On 01/15/2014 03:48 PM, Anssi Hannula wrote:
15.01.2014 13:27, Jyri Sarha kirjoitti:
On 12/31/2013 03:25 PM, Mark Brown wrote:
On Fri, Dec 20, 2013 at 12:39:38PM +0200, Jyri Sarha wrote:
support. The only supported sample format is SNDRV_PCM_FORMAT_S32_LE.
The 8 least significant bits are ignored.
Where does this constraint come from?
From driver/gpu/drm/i2c/tda998x_drv.c. The driver configures CTS_N
register statically to a value that works only with 4 byte samples.
According to my tests it is possible to support 3 and 2 byte samples too
by changing the CTS_N register value, but I am not sure if the
configuration can be changed on the fly. My data sheet of the nxp chip
is very vague about the register definitions, but I suppose the register
configures some clock divider on the chip. HDMI supports only upto 24bit
audio and the data sheet states that any extraneous least significant
bits are ignored.
That sounds strange, CTS/N values only depend on audio sample rate and
TMDS/video clock, not on the audio format or the size of samples (HDMI
spec sec 7.2 - Audio Sample Clock Capture and Regeneration).
Sure there isn't anything more going on (like the used HDMI sink being
more tolerant to wrong CTS/N with 4-byte samples, or more likely
something else I can't immediately think of)?
On theoretical level I am not really sure about anything, because have
not been able to get my hands on proper NXP TDA19988 documentation.
However, while playing around with my Beaglebone-Black I have have found
out in practice that by changing CTS_N register's (page 0x11 reg 0x0c)
K_SEL bits (bit 2 to 0)[1] I can get 2, 3 and 4 byte samples to work
consistently by setting:
K_SEL = 1 for SNDRV_PCM_FORMAT_S16_LE
K_SEL = 2 for SNDRV_PCM_FORMAT_S24_3LE
K_SEL = 3 for SNDRV_PCM_FORMAT_S32_LE
Because I do not really know what is going on, I did not want to suggest
any changes to the driver and just use the format that works with the
current driver version.
The HDMI sinks I have been using are a Toshiba 22B2LF1G and Thomson
42E90NF32 televisions. About those I just know that they both behave the
same way.
Best regards,
Jyri
[1] The closest data sheet that has any description about the chip
registers I have found is this:
http://media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/TDA9983B.pdf
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