Update embedded-hal

[LehMaxence]

Removed write-only and read-only spi implementations
Handled Delay operation between transfers

[LehMaxence]

I tested this with hardware today on a Raspberry Pi 4 and a ADXL355 accelerometer connected over SPI with this code:

    let mut spi_dev = Spidev::open(SPI_PATH)?;
    let options = SpidevOptions::new()
        .bits_per_word(8)
        .max_speed_hz(10_000_000)
        .mode(SpiModeFlags::SPI_MODE_0)
        .build();
    spi_dev.configure(&options)?;

    let mut buf_1 = [0u8; 1];
    let mut buf_2 = [0u8; 1];

    let mut operations = [
        SpiOperation::DelayUs(1_000_000),
        SpiOperation::Write(&[(0x2D << 1), 0x01]),
        SpiOperation::DelayUs(500),
        SpiOperation::Write(&[(0x2D << 1) | 0x01]),
        SpiOperation::Read(&mut buf_1),
        SpiOperation::DelayUs(500),
        SpiOperation::Write(&[(0x2D << 1), 0x00]),
        SpiOperation::DelayUs(500),
        SpiOperation::Write(&[(0x2D << 1) | 0x01]),
        SpiOperation::Read(&mut buf_2),
        SpiOperation::DelayUs(5_000_000),
    ];

    spi_dev.transaction(&mut operations)?;

    println!("buf_1: {:X}", buf_1[0]);
    println!("buf_2: {:X}", buf_2[0]);

It worked as expected.

[eldruin]

Thank you for your work here.
Unfortunately, this approach is suboptimal in that it requires multiple transfers and flushes on the bus every time there is a delay, even though the underlying linux device supports delay transfers.

The optimal approach here would be to first extend spidev: rust-embedded/rust-spidev#40 to support delay operations and then updating this crate in line with what was outlined in: #87 (comment)

Sorry for the confusion and lack of more explicit guidance.

[LehMaxence]

Thanks for the feedback! I agree with you.
I'll wait for the rust-spidev update and then update this PR, or we can close it if you prefer.

[LehMaxence]

I chose to max out the delay to u16::MAX but that may not be what we want here.
Let me know what you think.

[eldruin]

I think we can leave at that here but please document in this method and in the Spidev struct that delays are capped to 65535 microseconds.

[eldruin]

Thank you!

[eldruin]

I think we can leave at that here but please document in this method and in the Spidev struct that delays are capped to 65535 microseconds.

[eldruin]

Sorry for the delay.
Looks good to me, thank you!

[eldruin]

Ach, CI has to be migrated to GitHub merge queue for this to be merged.

[eldruin]

@LehMaxence could you rebase this to master now that CI is fixed?

[LehMaxence]

@LehMaxence could you rebase this to master now that CI is fixed?

Rebased :-)

[eldruin]

Great, thank you!