Class: SPI::Driver::SPIdev

Inherits:
Base
  • Object
show all
Defined in:
lib/spi/driver/spidev.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(args = {}) ⇒ SPIdev

Returns a new instance of SPIdev.

Raises:


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# File 'lib/spi/driver/spidev.rb', line 10

def initialize(args={})
  raise SPIException, "No Device specified" if args[:device].nil?
  raise SPIException, "Device #{args[:device]} not found" unless File.exists?(args[:device])
  @device = File.open(args[:device])
  @mode=getMode
  @bits=getBits
  @speed=getSpeed
end

Instance Attribute Details

#bitsObject

Returns the value of attribute bits


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# File 'lib/spi/driver/spidev.rb', line 7

def bits
  @bits
end

#modeObject

Returns the value of attribute mode


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# File 'lib/spi/driver/spidev.rb', line 6

def mode
  @mode
end

#speedObject

Returns the value of attribute speed


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# File 'lib/spi/driver/spidev.rb', line 8

def speed
  @speed
end

Instance Method Details

#xfer(txdata: [], length: 0) ⇒ Object

By the length used will always be the greater of txdata.size and length. rxdata will be sized according to that maximum and txdata grown if needed


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# File 'lib/spi/driver/spidev.rb', line 39

def xfer(txdata: [], length: 0)
  # Ensure tx and rx buffers are the same size
  length = txdata.size if txdata.size > length
  txdata += (Array.new(length-txdata.size) {0}) if length > txdata.size
  rxdata  = (Array.new(length) { 0 })
  
  # TODO Use the bitstruct gem ?
  # https://rubygems.org/gems/bit-struct/versions/0.15.0
  # Or create a class to wrap access and pack/unpack

  txdata_pack       = txdata.pack('C*')     # __u64 (pointer to data)
  rxdata_pack       = rxdata.pack('C*')     # __u64 (pointer to data)

  # length                                  # __u32
  speed             = 0                     # __u32

  delay_usecs       = 0                     # __u16
  bits_per_word     = 0                     # __u8
  cs_change         = 0                     # __u8
  tx_nbits          = 0                     # __u8
  rx_nbits          = 0                     # __u8
  pad               = 0                     # __u16

  txdata_p = [txdata_pack].pack('P').unpack('L!')[0] # 64bit pointer to txdata
  rxdata_p = [rxdata_pack].pack('P').unpack('L!')[0] # 64bit pointer to rxdata

  # We might need to do something special with the txdata and rxdata pointers to make them 64 bit
  data = [txdata_p, rxdata_p, length, speed, delay_usecs, bits_per_word, cs_change, tx_nbits, rx_nbits, pad].pack('QQLLSCCCCS')

  # We're only going to handle one message at a time for now
  @device.ioctl(SPI_IOC_MESSAGE(1),data)

  return rxdata_pack.unpack('C*')
    
end