On 11.11.2013 15:40, Antti Palosaari wrote:
On 11.11.2013 15:14, Hans Verkuil wrote:
On 11/10/2013 06:16 PM, Antti Palosaari wrote:
Convert unsigned 8 to float 32 [-1 to +1], which is commonly
used format for baseband signals.
I am also going to make some tests to find out if actual float
conversion is faster against pre-calculated LUT, in Kernel or in
libv4lconvert and so. Worst scenario I have currently is Mirics ADC with
14-bit resolution => 16384 quantization levels => 32-bit float LUT will
be 16384 * 4 = 65536 bytes. Wonder if that much big LUT is allowed to
library - but maybe you could alloc() and populate LUT on the fly if
needed. Or maybe native conversion is fast enough.
That integer to float conversion uses quite much CPU still, even I use
only 2M sampling rate.
When I do it inside Kernel, in URB completion handler at the same time
when copying data to videobuf2, using pre-calculated LUTs and using mmap
it eats 0.5% CPU to transfer stream to app.
When I do same but using libv4lconvert as that patch, it takes ~11% CPU.
And it was only 2M sampling rate, Mirics could go something like 15M.
I wonder if I can optimize libv4lconvert to go near in Kernel LUT
conversion...
CPU: AMD Phenom(tm) II X4 955 Processor
regards
Antti
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http://palosaari.fi/
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