'----------------------------------------------------------------------------------
' Embedded UDP&WebServer   -   Atmega32 and RTL8019AS    -   Embedded UDP&WebServer
'----------------------------------------------------------------------------------
'
' Version 1 - April 1 2005 - Ben Zijlstra - Netherlands - https://benshobbycorner.nl/bzijlstra


$crystal = 7372800
$regfile = "M32def.dat"
$baud = 57600

Declare Sub Write_rtl8019as(byval Regaddr As Byte , Byval Regdata As Byte)
Declare Sub Read_rtl8019as(byval Regaddr As Byte)
Declare Sub Init_rtl8019as
'Declare Sub Showregs
Declare Sub Getpacket
Declare Sub Overrun
Declare Sub Arp
Declare Sub Udp
Declare Sub Icmp
Declare Sub Icmp_checksum
Declare Sub Tcp
Declare Sub Write_dest_mac
Declare Sub Packetshape
Declare Sub Echopacket
Declare Sub Setipaddrs
Declare Sub Ip_header_checksum

Dim Myip(4) As Byte At &H64
Dim My_ip As Long At &H64 Overlay

Dim Regaddr As Byte
Dim Regdata As Byte
'Ethernet header layout
Dim Hdr_chksum As Long
Dim Byte_read As Byte
Dim Hulp1 As Byte
Dim Mymac(6) As Byte
Dim I As Integer
Dim Rxlen As Word
Dim Hulp2 As Word
Dim Hulp3 As Word
Dim Hulp4 As Byte
Dim Data_l As Byte
Dim Data_h As Byte
'RTL8019AS
Dim Txstart As Byte
Dim Txlen As Word

Dim I_header_length As Word
Dim I_odd As Byte
Dim I_chksum32 As Long
Dim Hulp6 As Word At &HAF
Dim Hulp6h As Byte At &HB0 Overlay
Dim Hulp6l As Byte At &HAF Overlay
Dim I_x As Word
Dim I_hulp1 As Word
Dim I_checksum16 As Word
Dim I_temp16 As Word

Dim I_value16 As Word At &HB1
Dim I_value16h As Byte At &HB2 Overlay
Dim I_value16l As Byte At &HB1 Overlay

Dim Ip_value16 As Word At &HB3
Dim Ip_value16h As Byte At &HB4 Overlay
Dim Ip_value16l As Byte At &HB3 Overlay

Dim Result16 As Word At &HB5
Dim Result16h As Byte At &HB6 Overlay
Dim Result16l As Byte At &HB5 Overlay

'variables with overlays
Dim Pageheader(4) As Byte At &HAB
Dim T_enetpacketlenl As Byte At &HAD Overlay
Dim T_enetpacketlenh As Byte At &HAE Overlay
Dim Resend As Byte
Dim T As Byte

Dim Packet(1500) As Byte At &HC0
'Ethernet packet destination
Dim T_enetpacketdest0 As Byte At &HC0 Overlay
Dim T_enetpacketdest1 As Byte At &HC1 Overlay
Dim T_enetpacketdest2 As Byte At &HC2 Overlay
Dim T_enetpacketdest3 As Byte At &HC3 Overlay
Dim T_enetpacketdest4 As Byte At &HC4 Overlay
Dim T_enetpacketdest5 As Byte At &HC5 Overlay
'Ethernet packet source
Dim T_enetpacketsrc0 As Byte At &HC6 Overlay
Dim T_enetpacketsrc1 As Byte At &HC7 Overlay
Dim T_enetpacketsrc2 As Byte At &HC8 Overlay
Dim T_enetpacketsrc3 As Byte At &HC9 Overlay
Dim T_enetpacketsrc4 As Byte At &HCA Overlay
Dim T_enetpacketsrc5 As Byte At &HCB Overlay
'Ethernet packet type
Dim T_enetpackettype As Word At &HCC Overlay
Dim T_arp_hwtype1 As Byte At &HCF Overlay
'Arp
Dim T_arp_prttype1 As Byte At &HD1 Overlay
Dim T_arp_hwlen As Byte At &HD2 Overlay
Dim T_arp_prlen As Byte At &HD3 Overlay
Dim T_arp_op1 As Byte At &HD5 Overlay
'arp source ip address
Dim T_arp_sipaddr0 As Byte At &HDC Overlay
Dim T_arp_sipaddr1 As Byte At &HDD Overlay
Dim T_arp_sipaddr2 As Byte At &HDE Overlay
Dim T_arp_sipaddr3 As Byte At &HDF Overlay
'arp target IP address
Dim T_arp_tipaddr As Long At &HE6 Overlay
'IP header layout IP version and header length
Dim T_ip_vers_len As Byte At &HCE Overlay
'packet length
Dim T_ip_pktlen0 As Byte At &HD0 Overlay
Dim T_ip_pktlen1 As Byte At &HD1 Overlay
'protocol (ICMP=1, TCP=6, UDP=11)
Dim T_ip_proto As Byte At &HD7 Overlay
'header checksum
Dim T_ip_hdr_cksum0 As Byte At &HD8 Overlay
Dim T_ip_hdr_cksum1 As Byte At &HD9 Overlay
Dim T_ip_hdr_cksum As Word At &HD8 Overlay
'IP address of source
Dim T_ip_srcaddr0 As Byte At &HDA Overlay
Dim T_ip_srcaddr1 As Byte At &HDB Overlay
Dim T_ip_srcaddr2 As Byte At &HDC Overlay
Dim T_ip_srcaddr3 As Byte At &HDD Overlay
Dim T_ip_srcaddr As Long At &HDA Overlay
'IP address of destination
Dim T_ip_destaddr0 As Byte At &HDE Overlay
Dim T_ip_destaddr1 As Byte At &HDF Overlay
Dim T_ip_destaddr2 As Byte At &HE0 Overlay
Dim T_ip_destaddr3 As Byte At &HE1 Overlay
Dim T_ip_destaddr As Long At &HDE Overlay
Dim T_icmp_type As Byte At &HE2 Overlay
Dim T_icmp_code As Byte At &HE3 Overlay
Dim T_icmp_cksum0 As Byte At &HE4 Overlay
Dim T_icmp_cksum1 As Byte At &HE5 Overlay
Dim T_icmp_cksum As Word At &HE4 Overlay
Dim Tcp_srcporth As Byte At &HE2 Overlay
Dim Tcp_srcportl As Byte At &HE3 Overlay
Dim Tcp_destporth As Byte At &HE4 Overlay
Dim Tcp_destportl As Byte At &HE5 Overlay
Dim Tcp_seqnum3 As Byte At &HE6 Overlay
Dim Tcp_seqnum2 As Byte At &HE7 Overlay
Dim Tcp_seqnum1 As Byte At &HE8 Overlay
Dim Tcp_seqnum0 As Byte At &HE9 Overlay
Dim Tcp_acknum3 As Byte At &HEA Overlay
Dim Tcp_acknum2 As Byte At &HEB Overlay
Dim Tcp_acknum1 As Byte At &HEC Overlay
Dim Tcp_acknum0 As Byte At &HED Overlay
Dim Tcp_hdr As Byte At &HEE Overlay
Dim Tcp_flags As Byte At &HEF Overlay
Dim Tcp_cksumh As Byte At &HF2 Overlay
Dim Tcp_cksuml As Byte At &HF3 Overlay
Dim Tcp_cksum As Word At &HF2 Overlay
'UDP header
Dim T_udp_srcport0 As Byte At &HE2 Overlay
Dim T_udp_srcport1 As Byte At &HE3 Overlay
Dim T_udp_destport0 As Byte At &HE4 Overlay
Dim T_udp_destport1 As Byte At &HE5 Overlay
Dim T_udp_destport As Word At &HE4 Overlay
Dim T_udp_len0 As Byte At &HE6 Overlay
Dim T_udp_len1 As Byte At &HE7 Overlay
Dim T_udp_chksum0 As Byte At &HE8 Overlay
Dim T_udp_chksum1 As Byte At &HE9 Overlay
Dim T_udp_chksum As Word At &HE8 Overlay
Dim T_udp_data As Byte At &HEA Overlay


Const Debug = 0                                             ' put 1 for debug, 0 for no debug
Const Rstport = &H18
Const Isr = &H07
Const Msg_initfail = "Init failed"
Const Cr = &H00
Const Dcrval = &H58
Const Dcr = &H0E
Const Rbcr0 = &H0A
Const Rbcr1 = &H0B
Const Rcr = &H0C
Const Tpsr = &H04
Const Txtstart = &H40
Const Tcr = &H0D
Const Pstart = &H01
Const Rxstart = &H46
Const Bnry = &H03
Const Pstop = &H02
Const Rxstop = &H60
Const Curr = &H07
Const Imr = &H0F
Const Imrval = &H11
Const Tcrval = &H00
Const Rdmaport = &H10
Const Rsar0 = &H08
Const Rsar1 = &H09
Const Tbcr0 = &H05
Const Tbcr1 = &H06

'IP protocol types
'icmp
Const Prot_icmp = &H01
'tcp
Const Prot_tcp = &H06
'udp
Const Prot_udp = &H11


'RTL8019AS ISR Register definitions
Const Rdc = &H40

Config Int0 = Rising

Mymac(1) = &H00
Mymac(2) = &H10
Mymac(3) = &H20
Mymac(4) = &H30
Mymac(5) = &H40
Mymac(6) = &H50

Myip(1) = 192
Myip(2) = 168
Myip(3) = 0
Myip(4) = 100

#if Debug = 1
Print "Hello world"
#endif

Databus Alias Porta
_databus Alias Pina
Rtldata Alias Porta
Databus_ddr Alias Ddra

Addrbus Alias Portb
Addrbus_ddr Alias Ddrb

Resetport Alias Portd
Eeprom Alias Portd
Ior_pin Alias Portd.6
Iow_pin Alias Portd.7
Resetport_ddr Alias Ddrd

Inputport1 Alias Pinc
Inputport2 Alias Portc

Latch Alias Portd.3
Resetport_ddr = &HF8                                        ' leave RXD and TXD

Call Init_rtl8019as
'Call Showregs
'Stop

Enable Interrupts
Enable Int0
On Int0 Rtl8019as_interrupt
'start the NIC
Call Write_rtl8019as(cr , &H22)
Do
Loop
End


' Routine to handle an interrupt on the RTL8019AS
'
Rtl8019as_interrupt:
   #if Debug = 1
      Print "Interrupt from RTL8019as"
   #endif
   Disable Int0
   'read the interrupt status register
   Call Read_rtl8019as(isr)
   'if the receive buffer has been overrun
   If Byte_read.4 = 1 Then
      Call Overrun
   End If
   'if the receive buffer holds a good packet
   If Byte_read.0 = 1 Then
      Call Getpacket
   End If
   'make sure the receive buffer ring is empty. If BNRY = CURR, the buffer is empty
   Call Read_rtl8019as(bnry)
   Data_l = Byte_read
   Call Write_rtl8019as(cr , &H62)
   Call Read_rtl8019as(curr)
   Data_h = Byte_read
   Call Write_rtl8019as(cr , &H22)
   'buffer is not empty, get next packet
   If Data_l <> Data_h Then
      Call Getpacket
   End If
   'reset the interrupts bits
   Call Write_rtl8019as(isr , &HFF)
   Call Write_rtl8019as(cr , &H22)
   Enable Int0
Return


' Routine to Write to NIC Control register
'
Sub Write_rtl8019as(regaddr , Regdata)
   Addrbus = Regaddr
   Databus = Regdata
   Databus_ddr = &HFF
   nop
   Reset Iow_pin
   nop
   Set Iow_pin
   nop
   Databus_ddr = &H00
   Databus = &HFF
End Sub


' Routine to read from NIC Control register
'
Sub Read_rtl8019as(regaddr)
   Databus_ddr = &H00
   Databus = &HFF
   Addrbus = Regaddr
   Reset Ior_pin
   nop
   Byte_read = Pina
   nop
   Set Ior_pin
   nop
End Sub


' Routine to initialise the RTL8019AS ethernetchip
'
Sub Init_rtl8019as
Databus_ddr = &H00
Databus = &HFF
Addrbus_ddr = &HFF
Addrbus = &H00
Resetport_ddr = &HF8
Reset Eeprom.5
Set Iow_pin
Set Ior_pin
Set Resetport.4
Waitms 2
Reset Resetport.4
Call Read_rtl8019as(rstport)
Call Write_rtl8019as(rstport , Byte_read)
Waitms 10
'check for good soft reset
Call Read_rtl8019as(isr)
If Byte_read.7 = 0 Then
      Print Msg_initfail
End If
Call Write_rtl8019as(cr , &H21)
Waitms 2
Call Write_rtl8019as(dcr , Dcrval)
Call Write_rtl8019as(rbcr0 , &H00)
Call Write_rtl8019as(rbcr1 , &H00)
Call Write_rtl8019as(rcr , &H04)
Call Write_rtl8019as(tpsr , Txtstart)
Call Write_rtl8019as(tcr , &H02)
Call Write_rtl8019as(pstart , Rxstart)
Call Write_rtl8019as(bnry , Rxstart)
Call Write_rtl8019as(pstop , Rxstop)
Call Write_rtl8019as(cr , &H61)
Waitms 2
Call Write_rtl8019as(curr , Rxstart)
For Hulp1 = 1 To 6
     Call Write_rtl8019as(hulp1 , Mymac(hulp1))
Next Hulp1
Call Write_rtl8019as(cr , &H21)
Call Write_rtl8019as(dcr , Dcrval)
Call Write_rtl8019as(cr , &H22)
Call Write_rtl8019as(isr , &HFF)
Call Write_rtl8019as(imr , Imrval)
Call Write_rtl8019as(tcr , Tcrval)
End Sub


'(
' Routine show the contents of the RTL8019as registers
'
Sub Showregs
Local Cntr1 As Byte
Local Cntr2 As Byte
Call Write_rtl8019as(cr , &H21)
Print
Print "Realtek 8019AS Register dump"
Print
Print "REG  Page0 Page1 Page2 Page3"
Print
For Cntr1 = 0 To 15
   Cntr2 = Cntr1
   Print Hex(cntr2);
   Print "    ";
   Call Write_rtl8019as(cr , &H21)
   Cntr2 = Cntr1
   Call Read_rtl8019as(cntr2)
   Print Hex(byte_read);
   Print "    ";
   Call Write_rtl8019as(cr , &H61)
   Cntr2 = Cntr1
   Call Read_rtl8019as(cntr2)
   Print Hex(byte_read);
   Print "    ";
   Call Write_rtl8019as(cr , &HA1)
   Cntr2 = Cntr1
   Call Read_rtl8019as(cntr2)
   Print Hex(byte_read);
   Print "    ";
   Call Write_rtl8019as(cr , &HE1)
   Cntr2 = Cntr1
   Call Read_rtl8019as(cntr2)
   Print Hex(byte_read)
Next Cntr1
End Sub
')


Sub Overrun
   Call Read_rtl8019as(cr)
   Data_l = Byte_read
   Call Write_rtl8019as(cr , &H21)
   Waitms 2
   Call Write_rtl8019as(rbcr0 , &H00)
   Call Write_rtl8019as(rbcr1 , &H00)
   Hulp1 = Data_l And &H04
   If Hulp1 <> 0 Then
      Resend = 0
      Else
         If Hulp1 = 0 Then
            Call Read_rtl8019as(isr)
            Data_l = Byte_read
            Hulp1 = Data_l And &H02
            Hulp4 = Data_l And &H08
            Hulp3 = Hulp1 Or Hulp4
               If Hulp3 > 0 Then
                  Resend = 0
                  Else
                  Resend = 1
               End If
         End If
   End If
   Call Write_rtl8019as(tcr , &H02)
   Call Write_rtl8019as(cr , &H22)
   Call Write_rtl8019as(bnry , Rxstart)
   Call Write_rtl8019as(cr , &H62)
   Call Write_rtl8019as(curr , Rxstart)
   Call Write_rtl8019as(cr , &H22)
   Call Write_rtl8019as(isr , &H10)
   Call Write_rtl8019as(tcr , Tcrval)
End Sub


' Routine to execute send packet command to retrieve the packet
'
Sub Getpacket
   Call Write_rtl8019as(cr , &H1A)
   For I = 0 To 4
      Call Read_rtl8019as(rdmaport)
      Pageheader(i + 1) = Byte_read
   Next I
   'watch it. overlay variables
   Result16h = T_enetpacketlenh
   Result16l = T_enetpacketlenl
   Rxlen = Result16
   Hulp2 = Rxlen + 1
   For I = 1 To Hulp2
      Call Read_rtl8019as(rdmaport)
      'dump any bytes that will overrun the receive buffer
      If I < 1500 Then
         Packet(i + 1) = Byte_read
      End If
   Next I
   Hulp1 = Byte_read And Rdc
   If Hulp1 <> 64 Then
      Call Read_rtl8019as(isr)
   End If

   Call Write_rtl8019as(isr , &HFF)


   ' Routine to process an ARP packet
   '
   If T_enetpackettype = &H0608 Then
      If T_arp_hwtype1 = &H01 Then
         If T_arp_prttype1 = &H00 Then
            If T_arp_hwlen = &H06 Then
               If T_arp_prlen = &H04 Then
                  If T_arp_op1 = &H01 Then
                     If My_ip = T_arp_tipaddr Then
                        Call Arp
                     End If
                  End If
               End If
            End If
         End If
      End If
   End If


   ' Routine to go ahead with icmp or udp
   '
   If T_enetpackettype = &H0008 Then
         If T_ip_destaddr = My_ip Then
            Select Case T_ip_proto
               Case Prot_icmp : Call Icmp
               Case Prot_tcp : Call Tcp
               Case Prot_udp : Call Udp
            End Select
         End If
   End If
End Sub

' Routine to handle ARP-traffic
'
Sub Arp
   'Start the NIC
   Call Write_rtl8019as(cr , &H22)
   'load beginning page for transmit buffer
   Call Write_rtl8019as(tpsr , Txtstart)
   'set start address for remote DMA operation
   Call Write_rtl8019as(rsar0 , &H00)
   Call Write_rtl8019as(rsar1 , &H40)
   'clear the interrupts
   Call Write_rtl8019as(isr , &HFF)
   'load data byte count for remote DMA
   Call Write_rtl8019as(rbcr0 , &H3C)
   Call Write_rtl8019as(rbcr1 , &H00)
   'do remote write operation
   Call Write_rtl8019as(cr , &H12)
   'write destination MAC address
   Call Write_dest_mac
   'write source address
   For I = 1 To 6
       Call Write_rtl8019as(rdmaport , Mymac(i))
   Next I
   'arp target IP address
   'arp_op1 = packet(&h16)
   Packet(&H16) = &H02
   For I = 0 To 9
      Hulp1 = &HCC + I
      T = Peek(hulp1)
      Call Write_rtl8019as(rdmaport , T)
   Next I
   'write ethernet module mac address
   For I = 1 To 6
      Call Write_rtl8019as(rdmaport , Mymac(i))
   Next I
   'write myip
   For I = 1 To 4
      Call Write_rtl8019as(rdmaport , Myip(i))
   Next I
   'write remote mac address
   Call Write_dest_mac
   'write remote IP address
   Call Write_rtl8019as(rdmaport , T_arp_sipaddr0)
   Call Write_rtl8019as(rdmaport , T_arp_sipaddr1)
   Call Write_rtl8019as(rdmaport , T_arp_sipaddr2)
   Call Write_rtl8019as(rdmaport , T_arp_sipaddr3)
  'write som pad characters to fill out the packet to the minimum length
   For I = 0 To &H11
      Call Write_rtl8019as(rdmaport , &H00)
   Next I
   'make sure the DMA operation has succesfully completed
   Byte_read = 0
   Do
      Hulp1 = Byte_read And Rdc
      Call Read_rtl8019as(isr)
   Loop Until Hulp1 = 0
   'load numbers of bytes to be transmitted
   Call Write_rtl8019as(tbcr0 , &H3C)
   Call Write_rtl8019as(tbcr1 , &H00)
   'send the contents of the transmit buffer onto the network
   Call Write_rtl8019as(cr , &H24)
End Sub


Sub Tcp
End Sub

Sub Udp
End Sub

Sub Write_dest_mac
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc0)
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc1)
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc2)
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc3)
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc4)
   Call Write_rtl8019as(rdmaport , T_enetpacketsrc5)
End Sub


Sub Icmp
'set echo reply
T_icmp_type = &H00
T_icmp_code = &H00
'setup the IP-header
Call Setipaddrs
Call Icmp_checksum
Call Echopacket
End Sub



' Routine to handle the source/destination address
'
Sub Setipaddrs
T_ip_destaddr = T_ip_srcaddr
'make ethernet module IP address source address
T_ip_srcaddr = My_ip
Call Packetshape
Call Ip_header_checksum
End Sub


' Routine to echo a complete packet
'

Sub Echopacket
Call Write_rtl8019as(cr , &H22)
Call Write_rtl8019as(tpsr , Txtstart)
Call Write_rtl8019as(rsar0 , &H00)
Call Write_rtl8019as(rsar1 , &H40)
Call Write_rtl8019as(isr , &HFF)
Hulp1 = T_enetpacketlenl - 4
Call Write_rtl8019as(rbcr0 , Hulp1)
Call Write_rtl8019as(rbcr1 , T_enetpacketlenh)
Call Write_rtl8019as(cr , &H12)
Result16h = T_enetpacketlenh

Result16l = T_enetpacketlenl
Result16 = Result16 - 4
Txlen = Result16
'write the complete packet to the RTL8019AS from packet(1) to packet(txlen+1)
Hulp2 = Txlen + 1
For I = 1 To Hulp2
Call Write_rtl8019as(rdmaport , Packet(i))
Next I
Byte_read = 0
While Hulp1 <> 0
Hulp1 = Byte_read And Rdc
Call Read_rtl8019as(isr)
Wend
Hulp1 = T_enetpacketlenl - 4
Call Write_rtl8019as(tbcr0 , Hulp1)
Call Write_rtl8019as(tbcr1 , T_enetpacketlenh)
Call Write_rtl8019as(cr , &H24)
End Sub





Sub Packetshape
'move hardware source address to destination address
T_enetpacketdest0 = T_enetpacketsrc0
T_enetpacketdest1 = T_enetpacketsrc1
T_enetpacketdest2 = T_enetpacketsrc2
T_enetpacketdest3 = T_enetpacketsrc3
T_enetpacketdest4 = T_enetpacketsrc4
T_enetpacketdest5 = T_enetpacketsrc5
' 'Make ethernet module mac address the source address
T_enetpacketsrc0 = Mymac(1)
T_enetpacketsrc1 = Mymac(2)
T_enetpacketsrc2 = Mymac(3)
T_enetpacketsrc3 = Mymac(4)
T_enetpacketsrc4 = Mymac(5)
T_enetpacketsrc5 = Mymac(6)
End Sub



' Routine to calculate a ICMP-checksum
'
Sub Icmp_checksum
   'clear the ICMP checksum
   T_icmp_cksum = &H00
   'calculate the ICMP checksum
   I_header_length = T_ip_pktlen1 - 20
   'I_header_length = I_header_length - 20
   I_odd = I_header_length Mod 2
   '14 for MAC-part
   '20 for IP-header
   'start on 35
   'ip_pktlen = 00 3c (60)
   'icmp-packetlengte = ip_pktlen - ip_header
   I_chksum32 = 0
   'Total packetlength - ip_header - 1
   Hulp6h = T_ip_pktlen0
   Hulp6l = T_ip_pktlen1
   Hulp6 = Hulp6 + 13
   For I_x = 35 To Hulp6 Step 2
      I_value16h = Packet(i_x)
      I_hulp1 = I_x + 1
      I_value16l = Packet(i_hulp1)
      I_value16 = Not I_value16
      I_chksum32 = I_chksum32 + I_value16
   Next I_x
   If I_odd = 1 Then
      I_value16h = Packet(i_x)
      I_value16l = 0
      I_value16 = Not I_value16
      I_chksum32 = I_chksum32 + I_value16
   End If
   I_checksum16 = I_chksum32
   I_temp16 = Highw(i_chksum32)
   I_checksum16 = I_checksum16 + I_temp16
   T_icmp_cksum0 = High(i_checksum16)
   T_icmp_cksum1 = Low(i_checksum16)
End Sub




' Routine to calculate a IP-header checksum
'
Sub Ip_header_checksum
   Local Ip_x As Byte
   Local Ip_hulp1 As Byte
   Local Ip_chksum32 As Long
   Local Ip_checksum16 As Word
   Local Ip_temp16 As Word
   Local Ip_header_length As Byte
   'calculate the IP header checksum
   T_ip_hdr_cksum = &H00
   Hdr_chksum = 0
   Ip_header_length = T_ip_vers_len And &H0F
   Ip_header_length = 4 * Ip_header_length
   Hulp1 = &H0E + Ip_header_length
   Ip_chksum32 = 0
   For Ip_x = 15 To Hulp1 Step 2
      Ip_value16h = Packet(ip_x)
      Ip_hulp1 = Ip_x + 1
      Ip_value16l = Packet(ip_hulp1)
      Ip_value16 = Not Ip_value16
      Ip_chksum32 = Ip_chksum32 + Ip_value16
   Next Ip_x
   Ip_checksum16 = Ip_chksum32
   Ip_temp16 = Highw(ip_chksum32)
   Ip_checksum16 = Ip_checksum16 + Ip_temp16
   T_ip_hdr_cksum0 = High(ip_checksum16)
   T_ip_hdr_cksum1 = Low(ip_checksum16)
End Sub









'' hulp5 is hulp2 geworden