[alsa-devel] davici-mcasp: "tx-num-evt" confusion with number of serializers

Michal Bachraty michal.bachraty at streamunlimited.com
Tue Feb 26 15:06:54 CET 2013

I'm  working on multichannel version of davinci-mcasp and also davinci-pcm. I 
have first version running and now I want to refine code. I found one confusion 
in davinci-mcasp with using of DT property "tx-num-evt".  In DT binding 
documentation "tx-num-evt" is defined as "FIFO levels", but in Mcasp src, there 
is code, which mixes tx-num-evt with number of serializers (i2s data lines) 
that are enabled for data playback and receive (dev->txnumevt * tx_ser)

mcasp_mod_bits(dev->base + MCASP_VER3_WFIFOCTL,
                (((dev->txnumevt * tx_ser) << 8), NUMEVT_MASK); 

>From dacinci pcm,  DMA data tranfer use txnumevt as number of serializers and 
also for data prefetching. 
I undestand definition "FIFO levels" as how many prefetched data are in FIFO. 
Prefetched data are for me frame data / 2  ( all left or right channels for 
one sampling time). This results me from AM335x FIFO documantation.
What is original purpose for "tx-num-evt" parameter?


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