet-users%40lists.sourceforge.net/msg00968.htm Do video capturing applications tend to have to observe multiple channels asynchronously via a single thread? If so, my statement about how often poll/select is actually required in RT-applications may have to be reconsidered. > o Change all timeval structs to uint64_t or some typedef to it for making it > easier to store the timestamps (we use rtdm_clock_read() instead of > gettimeofday()) > > I can't remember of another issue now. I think these changes would be enough. > > Any ideas? Does your time allow to list the minimal generic services a RTDM video capturing driver has to provide in a similar fashion like the serial or the CAN profile? If it's mostly about copying existing Linux API specs, feel free to just reference them. But the differences should certainly fill up a RT-video (or so) profile, and that would be great! Jan signature.asc Description: OpenPGP digital signature ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
[Xenomai-core] rt-video interface
Hi Jan and others interested. I've finally got my driver in a usable condition. It lacks a lot of functionalities yet, but it aplies to my needs. I would like to propose a real-time video interface for using with RTDM. For making it simple to port Linux applications to Xenomai, I tried to make it as close as possible to Video for Linux 2 API. I didn't see any serious problem regarding its use on real-time environments in the specification. So, the changes I think that would be necessary are: o Change open/fopen to rtdm_dev_open o Implement MMAP/MUNMAP as an IOCTL (while it can not be done in a rt-context in the mean time, nor should be necessary) o Implement also as IOCTLs: select and poll (I didn't implement them on my driver because I didn't need them, but it should be necessary accordling to specs) o Change all timeval structs to uint64_t or some typedef to it for making it easier to store the timestamps (we use rtdm_clock_read() instead of gettimeofday()) I can't remember of another issue now. I think these changes would be enough. Any ideas? Rodrigo. ___ Yahoo! Acesso Grátis - Internet rápida e grátis. Instale o discador agora! http://br.acesso.yahoo.com ___ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
