Bill Tracey wrote:
With the FPGA based sound I/O work we're doing, independent D/A channels
are fairly easy, just instantiate a PWM decoder in the FPGA and an R and
C in hardware can be used as an output channel.
Can I have one *now*, please? ;-)
If that's the case, then it's probably time to start thinking about a
convention for sub-audio-rate control streams. The implication is that
arbitrary external control devices are going to be an increasingly
important part of an average system.
Let's suppose that, in a couple of years, a typical amateur SDR system
will be running 4 channels in and out at 192kHz sampling rate. With
256-frame buffers you get 1 buffer every 1.34ms. That's an effective
buffer rate of 750Hz.
750Hz is *way* fast for most of the things you'll be wanting to control
on the fly with your external control devices. (NB we're not talking
about CW keying here -- we mean things like moving sliders around to
control perceived spatial origin, etc.) Furthermore, viewed from the
buffer rate upwards, controller events are seriously asynchronous.
I'm betting that a basic control stream sampling rate of 100Hz is
plenty. Let's say we want to allow up to 128 independent control streams
to be handled at that fundamental rate, irrespective of source
(physically co-located, networked, etc.)
Any of you protocol-gedankenexperiment freaks out there want to chew on
this one for awhile?
73
Frank
AB2KT
