Em Thu, 21 Nov 2013 19:22:51 +0100
Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
> On 11/21/2013 06:49 PM, Mauro Carvalho Chehab wrote:
> > Em Thu, 21 Nov 2013 19:05:05 +0200
> > Antti Palosaari <crope@xxxxxx> escreveu:
> >
> >> Hello
> >> I am adding new property for sampling rate that is ideally the only
> >> obligatory parameter required by SDR. It is value that could be only
> >> positive and bigger the better, lets say unsigned 64 bit is quite ideal.
> >> That value sets maximum radio frequency possible to receive (ideal SDR).
> >>
> >> Valid values are not always in some single range from X to Y, there
> >> could be some multiple value ranges.
> >>
> >> For example possible values: 1000-2000, 23459, 900001-2800000
> >>
> >> Reading possible values from device could be nice, but not necessary.
> >> Reading current value is more important.
> >>
> >> Here is what I though earlier as a requirements:
> >>
> >> sampling rate
> >> * values: 1 - infinity (unit: Hz, samples per second)
> >> currently 500 MHz is more than enough
> >> * operations
> >> GET, inquire what HW supports
> >> GET, get current value
> >> SET, set desired value
> >>
> >>
> >> I am not sure what is best way to implement that kind of thing.
> >> IOCTL like frequency
> >> V4L2 Control?
> >> put it into stream format request?
> >>
> >> Sampling rate is actually frequency of ADC. As there devices has almost
> >> always tuner too (practical SDR) there is need for tuner frequency too.
> >> As tuner is still own entity, is it possible to use same frequency
> >> parameter for both ADC and RF tuner in same device?
> >
> > Well, a SDR capture device will always have ADC and RF tuner.
> >
> > A SDR output device will always have a DAC and a RF transmitter.
> >
> > On both cases, the sampling rate and the sampling format are mandatory
> > arguments.
> >
> > In any case, the V4L2 API has already support for setting the mandatory
> > parameters of the expected stream, at struct v4l2_format.
> >
> > So, it makes sense do do:
> >
> > struct v4l2_format {
> > __u32 type;
> > union {
> > struct v4l2_pix_format pix; /* V4L2_BUF_TYPE_VIDEO_CAPTURE */
> > struct v4l2_pix_format_mplane pix_mp; /* V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE */
> > struct v4l2_window win; /* V4L2_BUF_TYPE_VIDEO_OVERLAY */
> > struct v4l2_vbi_format vbi; /* V4L2_BUF_TYPE_VBI_CAPTURE */
> > struct v4l2_sliced_vbi_format sliced; /* V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */
> > + struct v4l2_sdr_format sdr; /* V4L2_BUF_TYPE_SDR_CAPTURE */
> > __u8 raw_data[200]; /* user-defined */
> > } fmt;
> > };
> >
> > And add the mandatory parameters for SDR inside its own structure, e. g.
> > struct v4l2_sdr_format. Of course, the meta-data provided by a SDR device
> > is different than the one for video or vbi, so you'll need to add a new
> > streaming type for SDR anyway.
> >
> > Btw, that's what I proposed here:
> >
> > http://git.linuxtv.org/mchehab/experimental.git/blob/refs/heads/sdr:/include/uapi/linux/videodev2.h
> >
> > With regards to the sampling rate range, my proposal there were to add a min/max
> > value for it, to be used by VIDIOC_G_FMT, as proposed on:
> > http://git.linuxtv.org/mchehab/experimental.git/commitdiff/c3a73f84f038f043aeda5d5bfccc6fea66291451
> >
> > So, the v4l2_sdr_format should be like:
> >
> > +struct v4l2_sdr_format {
> > + __u32 sampleformat;
> > + __u32 sample_rate; /* in Hz */
> > + __u32 min_sample_rate; /* in Hz */
> > + __u32 max_sample_rate; /* in Hz */
> > +
> > +} __attribute__ ((packed));
> >
> > Where sampleformat would be something similar to FOURCC, defining the
> > size of each sample, its format, and if the sampling is in quadradure,
> > if they're plain PCM samples, or something more complex, like DPCM, RLE,
> > etc.
> >
> > In the specific case of enumerating the sampling rate range, if the
> > sampling rate can have multiple ranges, then maybe we'll need to do
> > something more complex like what was done on VIDIOC_ENUM_FRAMESIZES.
>
> Could this ioctl be adapted for this:
>
> http://hverkuil.home.xs4all.nl/spec/media.html#vidioc-enum-freq-bands
I don't think so. Btw, it makes sense to have different frequency bands
for SDR too.
> BTW, can the sample rate change while streaming? Typically things you set
> through S_FMT can not be changed while streaming.
I don't think you can. If the sampling rate changes, you need to know exactly
on what sample the bit rate changed, or otherwise you can't decode the
samples.
In other words, you need to first stream off, then change the sampling rate,
then do a stream on.
Cheers,
Mauro
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