devfs.go

Documentation: golang.org/x/exp/io/i2c

     1  // Copyright 2016 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build linux
     6  
     7  package i2c
     8  
     9  import (
    10  	"fmt"
    11  	"io"
    12  	"os"
    13  	"syscall"
    14  
    15  	"golang.org/x/exp/io/i2c/driver"
    16  )
    17  
    18  // Devfs is an I2C driver that works against the devfs.
    19  // You need to load the "i2c-dev" kernel module to use this driver.
    20  type Devfs struct {
    21  	// Dev is the I2C bus device, e.g. /dev/i2c-1. Required.
    22  	Dev string
    23  }
    24  
    25  const (
    26  	i2c_SLAVE  = 0x0703 // TODO(jbd): Allow users to use I2C_SLAVE_FORCE?
    27  	i2c_TENBIT = 0x0704
    28  )
    29  
    30  // TODO(jbd): Support I2C_RETRIES and I2C_TIMEOUT at the driver and implementation level.
    31  
    32  func (d *Devfs) Open(addr int, tenbit bool) (driver.Conn, error) {
    33  	f, err := os.OpenFile(d.Dev, os.O_RDWR, os.ModeDevice)
    34  	if err != nil {
    35  		return nil, err
    36  	}
    37  	conn := &devfsConn{f: f}
    38  	if tenbit {
    39  		if err := conn.ioctl(i2c_TENBIT, uintptr(1)); err != nil {
    40  			conn.Close()
    41  			return nil, fmt.Errorf("cannot enable the 10-bit address mode on bus %v: %v", d.Dev, err)
    42  		}
    43  	}
    44  	if err := conn.ioctl(i2c_SLAVE, uintptr(addr)); err != nil {
    45  		conn.Close()
    46  		return nil, fmt.Errorf("error opening the address (%v) on the bus (%v): %v", addr, d.Dev, err)
    47  	}
    48  	return conn, nil
    49  }
    50  
    51  type devfsConn struct {
    52  	f *os.File
    53  }
    54  
    55  func (c *devfsConn) Tx(w, r []byte) error {
    56  	if w != nil {
    57  		if _, err := c.f.Write(w); err != nil {
    58  			return err
    59  		}
    60  		c.f.Sync()
    61  	}
    62  	if r != nil {
    63  		if _, err := io.ReadFull(c.f, r); err != nil {
    64  			return err
    65  		}
    66  	}
    67  	return nil
    68  }
    69  
    70  func (c *devfsConn) Close() error {
    71  	return c.f.Close()
    72  }
    73  
    74  func (c *devfsConn) ioctl(arg1, arg2 uintptr) error {
    75  	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, c.f.Fd(), arg1, arg2); errno != 0 {
    76  		return syscall.Errno(errno)
    77  	}
    78  	return nil
    79  }
    80
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