Skip to content

linux.md

Latest commit

 

History

History
61 lines (38 loc) · 2.75 KB

linux.md

File metadata and controls

61 lines (38 loc) · 2.75 KB

Testing on Linux

While it poses limited to no utility for users, the Linux build may be very helpful for developers.

User interface testing

The openrtx_linux and openrtx_linux_mod17 targets may be used to validate changes to the UI without having to have a physical device present.

Testing Software-Decoded Baseband

The Linux build can demodulate a pre-recorded baseband file, which is useful for testing the receive path end-to-end without RF hardware.

Sample baseband files

The tests/unit/assets directory contains the following baseband recordings:

File Use
M17_test_baseband.raw Runtime demodulation; src callsign only
M17_test_baseband_dc.raw Runtime demodulation; src callsign only

Note: These test samples have a sample rate of 48kHz, and must be decimated to 24kHz before they can be demodulated with OpenRTX on Linux. See below for details.

Demodulating a raw baseband file with OpenRTX Linux

The Linux build uses a file source driver that reads, on loop, a raw 16-bit, little-endian, mono, 24 kHz file from /tmp/baseband.raw.

Decimation

The OpenRTX M17 modulator works at a sample rate of 48 kHz, but the demodulator works at a sample rate of 24 kHz. Because the sample baseband files have a sample rate of 48 kHz, they must be decimated to 24 kHz first in order to be demodulated. This can be done easily using the sox audio utility, available in most packagers. To decimate a sample baseband file, run:

# Convert the sample baseband recording from 48 kHz to 24 kHz
sox -r 48000 -e signed-integer -b 16 -c 1 tests/unit/assets/M17_test_baseband.raw \
    -r 24000 -e signed-integer -b 16 -c 1 M17_test_baseband_24k.raw \
    rate -v

Simply move the decimated file to /tmp/baseband.raw and launch the application in order for it to demodulate. Alternatively, you can set the output file path in sox to /tmp/baseband.raw directly and skip the copy step.

# Copy the sample to the path the file-source driver reads from:
cp M17_test_baseband_24k.raw /tmp/baseband.raw

# Build
meson setup build_linux
meson compile -C build_linux openrtx_linux

# Launch
./build_linux/openrtx_linux

In this example, a receive screen with callsign OPNRTX is expected:

Example demodulation

Note: Since the Linux build has no audio driver, it is not expected that received audio can be heard.

Going Further

In theory, you could create a named pipe at /tmp/baseband.raw and write to it using GNU Radio. Something like a source, with resampling to 24kHz if required, then float to short, then a file sink should work.