new alsa driver for ti omap chip

new alsa driver for ti omap chip

[Gupta, Kshitij]

hi,

	I am trying to write an alsa driver for a tsc2101 codec on a arm
based SOC.  The control interface between the SOC and the tsc2101 codec is
via SPI. 
And the data interface is a I2S interface.  Can some one suggest a good
starting point to start such a driver.  
does sound/drivers/dummy.c makes sense for such a driver ???
warm regards
-kshitij


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Re: new alsa driver for ti omap chip

[Takashi Iwai]

At Thu, 12 Feb 2004 12:56:04 +0530,
Gupta, Kshitij wrote:
> 
> hi,
> 
> 	I am trying to write an alsa driver for a tsc2101 codec on a arm
> based SOC.  The control interface between the SOC and the tsc2101 codec is
> via SPI. 
> And the data interface is a I2S interface.  Can some one suggest a good
> starting point to start such a driver.  

some ALSA drivers use their own i2c functions, although there is a
generic i2c layer on linux kernel.  for example, delta.c or ews.c of
ice1712 driver use i2c (SPI) transfer (which calls ak4xxx-adda.c).
but it's rather complex to refer...

the i2c transfer is really easy to implement.  do just like the spec
says.  a pseudo code is like below.

	chip_select_low();
	udelay(1);

	for (i = 15; i >= 0; i--) {
		set_bit_clock(0);
		udelay(1);
		if (value_to_send & (1 << i))
			set_bit_data(1);
		else
			set_bit_data(0);
		udelay(1);
		set_bit_clock(0);
		udelay(1);
	}

	chip_select_high();


> does sound/drivers/dummy.c makes sense for such a driver ???

the dummy driver is irrelevant to the BUS type, so it makes some sense
to read the code :)


Takashi


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Re: new alsa driver for ti omap chip

[Jaroslav Kysela]

On Thu, 12 Feb 2004, Takashi Iwai wrote:

> At Thu, 12 Feb 2004 12:56:04 +0530,
> Gupta, Kshitij wrote:
> > 
> > hi,
> > 
> > 	I am trying to write an alsa driver for a tsc2101 codec on a arm
> > based SOC.  The control interface between the SOC and the tsc2101 codec is
> > via SPI. 
> > And the data interface is a I2S interface.  Can some one suggest a good
> > starting point to start such a driver.  
> 
> some ALSA drivers use their own i2c functions, although there is a
> generic i2c layer on linux kernel.  for example, delta.c or ews.c of
> ice1712 driver use i2c (SPI) transfer (which calls ak4xxx-adda.c).
> but it's rather complex to refer...
> 
> the i2c transfer is really easy to implement.  do just like the spec
> says.  a pseudo code is like below.
> 
> 	chip_select_low();
> 	udelay(1);
> 
> 	for (i = 15; i >= 0; i--) {
> 		set_bit_clock(0);
> 		udelay(1);
> 		if (value_to_send & (1 << i))
> 			set_bit_data(1);
> 		else
> 			set_bit_data(0);
> 		udelay(1);
> 		set_bit_clock(0);
> 		udelay(1);
> 	}
> 
> 	chip_select_high();

Note that I2S is not I2C. I2S is used to connect A/D and D/A converters 
(three wires - clock, l/r word and sample bit). We don't talk directly 
with any device over this serial bus.

I think that the driver must be written for a sound bridge between host
and the converters. In case of ARM platform, it's usually an integrated
serial controller which can do DMA transfers.

So, this I2S question is a bit irrelevant (it's for hardware designers, 
but not for driver developers).

Because I don't know the behaviour of the sound / serial bridge, I cannot 
suggest a driver, but if it's similar as ARM1100 architecture, then we 
have already a driver for it.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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Re: new alsa driver for ti omap chip

[Takashi Iwai]

At Thu, 12 Feb 2004 12:22:31 +0100 (CET),
Jaroslav wrote:
> 
> On Thu, 12 Feb 2004, Takashi Iwai wrote:
> 
> > At Thu, 12 Feb 2004 12:56:04 +0530,
> > Gupta, Kshitij wrote:
> > > 
> > > hi,
> > > 
> > > 	I am trying to write an alsa driver for a tsc2101 codec on a arm
> > > based SOC.  The control interface between the SOC and the tsc2101 codec is
> > > via SPI. 
> > > And the data interface is a I2S interface.  Can some one suggest a good
> > > starting point to start such a driver.  
> > 
> > some ALSA drivers use their own i2c functions, although there is a
> > generic i2c layer on linux kernel.  for example, delta.c or ews.c of
> > ice1712 driver use i2c (SPI) transfer (which calls ak4xxx-adda.c).
> > but it's rather complex to refer...
> > 
> > the i2c transfer is really easy to implement.  do just like the spec
> > says.  a pseudo code is like below.
> > 
> > 	chip_select_low();
> > 	udelay(1);
> > 
> > 	for (i = 15; i >= 0; i--) {
> > 		set_bit_clock(0);
> > 		udelay(1);
> > 		if (value_to_send & (1 << i))
> > 			set_bit_data(1);
> > 		else
> > 			set_bit_data(0);
> > 		udelay(1);
> > 		set_bit_clock(0);
> > 		udelay(1);
> > 	}
> > 
> > 	chip_select_high();
> 
> Note that I2S is not I2C. I2S is used to connect A/D and D/A converters 
> (three wires - clock, l/r word and sample bit). We don't talk directly 
> with any device over this serial bus.
> 
> I think that the driver must be written for a sound bridge between host
> and the converters. In case of ARM platform, it's usually an integrated
> serial controller which can do DMA transfers.
> 
> So, this I2S question is a bit irrelevant (it's for hardware designers, 
> but not for driver developers).

oh yes, it has nothing to do with I2S, of course.  sorry for
confusion.

but, about the SPI mode to control the chip (not DMA transfer), you
can still check the files above.


Takashi


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RE: new alsa driver for ti omap chip

[Gupta, Kshitij]

hi,

	yeah that's true I2S has not much to with the driver.  So there is
one more component on the chip called McBSP(Multichannel Buffered serial
port) which will actually communicate to the codec chip over I2S protocol.
And the DMA can read data from the McBSP recieve and transmit buffers. But
still the driver has to do the McBSP configuration. 
The kind of functionality the driver should provide is 

- Codec Control
	xxx_codec_write
	xxx_codec_read
for reading and writing to the codec control bits.  This will be done via
SPI interface.

- Dma Control functions
	start_dma
	queue_dma
	stop_dma ...

And all the ALSA based functions for init, read , write etc.....

regards
-kshitij

-----Original Message-----
From: Jaroslav Kysela [mailto:perex@suse.cz]
Sent: Thursday, February 12, 2004 4:53 PM
To: Takashi Iwai
Cc: Gupta, Kshitij; 'alsa-devel@lists.sourceforge.net'
Subject: Re: [Alsa-devel] new alsa driver for ti omap chip


On Thu, 12 Feb 2004, Takashi Iwai wrote:

> At Thu, 12 Feb 2004 12:56:04 +0530,
> Gupta, Kshitij wrote:
> > 
> > hi,
> > 
> > 	I am trying to write an alsa driver for a tsc2101 codec on a arm
> > based SOC.  The control interface between the SOC and the tsc2101 codec
is
> > via SPI. 
> > And the data interface is a I2S interface.  Can some one suggest a good
> > starting point to start such a driver.  
> 
> some ALSA drivers use their own i2c functions, although there is a
> generic i2c layer on linux kernel.  for example, delta.c or ews.c of
> ice1712 driver use i2c (SPI) transfer (which calls ak4xxx-adda.c).
> but it's rather complex to refer...
> 
> the i2c transfer is really easy to implement.  do just like the spec
> says.  a pseudo code is like below.
> 
> 	chip_select_low();
> 	udelay(1);
> 
> 	for (i = 15; i >= 0; i--) {
> 		set_bit_clock(0);
> 		udelay(1);
> 		if (value_to_send & (1 << i))
> 			set_bit_data(1);
> 		else
> 			set_bit_data(0);
> 		udelay(1);
> 		set_bit_clock(0);
> 		udelay(1);
> 	}
> 
> 	chip_select_high();

Note that I2S is not I2C. I2S is used to connect A/D and D/A converters 
(three wires - clock, l/r word and sample bit). We don't talk directly 
with any device over this serial bus.

I think that the driver must be written for a sound bridge between host
and the converters. In case of ARM platform, it's usually an integrated
serial controller which can do DMA transfers.

So, this I2S question is a bit irrelevant (it's for hardware designers, 
but not for driver developers).

Because I don't know the behaviour of the sound / serial bridge, I cannot 
suggest a driver, but if it's similar as ARM1100 architecture, then we 
have already a driver for it.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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RE: new alsa driver for ti omap chip

[Jaroslav Kysela]

On Thu, 12 Feb 2004, Gupta, Kshitij wrote:

> hi,
> 
> 	yeah that's true I2S has not much to with the driver.  So there is
> one more component on the chip called McBSP(Multichannel Buffered serial
> port) which will actually communicate to the codec chip over I2S protocol.
> And the DMA can read data from the McBSP recieve and transmit buffers. But
> still the driver has to do the McBSP configuration. 
> The kind of functionality the driver should provide is 
> 
> - Codec Control
> 	xxx_codec_write
> 	xxx_codec_read
> for reading and writing to the codec control bits.  This will be done via
> SPI interface.

So, look to alsa-kernel/i2c directory for examples, how to write a library 
for such codecs. We prefer to create a library than controlling codecs in
the toplevel driver, because we can reuse code later.

> - Dma Control functions
> 	start_dma
> 	queue_dma
> 	stop_dma ...

Exactly. In this case, you may look to any ISA/PCI drivers what the 
callbacks from midlevel do.

If you have a specific question, we are here ;-)

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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