On Sun April 21 2013 12:09:51 Mauro Carvalho Chehab wrote: > Em 21-04-2013 06:34, Hans Verkuil escreveu: > > Hi Mauro, > > > > On Sat April 20 2013 19:51:11 Mauro Carvalho Chehab wrote: > >> This is a version 2 of the V4L2 API bits to support Software Digital > >> Radio (SDR). > > > > It looks pretty good to me. Just one question though: what is your rationale > > for choosing a new device name (/dev/sdrX) instead of using the existing > > /dev/radioX? > > > > I'm not saying I'm opposed to it, in fact I agree with it, but I think the > > reasons for it should be stated explicitly. > > Because a SDR radio is different than a normal radio device: > > A normal radio device is actually radio and hardware demod. As the demod > is in hardware, several things that are required for the demodulate the > signal (IF, bandwidth, sample rate, RF/IF filters, etc) are internal to > the device and aren't part of the API. > > SDR radio, on the other hand, requires that every control needed by the > tuner to be exposed on userspace, as userspace needs to adjust the > software decoder to match them. > > So, they're different. > > Btw, it is also possible that the same device to offer analog TV, > digital TV, hardware-decoded radio and SDR. One example of such devices > are cx88. The existing drivers supports already hardware demodulers, > but the device also allows to export the collected samples to userspace. > It is just a matter of programming the cx88 RISC code to do that. > > Internally, cx2388x has 2 10 bits ADC, one for baseband (composite inputs) > and another one for IF signal capable of working up to 35.44 MHz sampling > rate (on "8x FSC PAL" supported mode). It would be easy to export its > output to userspace. > > Btw, while seeking for more data about SDR this weekend, I discovered > one project doing exactly that: > > http://www.geocities.ws/how_chee/cx23881fc6.htm > > I did a very quick look at its source code. It is limited, as it works > only at a fixed sample rate of 27 MHz provides only 8 bits samples[1], and > I'm not sure if it allows using both ADCs. > > Yet, It shows that it is possible that a driver/subdrivers to offer > the 4 different types of devices: > - analog TV; > - digital TV; > - radio; > - SDR. > > So, IMO we should not abuse of /dev/radio for SDR. I agree. I just wanted to have it explicit :-) I also think we should provide and maintain a library doing the decoding for SDR that is part of v4l-utils. Otherwise you'll end up with a big userspace mess. And we want this checked by v4l2-compliance, and qv4l2 should be able to use the library so we have at least one application that can handle it. Regards, Hans > > Regards, > Mauro > > [1] The trick is to program the cx88 RISC to output data from the > samplers, instead of from the demods. We do that already for the > audio standard detection. > > I've no idea if cx88 has any upper DMA maximum bandwidth. If it has, > that might be the reason to limit to 27MHz, 8 bits, but I suspect > that it was done that way just because it was easier. > > Btw, I'm almost sure that other Conexant designs can also offer > similar interfaces. > > > > > > Regards, > > > > Hans > > > >> > >> > >> The changes from version 1 are: > >> - fix compilation; > >> - add a new capture type for SDR (V4L2_BUF_TYPE_SDR_CAPTURE), > >> with the corresponding documentation; > >> - remove legacy V4L1 buffer types from videobuf2.h. > >> > >> With regards to VIDIOC_S_TUNER, what's currently defined there is > >> that, in contrary to what a radio device does, this ioctl would > >> set the input. > >> > >> This patch adds the very basic stuff for SDR: > >> > >> - a separate devnode; > >> - an VIDIOC_QUERYCAP caps for SDR; > >> - a fourcc group for SDR; > >> - a few DocBook bits. > >> > >> What's missing: > >> - SDR specific controls; > >> - Sample rate config; > >> ... > >> > >> As discussing DocBook changes inside the patch is hard, I'm adding here > >> the DocBook formatted changes. > >> > >> The DocBook changes add the following bits: > >> > >> At Chapter 1. Common API Elements, it adds: > >> > >> <text> > >> Software Digital Radio (SDR) Tuners and Modulators > >> ================================================== > >> > >> Those devices are special types of Radio devices that don't have any > >> analog demodulator. Instead, it samples the radio IF or baseband and > >> sends the samples for userspace to demodulate. > >> > >> Tuners > >> ====== > >> > >> SDR receivers can have one or more tuners sampling RF signals. Each > >> tuner is associated with one or more inputs, depending on the number of > >> RF connectors on the tuner. The type field of the respective struct > >> v4l2_input returned by the VIDIOC_ENUMINPUT ioctl is set to > >> V4L2_INPUT_TYPE_TUNER and its tuner field contains the index number of > >> the tuner input. > >> > >> To query and change tuner properties applications use the VIDIOC_G_TUNER > >> and VIDIOC_S_TUNER ioctl, respectively. The struct v4l2_tuner returned > >> by VIDIOC_G_TUNER also contains signal status information applicable > >> when the tuner of the current SDR input is queried. In order to change > >> the SDR input, VIDIOC_S_TUNER with a new SDR index should be called. > >> Drivers must support both ioctls and set the V4L2_CAP_SDR and > >> V4L2_CAP_TUNER flags in the struct v4l2_capability returned by the > >> VIDIOC_QUERYCAP ioctl. > >> > >> Modulators > >> ========== > >> > >> To be defined. > >> </text> > >> > >> At the end of Chapter 2. Image Formats, it adds: > >> > >> <text> > >> SDR format struture > >> =================== > >> > >> Table 2.4. struct v4l2_sdr_format > >> ================================= > >> > >> __u32 sampleformat The format of the samples used by the SDR device. > >> This is a little endian four character code. > >> > >> Table 2.5. SDR formats > >> ====================== > >> > >> V4L2_SDR_FMT_I8Q8 Samples are given by a sequence of 8 bits in-phase(I) > >> and 8 bits quadrature (Q) samples taken from a > >> signal(t) represented by the following expression: > >> signal(t) = I * cos(2π fc t) - Q * sin(2π fc t) > >> </text> > >> > >> Of course, other formats will be needed at Table 2.5, as SDR could also > >> be taken baseband samples, being, for example, a simple sequence of > >> equally time-spaced digitalized samples of the signal in time. > >> SDR samples could also use other resolutions, use a non-linear > >> (A-law, u-law) ADC, or even compress the samples (with ADPCM, for > >> example). So, this table will grow as newer devices get added, and an > >> userspace library may be required to convert them into some common > >> format. > >> > >> At "Chapter 4. Interfaces", it adds the following text: > >> > >> <text> > >> Software Digital Radio(SDR) Interface > >> ===================================== > >> > >> This interface is intended for Software Digital Radio (SDR) receivers > >> and transmitters. > >> > >> Conventionally V4L2 SDR devices are accessed through character device > >> special files named /dev/sdr0 to/dev/radio255 and uses a dynamically > >> allocated major/minor number. > >> > >> Querying Capabilities > >> ===================== > >> > >> Devices supporting the radio interface set the V4L2_CAP_SDR and > >> V4L2_CAP_TUNER or V4L2_CAP_MODULATOR flag in the capabilities field of > >> struct v4l2_capability returned by the VIDIOC_QUERYCAP ioctl. Other > >> combinations of capability flags are reserved for future extensions. > >> > >> Supplemental Functions > >> ====================== > >> > >> SDR receivers should support tuner ioctls. > >> > >> SDR transmitter ioctl's will be defined in the future. > >> > >> SDR devices should also support one or more of the following I/O ioctls: > >> read or write, memory mapped IO, user memory IO and/or DMA buffers. > >> > >> SDR devices can also support controls ioctls. > >> > >> The SDR Input/Output are A/D or D/A samples taken from a modulated > >> signal, and can eventually be packed by the hardware. They are generally > >> encoded using cartesian in-phase/quadrature (I/Q) samples, to make > >> demodulation easier. The format of the samples should be according with > >> SDR format. > >> </text> > >> > >> Note: "SDR format" on the last paragraph is an hyperlink to > >> Chapter 2. Image Formats. > >> > >> At "Appendix A. Function Reference - ioctl VIDIOC_QUERYCAP", it adds: > >> > >> <text> > >> Table A.93. Device Capabilities Flags > >> ... > >> V4L2_CAP_SDR 0x00100000 The device is a Software Digital Radio. > >> For more information about SDR programming > >> see the section called “Software Digital > >> Radio (SDR) Tuners and Modulators�. > >> </text> > >> > >> Mauro Carvalho Chehab (3): > >> [media] Add SDR at V4L2 API > >> videodev2.h: Remove the unused old V4L1 buffer types > >> [media] V4L2 api: Add a buffer capture type for SDR > >> > >> Documentation/DocBook/media/v4l/common.xml | 35 ++++++++++++++++++ > >> Documentation/DocBook/media/v4l/dev-capture.xml | 26 ++++++++------ > >> Documentation/DocBook/media/v4l/io.xml | 6 ++++ > >> Documentation/DocBook/media/v4l/pixfmt.xml | 41 ++++++++++++++++++++++ > >> Documentation/DocBook/media/v4l/v4l2.xml | 1 + > >> .../DocBook/media/v4l/vidioc-querycap.xml | 7 ++++ > >> drivers/media/v4l2-core/v4l2-dev.c | 3 ++ > >> drivers/media/v4l2-core/v4l2-ioctl.c | 32 +++++++++++++++++ > >> include/media/v4l2-dev.h | 3 +- > >> include/media/v4l2-ioctl.h | 8 +++++ > >> include/uapi/linux/videodev2.h | 33 +++++++---------- > >> 11 files changed, 163 insertions(+), 32 deletions(-) > >> > >> > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-media" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
