How to use SPI Half-Duplex Mode about esp-idf-hal HOT 4 OPEN

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.

from esp-idf-hal.

        .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))?;

from esp-idf-hal.

        .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.

from esp-idf-hal.

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.

from esp-idf-hal.