[Sound-open-firmware] How to check first frames on playback

[Paul Olaru]

What is a good way to check that the first frames when starting playback with a file
are correct and not reordered or repeated? I have tried to modify my host DMA driver
to dump the frames as it transfers them and I see that the data transferred is the same
as in the file but the first two frames are reordered and repeated, at least when I set
the buffer size to be very small in aplay (--buffer-size=96). My test is to attempt to play
a 768-byte raw file (2 channels, S16_LE) and dump all the data transferred by my host
DMA driver. From the dumps (within the limits of etrace; I don't have DMA trace working
as I didn't focus on that) I notice that several of the frames within the first period
(first 384 bytes) end up being repeated and in the wrong ordering.

The issue is unimportant with uncompressed playback as that would just be a small,
2ms glitch which is hardly audible, especially if you also have a volume ramp or the file
is silent or mostly silent in the beginning. However, I want to implement support for
compressed playback at some point which requires such glitches to not happen with
the data before it even enters the pipeline (any bit change will cause corruption which
is definitely audible or even failure of the decoding algorithm).

So how should I check that the first few frames during playback are actually the correct
ones?