[alsa-devel] recording problem in beagleboard-mcbsp

[Peter Ujfalusi]

On 04/14/2015 07:41 PM, Variksla wrote:
>> In McBSP3 master mode, you need:
>> OMAP3_CORE1_IOPAD(0x2172, PIN_INPUT | MUX_MODE0) /* mcbsp3_fsx.mcbsp3_fsx */
>> OMAP3_CORE1_IOPAD(0x2178, PIN_INPUT | MUX_MODE1) /* uart2_tx.mcbsp3_clkx */
>> OMAP3_CORE1_IOPAD(0x2174, PIN_OUTPUT | MUX_MODE1) /* uart2_cts.mcbsp3_dx */
>> OMAP3_CORE1_IOPAD(0x2176, PIN_INPUT | MUX_MODE1)  /* uart2_rts.mcbsp3_dr */
> 
> Weird. If mcbsp3 is master I am wondering why we are configuring fsx and clkx as input. 

When we configure the pads, we set the input enable bit which will set the pin
to bidirectional mode.
The 4pin McBSP ports will get their FSR/CLKR from the actual pin. If the pin
is set to output only, no signal will come back to McBSP -> capture will not
work. This is why we need to set input enable, so that the signal going out
will be able to get back to McBSP's FSR/CLKR internal line.

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