spireg

Documentation

Overview

Package spireg defines the SPI registry for SPI ports discovered on the host.

Index

• func Open(name string) (spi.PortCloser, error)
• func Register(name string, aliases []string, number int, o Opener) error
• func Unregister(name string) error
• type Opener
• type Ref
  • func All() []*Ref

Examples

• All
• Open

Functions

func Open

func Open(name string) (spi.PortCloser, error)

Open opens a SPI port by its name, an alias or its number and returns an handle to it.

Specify the empty string "" to get the first available port. This is the recommended default value unless an application knows the exact port to use.

Each port can register multiple aliases, each leading to the same port handle.

"Bus number" is a generic concept that is highly dependent on the platform and OS. On some platform, the first port may have the number 0, 1 or as high as 32766. Bus numbers are not necessarily continuous and may not start at 0. It was observed that the bus number as reported by the OS may change across OS revisions.

A SPI port is constructed of the bus number and the chip select (CS) number.

When the SPI port is provided by an off board plug and play bus like USB via a FT232H USB device, there can be no associated number.

Example

// On linux, the following calls will likely open the same port.
Open("/dev/spidev1.0")
Open("SPI1.0")
Open("1")

// How a command line tool may let the user choose a SPI port, yet
// default to the first port known.
name := flag.String("spi", "", "SPI port to use")
flag.Parse()
b, err := Open(*name)
if err != nil {
	log.Fatal(err)
}
defer b.Close()

// Pass b to a device driver, or if using b directly, do:
c, err := b.DevParams(1000000, spi.Mode3, 8)
if err != nil {
	log.Fatal(err)
}
// Use b...
c.Tx([]byte("cmd"), nil)

func Register

func Register(name string, aliases []string, number int, o Opener) error

Register registers a SPI port.

Registering the same port name twice is an error, e.g. o.Name(). o.Number() can be -1 to signify that the port doesn't have an inherent "bus number". A good example is a port provided over a FT232H device connected on an USB bus. In this case, the port name should be created from the serial number of the device for unique identification.

Only ports with the CS #0 are registered with their number.

func Unregister

func Unregister(name string) error

Unregister removes a previously registered SPI port.

This can happen when a SPI port is exposed via an USB device and the device is unplugged.

Types

type Opener

type Opener func() (spi.PortCloser, error)

Opener opens an handle to a port.

It is provided by the actual port driver.

type Ref

type Ref struct {
	// Name of the port.
	//
	// It must not be a sole number. It must be unique across the host.
	Name string
	// Aliases are the alternative names that can be used to reference this port.
	Aliases []string
	// Number of the port or -1 if the port doesn't have any "native" number.
	//
	// Buses provided by the CPU normally have a 0 based number. Buses provided
	// via an addon (like over USB) generally are not numbered.
	//
	// The port is a bus number plus a CS line.
	Number int
	// Open is the factory to open an handle to this SPI port.
	Open Opener
}

Ref references a SPI port.

It is returned by All() to enumerate all registered ports.

func All

func All() []*Ref

All returns a copy of all the registered references to all know SPI ports available on this host.

The list is sorted by the port name.

Example

// Enumerate all SPI ports available and the corresponding pins.
fmt.Print("SPI ports available:\n")
for _, ref := range All() {
	fmt.Printf("- %s\n", ref.Name)
	if ref.Number != -1 {
		fmt.Printf("  %d\n", ref.Number)
	}
	if len(ref.Aliases) != 0 {
		fmt.Printf("  %s\n", strings.Join(ref.Aliases, " "))
	}

	b, err := ref.Open()
	if err != nil {
		fmt.Printf("  Failed to open: %v", err)
	}
	if p, ok := b.(spi.Pins); ok {
		fmt.Printf("  CLK : %s", p.CLK())
		fmt.Printf("  MOSI: %s", p.MOSI())
		fmt.Printf("  MISO: %s", p.MISO())
		fmt.Printf("  CS  : %s", p.CS())
	}
	if err := b.Close(); err != nil {
		fmt.Printf("  Failed to close: %v", err)
	}
}