Since we are using the 'hw' interface of ALSA, we don't have the luxury of
samplerate conversion, given by the 'plughw' interface. If we try to set a
samplerate that is not supported, ALSA will just throw an error.
We can test for the supported samplerates, and create a list of supported
samplerates, then limit the selection to only those values. The frontend can
query the list of supported samplerates.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
The alsa driver requested signed 16-bit integers from ALSA, but casted them to
to an unsigned 16bit before finally casting them to a float. The end result was
that half of the wave would be clipped off.
We also requested data in little endian format. ALSA can be instructed to send
data with the correct endianness for the platform, without needing to worry
about what that is.
This patch attempts three points, which, together, fix the acquisition:
1) Request data from ALSA without specifying endianness; ALSA will handle the
endianness.
2) Simplify the int16_t to float loop by using straightforward indexes.
3) Normalize every value before sending it on the session bus.
NOTE: If testing with PulseView, it will appear as if sigrok is sending all
zeroes. sigrok is sending correct data, but since the data is normalized,
PulseView will incorrectly plot it as a straight line.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
The alsa driver only works with device "default". This limits the driver's
scope to whatever device ALSA deems to be "default". It is desirable to have
access to all ALSA devices from sigrok.
Change the alsa device scan so that:
Each alsa device (not alsa card) gets its own sigrok device
For example,
hw:1,0 == sigrok device 0
hw:1,1 == sigrok device 1
hw:2,0 == sigrok device 2
hw:2,1 == sigrok device 3
hw:2,2 == sigrok device 4
[...]
We don't currently look at alsa subdevices. We only use subdevice 0.
Every input device will have its own channels (left, right, etc). Each of
those channels gets mapped to a different sigrok probe. A device with 4
channels will have 4 probes from sigrok's perspective.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
snd_pcm_hw_params_set_rate_near() will try to use the samplerate closest to the
given value, potentially starting the acquisition with a different samplerate
than the one specified.
Instead, use snd_pcm_hw_params_set_rate(). It will return an error if the
samplerate is not supported by the hardware, which is arguably better than
collecting data with a different samplerate than the one specified.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
This is the driver model agreed upon for all drivers.
As a result of the split, a devc->num_probes field had to be added in order to
reduce the interdependence between api.c and protocol.c .
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Bert Vermeulen
Uwe Hermann
Alexandru Gagniuc