Hi Péter,
On 3/19/24 19:29, Péter Ujfalusi wrote:
On 15/03/2024 13:27, Bastien Curutchet wrote:
The McBSP's DX pin that outputs serial data during playback streams can
be used during capture streams to repeatedly output a chosen pattern.
For instance, this can be useful to drive an active-low signal during
captures (by choosing <0> as output pattern).
Are there really any other use of this than to pull down or up the DX
pin (0 or 0xffff)
I don't know, indeed today I can only think about these two patterns.
I tried to do something in a 'generic' way so it can evolve if needed.
If you just use the pin as GPIO then you don't need to change anything
in the driver, The playback would not erach the pin, so no need to block it.
Enable this behaviour when the device-tree property 'ti,drive-dx' is
present. DX pin is driven with the provided pattern every time a
capture stream is launched.
It is an interesting use of the hardware... You are controlling an
external device (light an LED when capture is on)?
Yes I control the chip select pin of the ADC that is sending data to DR
pin, that's why I need the DX pin to be synchronized with capture
streams.
This property is not compatible with classic playback stream so
davinci_i2s_trigger() returns an error if a playback stream is started
while 'ti,drive-dx' flag is present.
Propbaly add the .startup() callback and block the playback right there?
Ok, TBH my mastery of the sound subsystem is not high enough to have an
opinion of where this should go so I'll trust you on this.
This has been tested on a board designed of a DAVINCI/OMAP-L138 where
the DX pin is linked to the chip select pin of the converters of the
capture side.
Isn't the DX will be pulled down as soon as the McBSP is enabled?
Can you just re-configure the PUPD_SEL for the pin group to make the pin
to be pulled the other way?
Well, the acquisition chain in my use case is a bit convoluted. The DX
pin's main purpose is to drive ADC chip select but it is also connected
to other components and all this needs synchronization upon captures.
I'll integrate your feedback about the code in next iteration, thank
you.
Best regards,
Bastien
