Hi all,
after some discussion with Dieter and Christian, the following strategy
has been selected for USB driver/protocol development:
0) Implement a composite USB Audio and CDC-ACM (serial) device to the
OS, where USB audio is used for complex xamples in S16_LE format,
and CDC-ACM is used for control of the device (tuning, etc.)
1) use USB audio with 1Ms/s, maybe even 2Ms/s for Linux.
2) offer the highest possible sample rate that windows supports as
alternative sample rate in the descriptor (96 or 128 kHz)
* implement a factor 10 decimation and low-pass inside the FPGA
to avoid folding of the spectrum, as the E4000 has a minimum filter
width of 1 MHz
3) implement a libusb-win32 (libusb-0.1) driver for windows for the
higher baud rates. To make sure this driver can bind to the device
(and not the standard windows usb audi driver), we can implement a
control command sent over the serial port, which causes the device to
re-enumerate and no longer identify itself as a 'usb audio class'.
The next steps in the direction of the firmware will be:
* creating the dual sample rate USB audio descriptors and verify they
are accepted by Linux and Windows (with dieters help)
* creating the descriptors for the composite device, validating them on
Linux and Windows, as well as operation of the virtual serial port
* experiments with the NuttX port for sam3u (might be nice, but I doubt
we will need it, given the single-purpose nature of the device)
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
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