-- declare some Fields to be read
usb_hl_f = Field.new("usb.usbpcap_header_len")
usb_tt_f = Field.new("usb.transfer_type")
usb_dl_f = Field.new("usb.data_len")

-- declare our (pseudo) protocol
dispenser_proto = Proto("dispenser","NCR S1 Dispenser")

u1_vals = {
        [ 1 ] = "Command (?)",
        [ 2 ] = "Upload (?)",
}

-- create the fields for our "protocol"
u00_00_F = ProtoField.uint8("dispenser.u01", "Unknown 00", base.HEX, u1_vals)
u01_07_F = ProtoField.bytes("dispenser.u02", "Unknown 01-07")
magic_F  = ProtoField.uint16("dispenser.magic", "Magic Cookie", base.HEX)
u0a_0f_F = ProtoField.bytes("dispenser.u0a", "Unknown 0a-0f", base.HEX)
u10_17_F = ProtoField.bytes("dispenser.u10", "Unknown 10-17", base.HEX)
u18_1f_F = ProtoField.bytes("dispenser.u18", "Unknown 18-1f", base.HEX)

-- add the field to the protocol
dispenser_proto.fields = {
        u00_00_F,
        u01_07_F,
        magic_F,
        u0a_0f_F,
        u10_17_F,
        u18_1f_F,
}

-- create a function to "postdissect" each frame
function dispenser_proto.dissector(buffer,pinfo,tree)
    -- obtain the current values the protocol fields
    local usb_hl = usb_hl_f()
    local usb_tt = usb_tt_f()
    local usb_dl = usb_dl_f()
    if usb_tt.value == 0x01 and usb_dl.value >= 63 then
        local off = 64
	if usb_hl then
	    off = usb_hl.value
	end
        local magic = buffer(off +  8,2)
        if magic:le_uint() == 0xbeef then
            local subtree = tree:add(dispenser_proto, "NCR S1 Dispenser")
            subtree:add(u00_00_F, buffer(off + 0x00,1))
            subtree:add(u01_07_F, buffer(off + 0x01,7))
            subtree:add_le(magic_F, magic)
            subtree:add(u0a_0f_F, buffer(off + 0x0a,6))
            subtree:add(u10_17_F, buffer(off + 0x10,8))
            subtree:add(u18_1f_F, buffer(off + 0x18,8))
        end
    end
end

-- register our protocol as a postdissector
register_postdissector(dispenser_proto)