humpback-dds/src/fpga.rs

use embedded_hal::{
    digital::v2::{OutputPin, InputPin},
    blocking::spi::Transfer,
    blocking::delay::DelayUs,
};

#[derive(Debug)]
pub enum FPGAFlashError {
    SPICommunicationError,
    NegotiationError,
    ResetStatusError,
}

const DATA: &'static [u8] = include_bytes!("../build/top.bin");

// A public method to flash iCE40 FPGA on Humpback
pub fn flash_ice40_fpga<SPI: Transfer<u8>,
                        SS: OutputPin,
                        RST: OutputPin,
                        DELAY: DelayUs<u32>,
                        DONE: InputPin>
    (mut spi: SPI, mut ss: SS, mut creset: RST, cdone: DONE, mut delay: DELAY) -> Result<(), FPGAFlashError>
{
    // Data buffer setup
    let mut dummy_byte :[u8; 1] = [0x00];
    let mut dummy_13_bytes :[u8; 13] = [0x00; 13];

    // Drive CRESET_B low
    creset.set_low()
            .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Drive SPI_SS_B low
    ss.set_low()
        .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Wait at least 200ns
    delay.delay_us(1_u32);

    // Drive CRESET_B high
    creset.set_high()
            .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Wait at least another 1200us to clear internal config memory
    delay.delay_us(1200_u32);

    // Before data transmission starts, check if C_DONE is truly low
    // If C_DONE is high, the FPGA reset procedure is unsuccessful
    match cdone.is_low() {
        Ok(true) => {},
        _ => return Err(FPGAFlashError::ResetStatusError),
    };

    // Set SPI_SS_B high
    ss.set_high()
        .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Send 8 dummy clock, effectively 1 byte of 0x00
    spi.transfer(&mut dummy_byte)
        .map_err(|_| FPGAFlashError::SPICommunicationError)?;

    // Drive SPI_SS_B low
    ss.set_low()
        .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Send the whole image without interruption
    for byte in DATA.into_iter() {
        let mut single_byte_slice = [*byte];
        spi.transfer(&mut single_byte_slice)
            .map_err(|_| FPGAFlashError::SPICommunicationError)?;
    }

    // Drive SPI_SS_B high
    ss.set_high()
        .map_err(|_| FPGAFlashError::NegotiationError)?;

    // Send at another 100 dummy clocks (choosing 13 bytes)
    spi.transfer(&mut dummy_13_bytes)
        .map_err(|_| FPGAFlashError::SPICommunicationError)?;

    // Check the CDONE output from FPGA
    // CDONE needs to be high
    match cdone.is_high() {
        Ok(true) => {},
        _ => return Err(FPGAFlashError::ResetStatusError),
    };

    // Send at least another 49 clock cycles to activate IO pins (choosing same 13 bytes)
    spi.transfer(&mut dummy_13_bytes).map_err(|_| FPGAFlashError::SPICommunicationError)?;
    Ok(())

}