dma.rs

   let mut pwm = Pca9685::new(i2c, 0x40).unwrap();
    pwm.enable().unwrap();
    pwm.set_output_driver(pwm_pca9685::OutputDriver::TotemPole).unwrap();
    pwm.set_output_logic_state(pwm_pca9685::OutputLogicState::Inverted).unwrap();
    pwm.set_disabled_output_value(pwm_pca9685::DisabledOutputValue::HighImpedance).unwrap();
    pwm.enable_register_autoincrement().unwrap();

    // dma the led states
    let mut i2c = pwm.destroy();
    i2c.tx_dma(true);
    let streams = StreamsTuple::new(dp.DMA1, ccdr.peripheral.DMA1);
    let config = DmaConfig::default();
    let mut transfer: Transfer<_, _, MemoryToPeripheral, _, _> = Transfer::init(
        streams.6,
        i2c,
        unsafe { transmute::<&mut LedArray, &mut [u8; 65]>(&mut LED_BUFFER) },
        None,
        config,
    );
    transfer.start(|i2c| {
        i2c.master_write(0x00, 65, i2c::Stop::Automatic);
    });