[alsa-devel] [PATCH 1/2] blackfin I2S(TDM mode) CPU DAI driver

Barry Song 21cnbao at gmail.com
Mon Jul 27 18:32:01 CEST 2009

2009/7/27 Mark Brown <broonie at opensource.wolfsonmicro.com>:
> On Mon, Jul 27, 2009 at 06:00:48PM +0800, Barry Song wrote:
>> 2009/7/25 Mark Brown <broonie at opensource.wolfsonmicro.com>:
>> > Looking at the code it appears that the main difference is that your TDM
>> > mode always configures the DMA layout for 8 channel blocks.  This
>> I2S is not a special case of TDM with only left and right two slots
>> for SPORT interface. I2S coordinates with TDM in SPORT, but not a part
>> of TDM. TDM require different hardware configuration with I2S, not
>> only different slot number.
>> One is "Stereo Serial Operation" mode of SPORT, the other one is
>> "Multichannel Operation" mode. They are incompatible at the same time.
> Right, but that's something I'd expect to be handleable at run time -
> and in any case, the multi-channel varaint can drop down to only two
> channels.
>> Mainly due to hardware, it's really difficult for us to control the
>> memory layout on the fly. That causes much trouble in hardware and
>> driver reliability. Datasheet claims DMA buffer should be fixed while
>> SPORT is enabled, but also claims the layout may be changed while
>> SPORT is disabled. So it's maybe possible for us to change the SPORT
>> api to support the configuration on the fly with a SPORT shutdown,
>> then i2s, tdm even ac97 can all use them to reduce the amount of code
>> duplication. But it need much work on debugging and testing to make it
>> work and reliable. So how about to patch it later as an individual
>> project since the changes will involve sport, i2s, ac97 and tdm?
> OK, if the hardware is as difficult to use as that I guess the current
> situation is adequate.  I'll check over your patch later but the code
> was almost ready last time so I don't anticipate any problems.
> However...
>> >> On the other hand, hardware board connection decides the I2S/TDM mode
>> >> directly. It's needless to switch between I2S and TDM dynamically. For
>> >> TDM mode, board driver can refer to the TDM instance, for I2S mode,
>> >
>> > Are you saying that a physically different SPORT or other hardware
>> > configuration on the CPU is required to use TDM mode?  The impression
>> > given by the drivers has always been that this is some kind of generic
>> > synchronous serial port and the way the SPORT number is set up seems to
>> > support that.  Could you go into more detail here, please - this would
>> > be a very unusual implementation decision for a CPU.
>> Here I means the different hardware configuration, and the semantic of
>> pins has some differences too for I2S and TDM.
> ...are you sure there's a different meaning for the external pins - what
> are these differences?  If they're not just related to the number of bit
> clock cycles per frame clock then are you sure it will interoperate with
> other DSP mode devices?
The main differences are the usages.
For I2S mode, each SPORT has two sets of independent transmit and
receive pins. Every set of pins support a stereo receive or transmit.
So a typical hardware connection to support multi-channels in I2S mode
is like attached "I2S.gif". Many pins are connected, and the main
characteristic is using multi-sets of pins concurrently. And in the
codec side, DSDATA1-n get the semantic as "DACx Data In", ASDATA1-n
are "ADCx Data Out".
For TDM mode, the main characteristic is using time-sharing to a set
of pins. A typical connection for TDM is like "tdm.gif". Only
tx/rx/clk/sync are connected to codec.  And in codec side, DSDATA1
gets the semantic as "DAC TDM Data In", DSDATA2-n are not "DACx Data
In" again. ASDATA1 becomes "ADC TDM Data Out", ASDATA2-n are not "ADCx
Data Out" again. And another difference is when multichannel mode is
enabled on a SPORT, both the transmitter and the receiver use RFS,
which is only a receive sync in I2S mode, as a frame sync. The RFS
signal is used to synchronize the channels and restart each
multichannel sequence. TFS, which is "Transmit Frame Sync" in I2S
mode, becomes TDV "transmit data valid" for external logic in TDM.
In TDM mode, the SPORT can interoperate with other DSP mode devices
considering they are using "tx/rx/clk/sync" pins. That's very common.

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