Golang and SPI - trying to init RF522 drive

Question

I have a simple Python code that does initalize MFRC522 device properly:

    import spidev

    mode_reset = 0x0F

    def spi_transfer(data):
        r = spi.xfer2(data)
        return r

    def dev_write(address, value):
        r = spi_transfer([(address << 1) & 0x7E, value])
        print(">>",[(address << 1) & 0x7E, value], r)
        return r

    def reset():
        dev_write(0x01, mode_reset)

    spi = spidev.SpiDev()
    spi.open(0, 0)
    spi.max_speed_hz = 1000000
    print(spi.mode, spi.bits_per_word, spi.lsbfirst)
    reset()

that works perfectly fine - it returns the command code back 15, but the same initialization routine implemented in Go doesn't really work:

    package main

    import (
        "fmt"
        "golang.org/x/exp/io/spi"
        "log"
    )

    func main() {

        spiDev, err := spi.Open(&spi.Devfs{
            Dev:      "/dev/spidev0.0",
            Mode:     spi.Mode(spi.Mode0),
            MaxSpeed: int64(1000000),
        })

        spiDev.SetMode(spi.Mode0)
        spiDev.SetBitOrder(spi.MSBFirst)
        spiDev.SetBitsPerWord(8)

        if err != nil {
            log.Fatal(err)
        }

        writeSpiData := func(dataIn []byte) (out []byte, err error) {
            out = make([]byte, len(dataIn))
            err = spiDev.Tx(dataIn, out)
            return
        }

        devWrite := func(address int, data byte) (err error) {
            newData := [2]byte{(byte(address) << 1) & 0x7E, data}
            readBuf, err := writeSpiData(newData[0:])
            fmt.Println(">>", newData, readBuf)
            return
        }

        if err != nil {
            log.Fatal(err)
        }

        devWrite(0x01, 0x0F)

        fmt.Println("Done")

    }

This one returns [0 0] which is wrong. Does anyone know what might be wrong there?

Answer 1

It looks like the SPI module from Go distribution doesn't work as expected. I did some research using some logic analyzer and realized that the SPI command layer from exp/io/spi does not generate the appropriate commands.

The source code:

package main

import (
    "fmt"
    "golang.org/x/exp/io/spi"
    "log"
)

func main() {

    spiDev, err := spi.Open(&spi.Devfs{
        Dev:      "/dev/spidev0.0",
        MaxSpeed: int64(1000000),
    })

    spiDev.SetMode(spi.Mode0)
    spiDev.SetBitOrder(spi.MSBFirst)
    spiDev.SetBitsPerWord(8)

    if err != nil {
        log.Fatal(err)
    }

    writeSpiData := func(dataIn []byte) (out []byte, err error) {
        out = make([]byte, len(dataIn))
        err = spiDev.Tx(dataIn, out)
        return
    }

    devWrite := func(address int, data byte) (err error) {
        newData := [2]byte{(byte(address) << 1) & 0x7E, data}
        readBuf, err := writeSpiData(newData[0:])
        fmt.Println(">>", newData, readBuf)
        return
    }

    if err != nil {
        log.Fatal(err)
    }

    devWrite(0x01, 0x0F)

    fmt.Println("Done")

}

The resulting data log:

Now with another driver, https://github.com/ecc1/spi the code looks like:

package main

import (
    "fmt"
    "log"
    "github.com/ecc1/spi"
)

func main() {

    spiDev, err := spi.Open("/dev/spidev0.0", 1000000, 0)

    spiDev.SetMode(0)
    spiDev.SetBitsPerWord(8)
    spiDev.SetLSBFirst(false)
    spiDev.SetMaxSpeed(1000000)

    if err != nil {
        log.Fatal(err)
    }

    writeSpiData := func(dataIn []byte) (err error) {
        err = spiDev.Transfer(dataIn)
        return
    }

    devWrite := func(address int, data byte) (err error) {
        newData := [2]byte{(byte(address) << 1) & 0x7E, data}
        fmt.Print("<< ", newData, " ")
        err = writeSpiData(newData[0:])
        fmt.Println(">>", newData)
        return
    }

    if err != nil {
        log.Fatal(err)
    }

    devWrite(0x01, 0x0F)

    if err != nil {
        log.Fatal(err)
    }

}

And the resulting protocol dump is correct: