How to use SPI Half-Duplex Mode

[Dessera]

I'm a beginner of rust embedded development of esp32. I want to drive DS1302 with Half3Wire-Duplex Mode, but code below didn't work.

use esp_idf_hal::{
    gpio::Gpio2,
    peripherals::Peripherals,
    spi::{
        config::{Mode as SpiMode, Phase, Polarity},
        SpiBusDriver, SpiConfig, SpiDeviceDriver, SpiDriver, SpiDriverConfig,
    },
};

fn main() -> anyhow::Result<()> {
    esp_idf_svc::sys::link_patches();
    esp_idf_svc::log::EspLogger::initialize_default();

    let peripherals = Peripherals::take()?;

    let config = SpiConfig::new()
        .allow_pre_post_delays(true)
        .input_delay_ns(4)
        .duplex(esp_idf_hal::spi::config::Duplex::Half3Wire)
        .cs_active_high();

    let spi_drv = SpiDriver::new(
        peripherals.spi2,
        peripherals.pins.gpio19,
        peripherals.pins.gpio3,
        None::<Gpio2>,
        &SpiDriverConfig::default(),
    )?;

    let mut spi_dev = SpiDeviceDriver::new(spi_drv, Some(peripherals.pins.gpio2), &config)?;

    let mut read_buf = [0u8; 16];
    log::info!("read_buf: {:?}", read_buf);
    spi_dev.transfer(&mut read_buf, &[0x80 | 0x01, 0x00])?;
    log::info!("read_buf: {:?}", read_buf);

    loop {
        esp_idf_hal::delay::FreeRtos::delay_ms(1000);
    }
}

The serial output is as follows

I (363) main_task: Calling app_main()
I (373) eclock_rs: read_buf: [0, 0]
E (373) spi_master: check_trans_valid(792): SPI half duplex mode is not supported when both MOSI and MISO phases are enabled.
I (383) gpio: GPIO[2]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 
I (393) gpio: GPIO[3]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 
I (403) gpio: GPIO[19]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0 
Error: ESP_ERR_INVALID_ARG
I (413) main_task: Returned from app_main()

It seems that I am missing some configurations, but I don't know what I'm missing.

[Vollbrecht]

Welcome and thanks for reporting.

I think there might be a bug inside the read path of the transfer, when used in half3wire mode , but have to investigate a bit further.

[Dominaezzz]

        .duplex(esp_idf_hal::spi::config::Duplex::Half3Wire)

and

    spi_dev.transfer(&mut read_buf, &[0x80 | 0x01, 0x00])?;

are incompatible.
You can't do a transfer with only one wire, you need one wire for reading and one wire for writing.

What you probably want to do there is this.

    spi_dev.transaction(&mut [Operation::Read(&mut read_buf), Operation::Write(&[0x80 | 0x01, 0x00]))?;

EDIT:

Actually, thinking about it a bit more, you're probably wanting to write first. Up to you to decide 😄

    spi_dev.transaction(&mut [Operation::Write(&[0x80 | 0x01, 0x00]), Operation::Read(&mut read_buf))?;

[Dessera]

        .duplex(esp_idf_hal::spi::config::Duplex::Half3Wire)

and

    spi_dev.transfer(&mut read_buf, &[0x80 | 0x01, 0x00])?;

are incompatible. You can't do a transfer with only one wire, you need one wire for reading and one wire for writing.

What you probably want to do there is this.

    spi_dev.transaction(&mut [Operation::Read(&mut read_buf), Operation::Write(&[0x80 | 0x01, 0x00]))?;

EDIT:

Actually, thinking about it a bit more, you're probably wanting to write first. Up to you to decide 😄

    spi_dev.transaction(&mut [Operation::Write(&[0x80 | 0x01, 0x00]), Operation::Read(&mut read_buf))?;

I tried to solve the problem with your code, but it returned the same error. When I did not select any Duplex (which should be Full-Duplex at this time), the final read_buf only has 0xF.

[Dominaezzz]

I see. Looks like @Vollbrecht discovered this as well.

From a quick glance it appears we should be setting this to zero in half duplex mode.

This comment should've been taken care of when half duplex was added in this PR. Though I'm a little surprised no one has encountered this issue yet.

[xiaguangbo]

I also have the same question,"Half3Wire" how to use?

[xiaguangbo]

solution: espressif/esp-idf#13554

[xiaguangbo]

new solution: #459

[Vollbrecht]

Closing as it is now merged! Thanks,