Programming N800 FM radio receiver - Revision history

amigadave: cut section headings

2010-09-14T09:33:32Z

cut section headings

← Older revision		Revision as of 09:33, 14 September 2010
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-	~~== How to control the FM tuner chip in the N800 ==~~
-
	The [[Nokia N800\|N800]] internet tablet features a tea5761 FM tuner chip for listening		The [[Nokia N800\|N800]] internet tablet features a tea5761 FM tuner chip for listening
	to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the Maemo kernel source code.		to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the Maemo kernel source code.
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	The driver implements the V4L2 radio interface and is thus controlled like a V4L2 device.		The driver implements the V4L2 radio interface and is thus controlled like a V4L2 device.

-	=== How to do it in Python ===	+	== How to do it in Python ==

	By using Python's <code>ioctl</code> function, you can directly talk to the driver, so there is no need for wrapping some C library.		By using Python's <code>ioctl</code> function, you can directly talk to the driver, so there is no need for wrapping some C library.

-	==== Prerequisites ====	+	=== Prerequisites ===

	Let's first import the required modules:		Let's first import the required modules:
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	</source>		</source>

-	==== Opening the device ====	+	=== Opening the device ===

	You gain access to the radio driver by opening the <code>/dev/radio</code> device. Since you need a system FD instead of a native Python FD, we use <code>os.open</code> instead of the built-in function <code>open</code>:		You gain access to the radio driver by opening the <code>/dev/radio</code> device. Since you need a system FD instead of a native Python FD, we use <code>os.open</code> instead of the built-in function <code>open</code>:
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	If there's no tuner chip available (for example, if you run this code on the [[Nokia 770\|770]] or the [[Nokia N810\|N810]]), this line will throw an <code>OSError</code>. Don't forget to catch it.		If there's no tuner chip available (for example, if you run this code on the [[Nokia 770\|770]] or the [[Nokia N810\|N810]]), this line will throw an <code>OSError</code>. Don't forget to catch it.

-	==== Retrieving information about the FM tuner ====	+	=== Retrieving information about the FM tuner ===

	Now it's time to talk to the FM tuner. We do this by placing an <code>ioctl</code>'' call on the device. <code>ioctl</code> calls consist of a number (those we have defined above), and some argument. The argument is a pointer for passing a C structure to the driver. The driver may read from this structure or write into it.		Now it's time to talk to the FM tuner. We do this by placing an <code>ioctl</code>'' call on the device. <code>ioctl</code> calls consist of a number (those we have defined above), and some argument. The argument is a pointer for passing a C structure to the driver. The driver may read from this structure or write into it.
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	We should save the <code>tuner_index</code> and <code>tuner_name</code> for later, because this is how we address that particular tuner.		We should save the <code>tuner_index</code> and <code>tuner_name</code> for later, because this is how we address that particular tuner.

-	==== Setting the frequency ====	+	=== Setting the frequency ===

	Next, we are going to tune into a radio station. For this, we have to set a frequency on the tuner. This is done by the V4L2 <code>_VIDIOC_G_FREQUENCY</code> <code>ioctl</code> invokation.		Next, we are going to tune into a radio station. For this, we have to set a frequency on the tuner. This is done by the V4L2 <code>_VIDIOC_G_FREQUENCY</code> <code>ioctl</code> invokation.
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	</source>		</source>

-	==== Unmuting the tuner and setting the volume ====	+	=== Unmuting the tuner and setting the volume ===

	You still do not hear anything from the radio. This is because the tuner is muted and its volume is set to 0. Let's change this:		You still do not hear anything from the radio. This is because the tuner is muted and its volume is set to 0. Let's change this:
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	Now you can listen to the radio.		Now you can listen to the radio.

-	==== Cleaning up ====	+	=== Cleaning up ===

	When you have finished listening to the radio, you should clean up and		When you have finished listening to the radio, you should clean up and
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	</source>		</source>

-	=== Code ready for use ===	+	== Code ready for use ==

	There is a pure Python module available for controlling the FM tuner. It is based on the information here. You can get it from [http://pyfmradio.garage.maemo.org the PyFMRadio project page].		There is a pure Python module available for controlling the FM tuner. It is based on the information here. You can get it from [http://pyfmradio.garage.maemo.org the PyFMRadio project page].

amigadave: Programming FM radio moved to Programming N800 FM radio receiver: device-specific

2010-09-14T09:31:56Z

Programming FM radio moved to Programming N800 FM radio receiver: device-specific

← Older revision

Revision as of 09:31, 14 September 2010

amigadave: wikify slightly, use , add Category:Python

2010-09-14T09:28:56Z

wikify slightly, use <source>, add Category:Python

Show changes

amigadave: /* Introduction */ link to Nokia N800

2010-04-26T09:19:07Z

Introduction: link to Nokia N800

← Older revision		Revision as of 09:19, 26 April 2010
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	== Introduction ==		== Introduction ==

-	The N800 internet tablet features a tea5761 FM tuner chip for listening	+	The [[Nokia N800\|N800]] internet tablet features a tea5761 FM tuner chip for listening
	to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the Maemo kernel source code.		to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the Maemo kernel source code.

amigadave: fix category

2010-02-04T13:14:40Z

fix category

← Older revision		Revision as of 13:14, 4 February 2010
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	[[Category:Development]]		[[Category:Development]]
-	[[Category:~~N800~~]]	+	[[Category:N8x0]]
	[[Category:Midgard wiki]]		[[Category:Midgard wiki]]

amigadave: add N800 category

2010-02-04T13:14:14Z

add N800 category

← Older revision		Revision as of 13:14, 4 February 2010
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	[[Category:Development]]		[[Category:Development]]
		+	[[Category:N800]]
	[[Category:Midgard wiki]]		[[Category:Midgard wiki]]

dneary: /* Introduction */

2008-12-03T21:14:00Z

Introduction

← Older revision		Revision as of 21:14, 3 December 2008
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-
	{{Midgard article}}		{{Midgard article}}

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	The N800 internet tablet features a tea5761 FM tuner chip for listening		The N800 internet tablet features a tea5761 FM tuner chip for listening
-	to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the ~~maemo~~ kernel source code.	+	to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the Maemo kernel source code.

	The driver implements the V4L2 radio interface and is thus controlled like a V4L2 device.		The driver implements the V4L2 radio interface and is thus controlled like a V4L2 device.
-

	== How to do it in Python ==		== How to do it in Python ==

dneary: Initial import of FM Radio programming

2008-06-11T09:53:36Z

Initial import of FM Radio programming

New page

{{Midgard article}}

= How to control the FM tuner chip in the N800 =

== Introduction ==

The N800 internet tablet features a tea5761 FM tuner chip for listening
to FM radio. The kernel driver for this chip was written by Nokia and is GPL'd open source. You can look at it by downloading the maemo kernel source code.

The driver implements the V4L2 radio interface and is thus controlled like a V4L2 device.

== How to do it in Python ==

By using Pythons `ioctl` function, you can directly talk to the driver, so there's no need for wrapping some C library.

=== Prerequisites ===

Let's first import the required modules:

import os # for opening the device files
import struct # for packing and unpacking C structs
from fcntl import ioctl # for invoking ioctl calls on the device files

Since we are going to talk to kernel drivers, we have to use weird numbers. C users would just include the appropriate Linux kernel header files, but Python users have to do it by hand. So let's make some defines for kernel level ioctl stuff:

<pre>
# kernel definitions for ioctl commands
_IOC_NRBITS = 8
_IOC_TYPEBITS = 8
_IOC_SIZEBITS = 14
_IOC_DIRBITS = 2

_IOC_NRSHIFT = 0
_IOC_TYPESHIFT = _IOC_NRSHIFT + _IOC_NRBITS
_IOC_SIZESHIFT = _IOC_TYPESHIFT + _IOC_TYPEBITS
_IOC_DIRSHIFT = _IOC_SIZESHIFT + _IOC_SIZEBITS

_IOC_WRITE = 1
_IOC_READ = 2

_IOC = lambda d,t,nr,size: (d << _IOC_DIRSHIFT) | (ord(t) << _IOC_TYPESHIFT) | \
(nr << _IOC_NRSHIFT) | (size << _IOC_SIZESHIFT)
_IOW = lambda t,nr,size: _IOC(_IOC_WRITE, t, nr, size)
_IOR = lambda t,nr,size: _IOC(_IOC_READ, t, nr, size)
_IOWR = lambda t,nr,size: _IOC(_IOC_READ | _IOC_WRITE, t, nr, size)
</pre>

The functions ''_IOW'', ''_IOR'', and ''_IOWR'' (macros in C) are used for write-access, read-access, and read-write-access, respectively. They basically just take some input values and compute a number which can be sent to the device driver. You can think of the number as the signature of the function which you want to call on the driver.

Now we can generate those weird numbers for the V4L2 functions we are
going to invoke on the driver:

<pre>
# V4L2 stuff for accessing the tuner driver
_VIDIOC_G_TUNER = _IOWR('V', 29, 84)
_VIDIOC_G_AUDIO = _IOR ('V', 33, 52)
_VIDIOC_S_AUDIO = _IOW ('V', 34, 52)
_VIDIOC_G_FREQUENCY = _IOWR('V', 56, 44)
_VIDIOC_S_FREQUENCY = _IOW ('V', 57, 44)
_VIDIOC_G_CTRL = _IOWR('V', 27, 8)
_VIDIOC_S_CTRL = _IOWR('V', 28, 8)

# user-class control IDs defined by V4L2
_V4L2_CTRL_CLASS_USER = 0x00980000
_V4L2_CID_BASE = _V4L2_CTRL_CLASS_USER | 0x900
_V4L2_CID_AUDIO_MUTE = _V4L2_CID_BASE + 9
</pre>

And last, let's define some numbers for working with the mixer device:

<pre>
# mixer control constants
_SOUND_MIXER_FMRADIO = 0x06
_SOUND_MIXER_READ = 0x80044D00
_SOUND_MIXER_WRITE = 0xC0044D00

</pre>

=== Opening the device ===

You gain access to the radio driver by opening the ''/dev/radio''
device. Since you need a system FD instead of a native Python FD, we use
''os.open'' instead of the built-in function ''open'':

radio_fd = os.open("/dev/radio", os.O_RDONLY)

If there's no tuner chip available (e.g. if you run this code on the 770 or the N810), this line will throw an `OSError`. Don't forget to catch it.

=== Retrieving information about the FM tuner ===

Now it's time to talk to the FM tuner. We do this by placing an ''ioctl'' call on the device. ''ioctl'' calls consist of a number (those we have defined above), and some argument. The argument is a pointer for passing a C structure to the driver. The driver may read from this structure or write into it.

A C structure can be built in Python with the ''struct'' module. Because the following ''ioctl'' call only retrieves information from the driver, we may provide an empty structure of the right size, like this:

info = struct.pack("84x")

Let's place the ''ioctl'' call, and retrieve the results. For unpacking the
structure, we have to provide the correct format string (see ''help(struct)'' for details):

<pre>
data = ioctl(radio_fd, _VIDIOC_G_TUNER, info)

# unpack the C struct
fields = struct.unpack("L32sLLLLLLll4L", data)
tuner_index = fields[0]
tuner_name = fields[1]
tuner_type = fields[2]
capability = fields[3]
rangelow = fields[4]
rangehigh = fields[5]
rxsubchans = fields[6]
audmode = fields[7]
signal = fields[8]
afc = fields[9]
</pre>

We should save the ''tuner_index'' and ''tuner_name'' for later, because this is how we address that particular tuner.

=== Setting the frequency ===

Next, we are going to tune into a radio station. For this, we have to set a frequency on the tuner. This is done by the V4L2 ''_VIDIOC_G_FREQUENCY'' ''ioctl'' invokation.

But a word of warning first: the driver doesn't take the frequency in KHz. You have to multiply your value with a constant factor first. The factor is either 0.016 or 16, depending on the device driver. On the N800, it is 16:

FREQ_FACTOR = 16

We are going to tune into 107.6 MHz now:

freq = 107600 * FREQ_FACTOR

Set up the C structure to pass to the driver:

data = struct.pack("LLL8L", tuner_index, tuner_type, freq, 0, 0, 0, 0, 0, 0, 0, 0)

Pass it to the driver:

ioctl(radio_fd, _VIDIOC_S_FREQUENCY, data)

=== Unmuting the tuner and setting the volume ===

You still don't hear anything from the radio. This is because the tuner is muted and its volume is set to 0. Let's change this:

Unmuting is easy:

data = struct.pack("Ll", _V4L2_CID_AUDIO_MUTE, 0)
ioctl(radio_fd, _VIDIOC_S_CTRL, data)

Changing the volume requires us to open the mixer device:

mixer_fd = os.open("/dev/mixer", os.O_RDONLY)

Now we can set the volume for the left and right speaker:

left_volume = 50
right_volume = 50

... and send it to the driver:

data = struct.pack("bb", left_volume, right_volume)
ioctl(mixer, _SOUND_MIXER_WRITE | _SOUND_MIXER_FMRADIO, data)

Don't forget to close the mixer device after this:

os.close(mixer_fd)

Now you can listen to the radio.

=== Cleaning up ===

When you have finished listening to the radio, you should clean up and
close the device again.

It's important to mute the radio, or you will hear it forever.

data = struct.pack("Ll", _V4L2_CID_AUDIO_MUTE, 1)
ioctl(radio_fd, _VIDIOC_S_CTRL, data)

And don't forget to close the device:

os.close(radio_fd)

== Code ready for use ==

There is a pure Python module available for controlling the FM tuner. It's based on the information here.
You can get it from [http://pyfmradio.garage.maemo.org the PyFMRadio project page].

[[Category:Development]]
[[Category:Midgard wiki]]