73 строки
1,5 КиБ
Go
73 строки
1,5 КиБ
Go
// +build !baremetal sam stm32 fe310
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package machine
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import "errors"
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// SPI phase and polarity configs CPOL and CPHA
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const (
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Mode0 = 0
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Mode1 = 1
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Mode2 = 2
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Mode3 = 3
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)
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var (
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ErrTxInvalidSliceSize = errors.New("SPI write and read slices must be same size")
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)
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// Tx handles read/write operation for SPI interface. Since SPI is a syncronous write/read
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// interface, there must always be the same number of bytes written as bytes read.
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// The Tx method knows about this, and offers a few different ways of calling it.
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//
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// This form sends the bytes in tx buffer, putting the resulting bytes read into the rx buffer.
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// Note that the tx and rx buffers must be the same size:
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//
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// spi.Tx(tx, rx)
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//
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// This form sends the tx buffer, ignoring the result. Useful for sending "commands" that return zeros
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// until all the bytes in the command packet have been received:
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//
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// spi.Tx(tx, nil)
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//
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// This form sends zeros, putting the result into the rx buffer. Good for reading a "result packet":
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//
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// spi.Tx(nil, rx)
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//
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func (spi SPI) Tx(w, r []byte) error {
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var err error
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switch {
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case w == nil:
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// read only, so write zero and read a result.
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for i := range r {
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r[i], err = spi.Transfer(0)
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if err != nil {
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return err
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}
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}
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case r == nil:
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// write only
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for _, b := range w {
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_, err = spi.Transfer(b)
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if err != nil {
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return err
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}
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}
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default:
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// write/read
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if len(w) != len(r) {
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return ErrTxInvalidSliceSize
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}
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for i, b := range w {
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r[i], err = spi.Transfer(b)
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if err != nil {
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return err
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}
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}
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}
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return nil
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}
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