Wireshark dissector for DM9601 USB to Ethernet adapter chips

dm9601.lua

-- DM9601 dissector for Wireshark
--
-- Usage: wireshark -X lua_script:dm9601.lua
--
p_dm9601 = Proto("dm9601", "DM9601 USB Protocol")
p_dm9601_ethin = Proto("dm9601_ethin", "DM9601 USB Protocol Ethernet Input Stream")
p_dm9601_ethout = Proto("dm9601_ethout", "DM9601 USB Protocol Ethernet Output Stream")
p_dm9601_irq = Proto("dm9601_irq", "DM9601 USB Protocol Interrupts")

local operations = {
    [0xc000] = "READ_REGISTER()",
    [0x4001] = "WRITE_REGISTER()",
    [0x4003] = "WRITE1_REGISTER()",
    [0xc002] = "READ_MEMORY()",
    [0x4005] = "WRITE_MEMORY()",
    [0x4007] = "WRITE1_MEMORY()",
}

local regs = {
    [0x00] = "Network Control Register",
    [0x01] = "Network Status Register",
    [0x02] = "TX Control Register",
    [0x03] = "TX Status Register I",
    [0x04] = "TX Status Register II",
    [0x05] = "RX Control Register",
    [0x06] = "RX Status Register",
    [0x07] = "Receive Overflow Counter Register",
    [0x08] = "Back Pressure Threshold Register",
    [0x09] = "Flow Control Threshold Register",
    [0x0a] = "RX/TX Flow Control Register",
    [0x0b] = "EEPROM & PHY Control Register",
    [0x0c] = "EEPROM & PHY Address Register",
    [0x0d] = "EEPROM & PHY Data Register Low",
    [0x0e] = "EEPROM & PHY Data Register High",
    [0x0f] = "Wake Up Control Register",
    [0x10] = "Physical Address Byte 0 Register",
    [0x11] = "Physical Address Byte 1 Register",
    [0x12] = "Physical Address Byte 2 Register",
    [0x13] = "Physical Address Byte 3 Register",
    [0x14] = "Physical Address Byte 4 Register",
    [0x15] = "Physical Address Byte 5 Register",
    [0x16] = "Multicast Address Byte 0 Register",
    [0x17] = "Multicast Address Byte 1 Register",
    [0x18] = "Multicast Address Byte 2 Register",
    [0x19] = "Multicast Address Byte 3 Register",
    [0x1a] = "Multicast Address Byte 4 Register",
    [0x1b] = "Multicast Address Byte 5 Register",
    [0x1c] = "Multicast Address Byte 6 Register",
    [0x1d] = "Multicast Address Byte 7 Register",
    [0x1e] = "General Purpose Control Register",
    [0x1f] = "General Purpose Register",
    [0x20] = "TX SRAM Write Pointer Address Register Low",
    [0x21] = "TX SRAM Write Pointer Address Register High",
    [0x22] = "TX SRAM Read Pointer Address Register Low",
    [0x23] = "TX SRAM Read Pointer Address Register High",
    [0x24] = "RX SRAM Write Pointer Address Register Low",
    [0x25] = "RX SRAM Write Pointer Address Register High",
    [0x26] = "RX SRAM Read Pointer Address Register Low",
    [0x27] = "RX SRAM Read Pointer Address Register High",
    [0x28] = "Vendor ID Register Low [DM9620]",
    [0x29] = "Vendor ID Register High [DM9620]",
    [0x2a] = "Product ID Register Low",
    [0x2b] = "Product ID Register High",
    [0x2c] = "Chip Revision Register",
    [0x2d] = "TX Special Control Register [DM9620]",
    [0x2e] = "External PHY Force Mode Control Register [DM9620]",
    [0x31] = "Transmit Check Sum Control Register [DM9620]",
    [0x32] = "Receive Check Sum Control Register [DM9620]",
    [0x33] = "External PHY Address Register [DM9620]",
    [0x34] = "General Purpose Control Register 2 [DM9620]",
    [0x35] = "General Purpose Register 2 [DM9620]",
    [0x36] = "General Purpose Control Register 3 [DM9620]",
    [0x37] = "General Purpose Register 3 [DM9620]",
    [0x3a] = "EEPROM and PHY Control Register [DM9620]",
    [0x3d] = "Pause Packet Control/Status Register [DM9620]",
    [0x81] = "Transmit Packet Counter [DM9620]",
    [0x82] = "USB Packet Error Counter [DM9620]",
    [0x83] = "Ethernet Receive Packet CRC Error Counter [DM9620]",
    [0x84] = "Ethernet Transmit Excessive Collision Counter [DM9620]",
    [0x85] = "Ethernet Transmit Collision Counter [DM9620]",
    [0x86] = "Ethernet Transmit Late Collision Counter [DM9620]",
    [0x91] = "RX Header Control/Status Register [DM9620]",
    [0x95] = "USB Squelch Control Register [DM9620]",
    [0x96] = "USB Address Register [DM9620]",
    [0xf0] = "USB Device Address Register",
    [0xf1] = "Receive Packet Counter Register",
    [0xf2] = "Transmit Packet Counter Register/USB Status Register",
    [0xf4] = "USB Control Register",
}


p_dm9601.fields.operation  = ProtoField.uint8("dm9601.op", "Operation", base.HEX, operations)
p_dm9601.fields.regoffset  = ProtoField.uint8("dm9601.regoffset", "RegOffset", base.HEX, regs)
p_dm9601.fields.bc  = ProtoField.uint8("dm9601.bc", "BC", base.HEX)
p_dm9601.fields.data  = ProtoField.uint8("dm9601.data", "Data", base.HEX)
-- Network Control Register
p_dm9601.fields.ncr  = ProtoField.uint8("dm9601.ncr", "Network Control Register", base.HEX)
p_dm9601.fields.ext_phy = ProtoField.uint8("dm9601.ncr.ext_phy", "EXT_PHY", base.HEX, {[0]="Internal PHY", [1]="External PHY"}, 0x80)
p_dm9601.fields.wakeen = ProtoField.uint8("dm9601.ncr.wakeen", "WAKEEN", base.HEX, {[0]="Wakeup disable", [1]="Wakeup enable"}, 0x40)
p_dm9601.fields.reserved = ProtoField.uint8("dm9601.ncr.reserved", "RESERVED", base.HEX, {[0]="Reserved", [1]="Invalid"}, 0x20)
p_dm9601.fields.fcol = ProtoField.uint8("dm9601.ncr.fcol", "FCOL", base.HEX, {[0]="No force collision", [1]="Force collision mode"}, 0x10)
p_dm9601.fields.fdx = ProtoField.uint8("dm9601.ncr.fdx", "FDX", base.HEX, {[0]="No Full-Duplex", [1]="Full-Duplex mode"}, 0x08)
p_dm9601.fields.lbk = ProtoField.uint8("dm9601.ncr.lbk", "LBK", base.HEX, {[0]="normal", [1]="MAC internal loopback", [2]="internal PHY digital loopback", [3]="internal PHY analog loopback"}, 0x06)
p_dm9601.fields.rst = ProtoField.uint8("dm9601.ncr.rst", "RST", base.HEX, {[0]="No", [1]="Software Reset"}, 0x01)
-- EEPROM & PHY Control Register
p_dm9601.fields.epc  = ProtoField.uint8("dm9601.epc", "EEPROM & PHY Control Register", base.HEX)
p_dm9601.fields.no_eep = ProtoField.uint8("dm9601.epc.no_eep", "NO_EEP", base.HEX, {[0]="EEPROM detected", [1]="No EEPROM"}, 0x80)
p_dm9601.fields.ee_type = ProtoField.uint8("dm9601.epc.ee_type", "EE_TYPE", base.HEX, {[0]="93C46", [1]="93C56/66"}, 0x40)
p_dm9601.fields.reep = ProtoField.uint8("dm9601.epc.reep", "REEP", base.HEX, {[0]="No EEPROM reload", [1]="Reload EEPROM"}, 0x20)
p_dm9601.fields.wep = ProtoField.uint8("dm9601.epc.wep", "WEP", base.HEX, {[0]="EEPROM write disable", [1]="EEPROM write enable"}, 0x10)
p_dm9601.fields.epos = ProtoField.uint8("dm9601.epc.epos", "EPOS", base.HEX, {[0]="EEPROM operation", [1]="PHY operation"}, 0x08)
p_dm9601.fields.erprr = ProtoField.uint8("dm9601.epc.erprr", "ERPRR", base.HEX, {[0]="No EEPROM/PHY read initiated", [1]="EEPROM/PHY read initiated"}, 0x04)
p_dm9601.fields.erprw = ProtoField.uint8("dm9601.epc.erprw", "ERPRW", base.HEX, {[0]="No EEPROM/PHY write initiated", [1]="EEPROM/PHY write initiated"}, 0x02)
p_dm9601.fields.erre = ProtoField.uint8("dm9601.epc.erre", "ERRE", base.HEX, {[0]="No EEPROM/PHY access in progress", [1]="EEPROM/PHY access in progress"}, 0x01)
-- EEPROM & PHY Address Register
p_dm9601.fields.epa  = ProtoField.uint8("dm9601.epa", "EEPROM & PHY Address Register", base.HEX)
p_dm9601.fields.phy_adr = ProtoField.uint8("dm9601.epa.phy_adr", "PHY_ADR", base.HEX, {}, 0xc0)
p_dm9601.fields.eroa = ProtoField.uint8("dm9601.epa.eroa", "EEPROM word address", base.HEX, {}, 0x3f)
-- EEPROM & PHY Data Register
p_dm9601.fields.epd  = ProtoField.uint8("dm9601.epd", "EEPROM & PHY Data Register", base.HEX)
-- General Purpose Control Register
p_dm9601.fields.gpcr  = ProtoField.uint8("dm9601.gpcr", "General Purpose Control Register", base.HEX)
p_dm9601.fields.reserved1 = ProtoField.uint8("dm9601.gpcr.reserved", "RESERVED", base.HEX, {[0]="Reserved", [1]="Invalid"}, 0x80)
p_dm9601.fields.gepio6dir = ProtoField.uint8("dm9601.gpcr.gepio6dir", "GEPIO6 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x40)
p_dm9601.fields.gepio5dir = ProtoField.uint8("dm9601.gpcr.gepio5dir", "GEPIO5 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x20)
p_dm9601.fields.gepio4dir = ProtoField.uint8("dm9601.gpcr.gepio4dir", "GEPIO4 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x10)
p_dm9601.fields.gepio3dir = ProtoField.uint8("dm9601.gpcr.gepio3dir", "GEPIO3 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x08)
p_dm9601.fields.gepio2dir = ProtoField.uint8("dm9601.gpcr.gepio2dir", "GEPIO2 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x04)
p_dm9601.fields.gepio1dir = ProtoField.uint8("dm9601.gpcr.gepio1dir", "GEPIO1 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x02)
p_dm9601.fields.gepio0dir = ProtoField.uint8("dm9601.gpcr.gepio0dir", "GEPIO0 direction", base.HEX, {[0]="Input", [1]="Output"}, 0x01)
-- General Purpose Register
p_dm9601.fields.gpr  = ProtoField.uint8("dm9601.gpr", "General Purpose Register", base.HEX)
p_dm9601.fields.gepio6 = ProtoField.uint8("dm9601.ncr.gpr.gepio6", "GEPIO6", base.HEX, {[0]="GEPIO6=0", [1]="GEPIO6=1"}, 0x40)
p_dm9601.fields.gepio5 = ProtoField.uint8("dm9601.ncr.gpr.gepio5", "GEPIO5", base.HEX, {[0]="GEPIO5=0", [1]="GEPIO5=1"}, 0x20)
p_dm9601.fields.gepio4 = ProtoField.uint8("dm9601.ncr.gpr.gepio4", "GEPIO4", base.HEX, {[0]="GEPIO4=0", [1]="GEPIO4=1"}, 0x10)
p_dm9601.fields.gepio3 = ProtoField.uint8("dm9601.ncr.gpr.gepio3", "GEPIO3", base.HEX, {[0]="GEPIO3=0", [1]="GEPIO3=1"}, 0x08)
p_dm9601.fields.gepio2 = ProtoField.uint8("dm9601.ncr.gpr.gepio2", "GEPIO2", base.HEX, {[0]="GEPIO2=0", [1]="GEPIO2=1"}, 0x04)
p_dm9601.fields.gepio1 = ProtoField.uint8("dm9601.ncr.gpr.gepio1", "GEPIO1", base.HEX, {[0]="GEPIO1=0", [1]="GEPIO1=1"}, 0x02)
p_dm9601.fields.gepio0 = ProtoField.uint8("dm9601.ncr.gpr.gepio0", "GEPIO0", base.HEX, {[0]="GEPIO0=0", [1]="GEPIO0=1"}, 0x01)

-- DM9601 IRQ fields
p_dm9601_irq.fields.nsr  = ProtoField.uint8("dm9601_irq.nsr", "Network Status Register", base.HEX)
p_dm9601_irq.fields.tsr1  = ProtoField.uint8("dm9601_irq.tsr1", "Reserved", base.HEX)
p_dm9601_irq.fields.tsr2  = ProtoField.uint8("dm9601_irq.tsr2", "Reserved", base.HEX)
p_dm9601_irq.fields.rsr  = ProtoField.uint8("dm9601_irq.rsr", "RX Status Register", base.HEX)
p_dm9601_irq.fields.rocr  = ProtoField.uint8("dm9601_irq.rocr", "Received Overflow Counter Register", base.HEX)
p_dm9601_irq.fields.rxc  = ProtoField.uint8("dm9601_irq.rxc", "Received Packet Register", base.HEX)
p_dm9601_irq.fields.txc  = ProtoField.uint8("dm9601_irq.txc", "Transmit Packet Register", base.HEX)
p_dm9601_irq.fields.gpr  = ProtoField.uint8("dm9601_irq.gpr", "Reserved", base.HEX)

-- Referenced USB dissector fields.
local f_pid = Field.new("usbll.pid")
local f_bmRequestType = Field.new("usb.bmRequestType")
local f_frame_number = Field.new("frame.number")
local f_request_in = Field.new("usb.request_in")
local f_usb_src = Field.new("usb.src")
local f_usb_dst = Field.new("usb.dst")

local frame2reg = {}

local function network_control_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local ncr_tree = subtree:add(p_dm9601.fields.ncr, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.ext_phy, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.wakeen, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.reserved, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.fcol, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.fdx, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.lbk, tvb(0,1), Data)
  ncr_tree:add(p_dm9601.fields.rst, tvb(0,1), Data)
end

local function eeprom_phy_control_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local epc_tree = subtree:add(p_dm9601.fields.epc, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.no_eep, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.ee_type, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.reep, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.wep, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.epos, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.erprr, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.erprw, tvb(0,1), Data)
  epc_tree:add(p_dm9601.fields.erre, tvb(0,1), Data)
end

local function eeprom_phy_address_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local epa_tree = subtree:add(p_dm9601.fields.epa, tvb(0,1), Data)
  epa_tree:add(p_dm9601.fields.phy_adr, tvb(0,1), Data)
  epa_tree:add(p_dm9601.fields.eroa, tvb(0,1), Data)
end

local function eeprom_phy_data_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local epd_tree = subtree:add(p_dm9601.fields.epd, tvb(0,1), Data)
end

local function general_purpose_control_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local gpcr_tree = subtree:add(p_dm9601.fields.gpcr, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.reserved1, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio6dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio5dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio4dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio3dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio2dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio1dir, tvb(0,1), Data)
  gpcr_tree:add(p_dm9601.fields.gepio0dir, tvb(0,1), Data)
end

local function general_purpose_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local gpr_tree = subtree:add(p_dm9601.fields.gpr, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio6, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio5, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio4, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio3, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio2, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio1, tvb(0,1), Data)
  gpr_tree:add(p_dm9601.fields.gepio0, tvb(0,1), Data)
end

local function x_register_dissector(tvb, pinfo, subtree, op)
  local RegOffset = tonumber(tostring(tvb(3,1)), 16)
  local BC = tonumber(tostring(tvb(5,1)), 16)
  subtree:add(p_dm9601.fields.regoffset, tvb(3,1), RegOffset)
  subtree:add(p_dm9601.fields.bc, tvb(5,1), BC)

  -- translate operation name
  if op == 'WRITE_REGISTER()' then
    op = 'Write'
    pinfo.cols.info = op..' '..regs[RegOffset]
  elseif op == 'READ_REGISTER()' then
      op = 'Read'
  end
  -- ensure register is known and set info column
  if regs[RegOffset] ~= nil then
    pinfo.cols.info = op..' '..regs[RegOffset]
  else
    pinfo.cols.info = op..' '..RegOffset
  end

  -- save register for response dissector
  local frame_number = tonumber(tostring(f_frame_number()))
  frame2reg[frame_number] = RegOffset
end

local function write1_register_dissector(tvb, pinfo, subtree)
  local Data = tonumber(tostring(tvb(1,1)), 16)
  local RegOffset = tonumber(tostring(tvb(3,1)), 16)
  local BC = tonumber(tostring(tvb(5,1)), 16)
  local register_tree = subtree:add(p_dm9601.fields.data, tvb(1,1), Data)
  subtree:add(p_dm9601.fields.regoffset, tvb(3,1), RegOffset)
  subtree:add(p_dm9601.fields.bc, tvb(5,1), BC)
  if regs[RegOffset] ~= nil then
    pinfo.cols.info = 'Write1 '..regs[RegOffset]
  else
    pinfo.cols.info = 'Write1 '..RegOffset
  end

  -- dissect register if known
  if RegOffset == 0x00 then
    network_control_register_dissector(tvb(1,1), pinfo, register_tree)
  elseif RegOffset == 0x0b then
    eeprom_phy_control_register_dissector(tvb(1,1), pinfo, register_tree)
  elseif RegOffset == 0x0c then
    eeprom_phy_address_register_dissector(tvb(1,1), pinfo, register_tree)
  elseif RegOffset == 0x1e then
    general_purpose_control_register_dissector(tvb(1,1), pinfo, register_tree)
  elseif RegOffset == 0x1f then
    general_purpose_register_dissector(tvb(1,1), pinfo, register_tree)
  end
end

local function register_read_response_dissector(tvb, pinfo, subtree, RegOffset)
  local Data = tonumber(tostring(tvb(0,1)), 16)
  local register_tree = subtree:add(p_dm9601.fields.data, tvb(0,1), Data)
  if RegOffset == 0x00 then
    network_control_register_dissector(tvb(0,1), pinfo, register_tree)
  elseif RegOffset == 0x0b then
    eeprom_phy_control_register_dissector(tvb(0,1), pinfo, register_tree)
  elseif RegOffset == 0x0d then
    eeprom_phy_data_register_dissector(tvb(0,1), pinfo, register_tree)
  elseif RegOffset == 0x1f then
    general_purpose_register_dissector(tvb(0,1), pinfo, register_tree)
  end
end

-- Take USB address in form <bus>.<dev>.<endpoint> and extract endpoint
local function addr2endpoint(addr)
  addr = tostring(addr) -- usually we get FieldInfo, which gmatch is not happy about
  for e in addr:gmatch('[.][^.]+') do r=e end
  return r:sub(2)
end

-- dissect interrupt packet (Endpoint 3)
local function interrupt_dissector(tvb, pinfo, subtree, RegOffset)
    local NSR = tonumber(tostring(tvb(0,1)), 16)
    local nsr = subtree:add(p_dm9601_irq.fields.nsr, tvb(0,1), NSR)

    local TSR1 = tonumber(tostring(tvb(1,1)), 16)
    local tsr1 = subtree:add(p_dm9601_irq.fields.tsr1, tvb(1,1), TSR1)

    local TSR2 = tonumber(tostring(tvb(2,1)), 16)
    local tsr2 = subtree:add(p_dm9601_irq.fields.tsr2, tvb(2,1), TSR2)

    local RSR = tonumber(tostring(tvb(3,1)), 16)
    local rsr = subtree:add(p_dm9601_irq.fields.rsr, tvb(3,1), RSR)

    local ROCR = tonumber(tostring(tvb(4,1)), 16)
    local rocr = subtree:add(p_dm9601_irq.fields.rocr, tvb(4,1), ROCR)

    local RXC = tonumber(tostring(tvb(5,1)), 16)
    local rxc = subtree:add(p_dm9601_irq.fields.rxc, tvb(5,1), RXC)

    local TXC = tonumber(tostring(tvb(6,1)), 16)
    local txc = subtree:add(p_dm9601_irq.fields.txc, tvb(6,1), TXC)

    local GPR = tonumber(tostring(tvb(7,1)), 16)
    local gpr = subtree:add(p_dm9601_irq.fields.gpr, tvb(7,1), GPR)
end

-- Main DM9601 dissector function.
function p_dm9601.dissector(tvb, pinfo, tree)
    -- get usbll.pid
    local err, result = pcall(function () return tonumber(tostring(f_pid())) end)
    local pid = 'Error'
    if err == false then
      -- in usbmon pcaps there is no USBLL
      -- FIXME: what about data packets?
      pid = 0xc3
    else
      pid = result
    end
    local usb_src = f_usb_src()
    local usb_dst = f_usb_dst()
    src_ep = addr2endpoint(usb_src)
    dst_ep = addr2endpoint(usb_dst)
    if src_ep == '1' or dst_ep == '1' then
      pinfo.cols.protocol = 'EthIn'
      return
    end
    if src_ep == '2' or dst_ep == '2' then
      pinfo.cols.protocol = 'EthOut'
      return
    end
    if src_ep == '3' or dst_ep == '3' then
      pinfo.cols.protocol = p_dm9601.name..' IRQ'
      local subtree = tree:add(p_dm9601_irq, tvb(0,8), "DM9601 IRQ")
      interrupt_dissector(tvb, pinfo, subtree)
      return
    end
		if pid == 0xc3 then -- SETUP DATA0
      pinfo.cols.protocol = p_dm9601.name
      local bmRequestType = tonumber(tostring(f_bmRequestType()))
      local subtree = tree:add(p_dm9601, tvb(), "DM9601")
      local bRequest = tonumber(tostring(tvb(0,1)))
      local op = bit.bor(bit.lshift(bmRequestType, 8), bRequest)
      --if bmRequestType == 0xc0 and bRequest == 0x00 then -- READ_REGISTER()
      if operations[op] ~= nil then
        subtree:add(p_dm9601.fields.operation, tvb(0,1), op)
        pinfo.cols.info = operations[op]
      end
      if operations[op] == 'READ_REGISTER()' or operations[op] == 'WRITE_REGISTER()' then
        x_register_dissector(tvb, pinfo, subtree, operations[op])
      elseif operations[op] == 'WRITE1_REGISTER()' then
        write1_register_dissector(tvb, pinfo, subtree)
      end
    elseif pid == 0x4b and f_usb_src() ~= "host" then
      -- TODO: catch reassembled requests!!!
      local subtree = tree:add(p_dm9601, tvb(), "DM9601")
      pinfo.cols.protocol = p_dm9601.name
      local request_in = f_request_in()
      pinfo.cols.info = 'Read Response'
      local err, result = pcall(function () return tonumber(tostring(request_in)) end)
      if err == false then
        err = result
        return 0
      end
      request_in = result
      local request_reg = frame2reg[request_in]
      if regs[request_reg] ~= nil then
        pinfo.cols.info = regs[request_reg]..' Response'
      else
        pinfo.cols.info = request_reg..' Response'
      end
      register_read_response_dissector(tvb, pinfo, subtree, request_reg)
    end
    return 0
end

-- Register DM9601 protocol dissector during initialization.
function p_dm9601.init()
    local usb_product_dissectors = DissectorTable.get("usb.product")

    usb_product_dissectors:add(0x0fe68101, p_dm9601) -- DM9601 USB to Fast Ethernet Adapter
    usb_product_dissectors:add(0x0fe69700, p_dm9601) -- DM9601 USB to Fast Ethernet Adapter

    local usb_bulk_dissectors = DissectorTable.get("usb.bulk")
end