On Friday 03 April 2009 12:12:30 Eduardo Valentin wrote: > On Thu, Apr 02, 2009 at 06:36:37PM +0200, ext Hans Verkuil wrote: > > On Thursday 02 April 2009 14:02:11 Eduardo Valentin wrote: > > > Hi Hans, > > > > > > On Thu, Apr 02, 2009 at 09:47:11AM +0200, ext Hans Verkuil wrote: > > > > On Wednesday 01 April 2009 11:43:28 Eduardo Valentin wrote: > > > > > Hello Mauro and v4l guys, > > > > > > > > > > This series contains a v4l2 radio driver which > > > > > adds support for Silabs si4713 devices. That is > > > > > a FM transmitter device. > > > > > > > > > > As you should know, v4l2 does not contain representation > > > > > of FM Transmitters (at least that I know). So this driver > > > > > was written highly based on FM receivers API, which can > > > > > cover most of basic functionality. However, as expected, > > > > > there are some properties which were not covered. > > > > > For those properties, sysfs nodes were added in order > > > > > to get user interactions. > > > > > > > > > > Comments are wellcome. > > > > > > > > Can you explain in reasonable detail the extra properties needed > > > > for a device like this? You will need to document that anyway :-) > > > > Rather than implementing a private API it would be much more > > > > interesting to turn this into a public V4L2 API that everyone can > > > > use. > > > > > > Yes, here is a little description of them: > > > > > > Pilot is an audible tone sent by the device. > > > > > > pilot_frequency - Configures the frequency of the stereo pilot tone. > > > pilot_deviation - Configures pilot tone frequency deviation level. > > > pilot_enabled - Enables or disables the pilot tone feature. > > > > > > The si4713 device is capable of applying audio compression to the > > > transmitted signal. > > > > > > acomp_enabled - Enables or disables the audio dynamic range control > > > feature. acomp_gain - Sets the gain for audio dynamic range control. > > > acomp_threshold - Sets the threshold level for audio dynamic range > > > control. acomp_attack_time - Sets the attack time for audio dynamic > > > range control. acomp_release_time - Sets the release time for audio > > > dynamic range control. > > > > > > Limiter setups audio deviation limiter feature. Once a over deviation > > > occurs, it is possible to adjust the front-end gain of the audio > > > input and always prevent over deviation. > > > > > > limiter_enabled - Enables or disables the limiter feature. > > > limiter_deviation - Configures audio frequency deviation level. > > > limiter_release_time - Sets the limiter release time. > > > > > > power_level - Sets the output power level for signal transmission. > > > > Hmm, there are two ways to implement these: either make a bunch of > > VIDIOC's for each of these categories, or use extended controls to set > > all these values. I'm hardly an expert on FM transmitters, but it all > > seems reasonable to me (i.e., not too specific for this chip). > > > > I am leaning towards extended controls, since that's so easy to extend > > if needed in the future. And I still intend to add sysfs support to > > controls in the future. On the other hand, it's a bit harder to use > > compared to normal VIDIOCs. > > Could you please explain more about extended controls vs. VIDIOC's? > Pointing drivers which uses one of those also would be worth. But yes, > looks like moving this properties to some sort of v4l2 control looks > better implementation. The spec explains it pretty well. The most up to date version of the spec is available here: http://www.xs4all.nl/~hverkuil/spec/v4l2.html. Basically the extended controls API is more flexible than the older VIDIOC_S/G_CTRL ioctls, allowing to set controls atomically (either all are applied or none) and allowing for a wider range of types, although currently that feature isn't used. It's used by uvcvideo and by MPEG encoders (e.g. cx18, ivtv and others). Using VIDIOCs is easier, but much harder to make future-proof. One disadvantage of using extended controls is that it is harder to implement in drivers, although I plan on creating a much better solution for that in the coming months. With the new v4l framework it should be possible to move much of the control handling into the framework and so simplifying the drivers. > > > RDS related > > > > > > rds_enabled - Enables or disables the RDS feature. > > > rds_ps_name - Sets the RDS ps name field for transmission. > > > rds_radio_text - Sets the RDS radio text for transmission. > > > rds_pi - Sets the RDS PI field for transmission. > > > rds_pty - Sets the RDS PTY field for transmission. > > > > So you set the fields and the RDS encoder will just start using them? > > Once you have rds_enabled set, yes, it will transmit them. > > > This too can be done with controls (needs some work, though, to support > > string controls). > > Yes, true. > > > > Region related > > > > > > Setting region will affect other region properties. > > > > > > region_bottom_frequency > > > region_channel_spacing > > > region_preemphasis > > > region_top_frequency > > > > I do not know enough about FM transmissions to judge this. Are these > > region properties something that is regulated by some standards > > commision? Do they also apply when you modulate this over a TV/radio > > cable system? Do you have some documentation or links that I can look > > at to learn more about this? > > > > > stereo_enabled - Enables or disables stereo mode. > > > > > > > How does one pass the audio and rds data to the driver? Note that > > > > for 2.6.31 we will finalize the V4L2 RDS decoder API (I recently > > > > posted an RFC for that, but I haven't had the time to implement the > > > > few changes needed). It would be nice if rds modulator support > > > > would be modeled after this demodulator API if possible. > > > > > > I see. This is good. I think the best way is to have a rds modulator > > > interface. This driver have implemented it as sys properties, as > > > described above. > > > > I don't think there is that much overlap, though. The similarities are > > probably limited to some flags. > > > > > > Does region information really belong in the driver? Perhaps this > > > > should be in a user-space library? (just a suggestion, I'm not sure > > > > at this stage). > > > > > > Ok. Yes, this could be better to implement in user land. However, > > > depending on region that would restrict other properties as well. > > > So, letting user space control that, would allow device operate in > > > wrong intervals for frequencies for instance. > > > > But if you are in region A and you setup the device for region B, then > > it's wrong as well, right? > > > > I also wonder if there are legal requirements that have to be followed > > here? > > Yes, the region thing is somehow bound to limits of specific area rules / > regulation. For instance, Europe frequencies limits are > .bottom_frequency = 8750, > .top_frequency = 10800, > > > BTW, maybe I'm making some confusion, but is there two different APIs for > radios? What is the difference in roles of things that goes into > drivers/media/radio and drivers/media/common/tuners? common/tuners is for the tuner devices (usually i2c). But in media/radio you find the actual v4l2 drivers. However, in a few cases this split wasn't done and there is no separate i2c driver created for the radio device: instead it is hardcoded into the v4l2 driver. This is bad and should be avoided for new drivers. We didn't always pay enough attention to this in the past. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by TANDBERG -- 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
