Fixed point + NEON
Coder, interleaver, mapper and IFFT are fixed point. The Stockham radix-4 IFFT uses NEON and is bit-identical to the C reference (same checksum on x86 and ARM).
Firmware & technology
Over USB the Pluto sustains only about 7 MS/s, while 8 MHz DVB-T needs 9.14 MS/s. So the modulator runs on the device itself.
- PC / WSLffmpeg + TSDuck: video, audio, SI tables, constant bitrate
- UDPTransport stream up to 32 Mbit/s over USB networking
- Pluto ARMCore 0: RS, interleaver, convolutional code, mapper · core 1: NEON IFFT
- DAC → HFAD9364, 70 MHz–6 GHz, attenuation 0–89.75 dB
Real time on 2 cores
8k/64-QAM/7/8 runs at real-time factor 1.00 with zero underruns at 55–67 % load per Cortex-A9 core. DVB-S at 22 MBd uses 42–63 % of one core; DVB-S2 QPSK reaches 27 MBd on one core.
Firmware based on v0.31
Buildroot 2019.02, Linux 4.14 and FPGA bitstream identical to stock, plus libiio/iiod 0.25, real-time and DMA tuning and a device agent with an HTTP API.
Checked against a reference
Pilots, TPS and data carriers match gr-dtv. Self-reception via the RX input decodes bit-exact. The firmware can be tested from RAM first without changing the flash.
| Constellation | 1/2 | 2/3 | 3/4 | 5/6 | 7/8 |
|---|---|---|---|---|---|
| QPSK | 6,03 | 8,04 | 9,05 | 10,05 | 10,56 |
| 16-QAM | 12,06 | 16,09 | 18,10 | 20,11 | 21,11 |
| 64-QAM | 18,10 | 24,13 | 27,14 | 30,16 | 31,67 |
Inside
Monitoring, test record and media
