QUEEN WMS modulator/demodulator

• nucleo64 stm32f446
• rust

Design

Modulation

• GPIO PA15 square phase modulation ~100 kHz
• has zeros at even harmonics (dick-effect)
• maximum power in the relevant sidebands (especially given fixed amplitude, not fixed rms power), zero carrier, zero even harmonics

Detection

• PA0 ADC input
• sample rate ~1 MHz
• DMA

Demod, filtering

• frequency shifted rectangular window
• has zeros at multiples of the modulation (especially 2f/3f/dick-like effect)
• highest gain
• lowest noise bw
• scallopping loss not problematic
• sidelobes not problematic
• demodulation IQ or higher orders, or square, or dc/zero/avg

IIR filtering

• anything goes

Output

• DAC output PA4, PA5

Build

Features

• itm: use the ITM cell for debugging output
• simd: use DSP SIMDs for MACC
• bkpt: place breakpoints around the ISR for timing

Commands

rustup override add nightly
rustup install nightly
rustup target add thumbv7em-none-eabi

cargo install itm  # features=itm
mkfifo itm.fifo  # features=itm
openocd -f stm32f446-nucleo64.cfg
cargo run --release
itmdump -f itm.fifo

TODO

• ADC1,2 should be interleaved
  • use 15 sample+acquisition cycles, 17+x sample interval
  • use either
    • continuous mode with DDS
    • alternate trigger mode and a 1/n trigger from TIMx, TIMx synced to TIM2
• maybe:
  • interpolate DAC samples
  • DMA double buffer write to DAC with TIMy, TIMy synced to TIM2