CPC/IP - A TCP/IP stack for Amstrad CPCs

CPC/IP is an implementation of the PPP, SLIP, IP, ICMP, UDP, TCP, DNS, TFTP, HTTP, ping, finger and telnet protocols for Amstrad CPC computers with an Amstrad, Pace or CPC Amstrad International serial interface. The code occupies about 14K, excluding the serial, filing system and IP buffers, but including all the clients and servers and their buffers/data.

What's new?

• 2001-06-03 (CPC/IP v0.20)
  CPC/IP makes a comeback! The TCP layer has been radically overhauled to present a proper API, have a proper state machine, and a retransmission timeout. The PPP layer has a workaround for buggy PPP implementations. The telnet client now supports a line mode, including echo suppression; it's quite feasible to use this to send/receive email/news. The serial device driver now supports the CPC Amstrad International serial interface.
• 2000-10-15 (CPC/IP v0.12)
  Improve portability by introducing a standard I/O API (use this in the HTTP server (fixes problem with serving binary files); note the TFTP server has not been updated yet). Extend the Amstrad serial interface device driver to support polling, parity, more stop bits and not using hardware flow control (no hardware flow control is now the default for the executable). Extend the configuration to allow finer control over the components included in the build. Add some hints on starting a port. Tweak head in cpcsutils to support files bigger than 64K.
• 2000-07-02
  Update the Z80 assembler.
• 2000-03-12 (CPC/IP v0.11)
  Improve PPP layer: make more robust against remote rejection, add requesting of DNS server address to use, and add peer PPP tickle (use Copy to send this, immediately after the physical link has been established). Update the Z80 assembler.
• 2000-02-29
  I wanted to release something on this cool date, but unfortunately I was ill. Oh, well...
• 2000-01-23 (CPC/IP v0.10)
  Add support for PPP (but SLIP remains the default for the executable for now). Add support for 64K machines (this is now the default for the executable) in the Amstrad serial interface device driver and loopback driver. The telnet client now reports when the connection has been established (incidentally, you can now enter a bare CR (i.e. not a CRLF) using Enter). Note you'll need to recompile ZMAC 1.1.1.2 with MAXIFS on line 55 #defined to 1024, say, if you want to use that to assemble CPC/IP; I haven't tried assembling CPC/IP with Maxam for quite a while now! Also, the config stuff has moved one byte up (in case you're using a loader to set things like your address and DNS server, or DNS zone, or hosts.txt) and all the config stuff which used to be in main.z is now in config.z.
• 2000-01-01 (CPC/IP v0.09)
  Nothing to report. It's not even clear CPC/IP v0.09 ever existed. Ask ARM about the ARM4 and ARM5 for more details.
• 1999-12-19 (CPC/IP v0.08)
  Add resolver and nameserver lookup client; default nameserver is 127.0.0.1 (localhost). Speed up telnet console output. Add nameserver address and domain name to configuration; the nameserver address can be set with the ifconfig module. A few miscellaneous little bug fixes.
• 1999-11-28 (CPC/IP v0.07, the birthday release!)
  Release tipi, the HTTP/0.9 server. Improve the TCP layer, so it's at least plausible. Improve telnet, in particular so it can function as a console (with a suitable terminfo). There's a hosts.txt-like mechanism, which the clients now use. Add driver for the CPC Amstrad International serial interface, courtesy of Tim RIEMANN. Note the code is now loaded at &3800 with HIMEM at &27ff, CPC/IP's default IP address is now 192.168.6.128, Ctrl-[ should be used to abort a telnet connection, and Ctrl-Esc should be used to quit CPC/IP -- or use the new quit command.
• 1999-10-03
  Update the Z80 assembler.
• 1999-09-09 (CPC/IP v0.06)
  ping and (basic) telnet clients added. Loopback support added. TCP layer still exceedingly rudimentary! ICMP checksums now fully supported. The command-line interface has been extended to support multiple clients.
• 1999-08-08
  Release a mode 2 text accelerator. Tweak the set-up details a bit more.
• 1999-07-18
  Release a Z80 assembler. Improve this document (add more links and more set-up details).
• 1999-07-04
  Fix bug in the screen saver: it wouldn't work with a 464 with a disc interface.
• 1999-06-27 (CPC/IP v0.05)
  Release DNS server.
• 1999-06-20
  Release CPC screen saver and Z80 symbolic disassembler.
• 1999-06-06 (CPC/IP v0.04)
  Forgot head.c in cpcsutils! Minor tab-handling bug fixed. This file added (as documentation) to the zipped sources. Serial device driver optimised.
• 1999-05-31 (CPC/IP v0.03)
  Very rudimentary TCP layer implemented; enough for a finger client. TFTP server now handles AMSDOS errors and reports them remotely. Miscellaneous improvements and bug fixes. A bunch of |BLOW and |SUCK utilities, cpcsutils, and documents on AMSDOS and Amstrad serial interface features.
• 1999-05-03 (CPC/IP v0.02)
  UDP layer and TFTP server (writes only) implemented. Source exploded into multiple files, and made more modular and documented. A couple of bug fixes. This document updated and expanded a bit.
• 1999-04-18 (CPC/IP v0.01)
  It's all new.

Compatibility

CPC/IP is compatible with the following Internet protocols, with the limitations listed further below:

• PPP (RFC1661, RFC1662), IPCP (RFC1332, RFC1877), PAP (RFC1334).
• SLIP (RFC1055).
• IPv4 (RFC791).
• ICMP (RFC792).
• UDP (RFC768).
• TCP (RFC793).
• DNS (RFC1034, RFC1035), client and server.
• TFTP (RFC1350), server.
• HTTP/0.9 (RFC2068 for HTTP/1.1), server.
• ping (RFC2151), client.
• finger (RFC1288), client.
• telnet (RFC854, RFC857, RFC858), client.

Unsupported features

Some of these limitations make this implementation non-compliant as per RFC1122 and RFC1123. You'll have to decide for yourself how significant the non-compliances are!

• The TCP layer isn't perfect.
• IP fragmentation (the MTU is over 1020 octets, though).
• All the IP option fields. They are ignored.
• Handling all the ICMP messages except for ECHO.
• TFTP RRQ (so files can't be fetched from CPC/IP).
• Recursive DNS queries (hey, they're not mandatory!). DNS on TCP (so zone transfers don't work).
• telnet commands, apart from the option commands, and telnet options, apart from echo and suppress-go-ahead.
• The resolver might give the wrong address for a hostname (this would occur if a nameserver gave an A RR for something like another nameserver before it gave the address for the given hostname)!

Oh, and CPC/IP doesn't support streaming RealVideo.

Portability

Although CPC/IP officially only supports Amstrad CPCs with Amstrad serial interfaces, it should work on compatible systems. The important points are that

• The serial chip must be Z80-DART-compatible, and be located at &fadc/fadd. The chip's interrupt line must be connected.
• The clock generator must be CTC-8253-compatible and be located at &fbdc/fbdd/fbdf. It must be clocked at 2 MHz.

Note the Pace serial interface satisfies these requirements, except that the interrupt line is not connected. It must therefore be polled. In turn, this means the datarate should be 4800 bps (though 9600 bps may be achievable if 8E2 or maybe just 8N2 framing is used -- it is in fact only necessary to use two stop bits on the remote side, so you might be able to get away with 8N1 on the CPC). You will need to make appropriate changes in config.z and rebuild.

The serial interface which appeared in CPC Amstrad International 1992-06/07 is also believed to be supported (untested); you'll need to make appropriate changes in config.z and rebuild to use this.

If you want to use the full 128K, then if your machine isn't a CPC6128 the important point is that

• The 128K must be selectable using OUT (&7fxx), &cx. 32K is used for rx/tx buffers and 16K is used for a loopback buffer; the rest may be used in the future to hide most of the code out of the main 64K.

Failing all this, though, it shouldn't be very difficult to port the system-dependent bits to a different system.

How to use

(The following assumes connection to a Linux box, and specifically to the version of Linux which happens to be on my box at home. I'm not a Linux guru, so it's unlikely I'll be able to help if the Linux bits don't work for you or make no sense! You can also connect straight to an ISP via a modem (ignoring all the bits about setting up the peer), as long as, if you're using SLIP, you use ifconfig to set your IP address everytime if your ISP gives out non-static IP addresses. Note: the Amstrad serial interface, at least, won't receive unless Carrier Detect is active, if hardware flow control is being used. The CPCAI serial interface won't ever receive if Carrier Detect is inactive, even if hardware flow control isn't being used! If you can't get your modem to force it active via a DIP switch, you'll have to type "AT&C0" blind to do so in software.)

• Somehow get CPC/IP into your CPC. Your options are:
  • Get the zipped sources, unzip them, transfer them onto a CPC disc, edit config.z to specify your CPC's IP address unless you're happy with the default 192.168.6.128, load main.z into Maxam and assemble it (set HIMEM to &27ff). The sources consist of config.z, main.z, telnet.z, finger.z, host.z, ping.z, ifconfig.z, httpd.z, tftpd.z, dnsd.z, resolv.z, tcp.z, udp.z, ip.z, icmp.z, slip.z, ppp.z, fcstab16.z, loopback.z, cs.z, stdio.z, serialdd.z, hosts.z, cons.z, printlib.z, utillib.z, linklist.z, and timeout.z.
  • Get the executable, change the third to sixth bytes to specify your CPC's IP address (or remember to set this at run-time as described below) unless you're happy with the default 192.168.6.128, transfer the file into your CPC, and load it to &3800 (set HIMEM to &27ff using "MEMORY &27ff").
  • Assemble it all using ZMAC and proceed as above with the executable.
• Remember, if you're trying to transfer a binary file to a CPC it must end up with an AMSDOS header. Put an AMSDOS header on using something like "head main.bin -l3800 -fcpcip.bin >cpcip.bin" (see cpcsutils for head). You can then transfer the file using "A$ = "cpcip.bin" : |SUCK, @a$" on the CPC and "blow cpcip.bin" (from the same package) on the source box, or tftp (remember to use binary mode!) if you've already managed to get just about any version of CPC/IP on your Amstrad CPC.
• Set up the serial port on the peer. You'll need to:
  • Set the serial port to use 8 data bits, no parity, and 1 stop bit. I think this is normally the default, which is a good thing because I don't know where or how to change it (though I suspect suitable stty lines somewhere in /etc/rc.boot/0setserial might do the trick)!
  • Edit /etc/inittab to allow connection via this serial port, at 9600 bps (or 2400 bps if using the CPC Amstrad International serial interface) and using hardware flow control, if appropriate. This is what I've got:
    T1:23:respawn:/sbin/getty -L -h ttyS1 9600
  • Use /sbin/init q to cause this file to be reparsed (only necessary the first time).
• Launch CPC/IP! "CALL &3800". You should see a login prompt. Log in using any account, to check the serial link is working OK. Log out.
• Set up SLIP or PPP on the peer. If you want to use PPP, you're probably best off contacting me for further details. If you want to have a go on your own, be aware that (a) the peer needs to support PAP, if it wants to authenticate, and you need to enter your PAP details in config.z, (b) there are no timeouts in the current implementation, so it could all just seize up, (c) there are no state checks in the current implementation, so it could all go haywire, (d) I would dare to suggest there's a bug in pppd version 2.3 patch level 5, which means you should turn off Van Jacobson compression (using "novj") (e) I've put in a workaround for buggy PPP implementations which unfortunately means that should the remote side send spurious control characters they won't be filtered out, (f) the local address and DNS server to use will automatically be requested (but can subsequently be overridden using ifconfig). For SLIP you'll need to:
  • Create a suitable account using adduser.
  • Make this account use /usr/sbin/sliplogin as its shell.
  • Suitably edit /etc/slip.hosts (use DYNAMIC as the remote address).
  • Suitably edit /etc/slip.tty (to specify your CPC's address).
  • Modify /etc/slip.login to make the MTU 1006 (CPC/IP would support 1023 but this is the Berkeley SLIP limit).
  • Make sure /usr/sbin/sliplogin is setuid (use "chmod u+s" if not) and the SLIP account has execute permission (fiddle with /etc/group if not).
  • Add your CPC to /etc/hosts using the address you allocated (optional).
  Alternatively, you could use slattach and ifconfig (as root), if you can work out the parameters (it's not particle physics). Here is a hint:
  slattach -L -p slip -s 9600 /dev/ttyS0 &
  ifconfig sl0 192.168.4.86 pointopoint 192.168.6.128 up mtu 1006
• Go back to your CPC. Log in using the SLIP account. You should now be able to use the stack:
  • You should be able to ping your CPC.
  • You should be able to transfer files to your CPC using TFTP on the remote machine. The filename should be AMSDOS-friendly, your disc should have enough free space, etc. Transferring files from your CPC using TFTP isn't possible yet, unfortunately.
  • You should be able to fetch files from your CPC using tipi, the HTTP/0.9 server. The URL to use is just what you'd expect; something like http://sugar/index.htm . Note if you're serving non-ASCII files, they should have AMSDOS headers; head from cpcsutils may be useful!
  • You should be able to make DNS queries regarding the bufo-house.org domain using rind, the Retro Internet Name Daemon. Type things like "host -a cpc [CPC]" and "host -a bufo-house.org [CPC]", where [CPC] is your CPC's IP address, on the remote machine. To use your own choice of DNS information, you can rebuild CPC/IP after changing dnsd.z, or you can load a DNS zone file into memory and place the base address at &380d.
  • To use any of the clients CPC/IP will have to realise/believe a SLIP connection has been established (shown by the presence of a command-line prompt ("> ")). One way to do so is to ping your CPC once. Another is to press Copy.
  • In all the clients you can use textual addresses defined in hosts.z. By default these are localhost (127.0.0.1), sugar (192.168.6.128) and koaks (192.168.4.86). To use your own choice of hosts, you can rebuild CPC/IP after changing hosts.z, or you can load a hosts.txt file into memory and place the base address at &3807.
  • If you want to change your CPC's address (only important for clients and if you didn't suitably set this in the source/executable if you don't want to use the default 192.168.6.128) you can use ifconfig. As for all the clients, you can get the syntax by entering the command name on its own. Note the clients may be more permissive regarding syntax than the syntax help would suggest; you should not rely on any short-cuts you find working in future versions of CPC/IP!
  • If you want to set the nameserver you can also use ifconfig. The default nameserver is 127.0.0.1 (localhost, your CPC), which doesn't serve much! The nameserver should preferably support recursive queries, because the resolver doesn't!
  • You should be able to finger other machines from your CPC. Remember by default there's no world-wide nameserver, so you'll have to type numeric addresses! You can use Ctrl-C to abort a connection.
  • You should be able to ping other machines from your CPC. This is one of the only three things you can ("usefully") do without a serial interface: specify a loopback address such as 127.0.0.1. Note the numeric parameters in this command should be less than 256. You can use Ctrl-C to abort pinging.
  • You can also make nameserver queries using host; this is the second thing you can do without a serial interface. For a hostname, you can either get all the numeric addresses corresponding to it, or all DNS information (using -a), or mail exchange information (using -m). You can also do reverse lookups on numeric addresses. You can use Ctrl-C to abort a lookup.
  • You should be able to telnet to other machines from your CPC. You can use Ctrl-[ to abort a connection. You can use this to fetch a page locally from tipi; this is the third and last thing you can do without a serial interface. If you're connected to the Internet, though, then you can use telnet to send and receive email and news, and even surf the net! Also, install this terminfo file using "tic cpc.tmi" (as root), select it using "export TERM=cpc" or your shell's equivalent, and you'll have a fully-functional console. The arrow keys work; Ctrl-Left/Right will do Home/End, Ctrl-Up/Down will do Page Up/Down, Clr will do Delete/Clear, Esc will do Esc, and Ctrl-Tab will do Insert.
  • There is a resolver which the clients automatically use if the address given isn't numeric and isn't in hosts.txt. This will automatically append the domain name specified in config.z -- "bufo-house.org" by default (rebuild to use yours!) -- to addresses without dots. If you need to make sure this doesn't happen for any reason, make the address absolute by putting a dot at the end. DNS is a bit of a monster, and so the resolver may well go wrong! If it does, please tell me, specifying the nameserver you were using and the query you were making (the address you were trying to resolve).
  • Press Ctrl-Esc to escape from CPC/IP. (If after acquiring a SLIP link you find you need to use CPC/IP as a terminal again (e.g. because your link fell over), press Copy.)

Well, wasn't that worth it?!

Other 8-bit TCP/IP stacks

• A BBC stack is available.
• A C64 stack is available as part of Lunix, the mini-Un*x for C64s.
• A Z88 stack, ZSock, is being developed.
• An MSX stack is being developed as part of UZIX, the mini-Un*x for MSX computers.
• An 8-bit Atari stack, ICE, is being developed.
• A stack aimed at the Gameboy is/was being developed.
• An Oric stack is being developed.
• A TI-99/4A stack is being developed.
• Another MSX stack was in development, but the effort appears to have stalled.
• If you know about other 8-bit stacks, please tell me!

Tangents

• cpcsutils is a set of programs to assist in |BLOWing and |SUCKing the Amstrad serial interface.
• I've written an Amstrad CPC screen saver. It coexists very nicely with CPC/IP: ignore what the readme says and instead LOAD"SCRSAVE.BIN", &7f00 and CALL &7f00 (the blank delay is at &7fde).
• I've put together an Amstrad CPC mode 2 text accelerator, based on code supplied by Richard WILSON. It too coexists very nicely with CPC/IP: ignore what the readme says and instead LOAD"SCRFAST.BIN", &7e00 and CALL &7e00.
• ZMAC is a Z80 assembler and ZDIS is a Z80 symbolic disassembler. If you're the sort of person who'd find these useful, you should be able to work out how to build and use them!
• I've written a document about various features of the Amstrad serial interface.
• I've written a document about various AMSDOS features.

What next?

If you like what you see, and would like things to go further, then please get in touch. If no-one cares, there's not much point (although it's quite an educational experience implementing the protocols).

As you will see if you look at the code, it's reasonably well structured (within the limitations of Maxam), and hooking in new stuff shouldn't be too difficult. The most interesting bit will be to work out how to allow things to hook in and then be called in the background. I've been thinking of schemes using OS events, but nothing's very firm yet. Currently the serial device driver is interrupt-driven, but the protocol stack is essentially polling-driven.

Can you contribute?

• If you're an Internet guru (or even if you're just keen!) and would like to contribute to CPC/IP, please get in touch.
• I don't know very much about the Internet protocols (just about all I know comes from reading the RFCs), and I could do with advice (for instance, which IP options and ICMP messages are, realistically, worth implementing?).
• Perhaps CPC/IP could become PCW/IP or S128/IP? The most important point to consider here is that CPC/IP uses both IX and IY. Please email me if you're even remotely interested in doing a port. All you need to get a basic pingable system is to:
  • Copy cs.z, icmp.z, ip.z, main.z, slip.z, printlib.z, utillib.z as is.
  • Copy config.z, changing values as appropriate (making sure you turn off all the bits you can).
  • Write serialdd.z.
  • Write stdio.z. You don't need the FILE_* or KL_* routines; the other routines need not be perfect.
• Perhaps device drivers could be written for other Amstrad serial interfaces (the only file which should need changing is serialdd.z).
• Perhaps you'd like to write a TFTP client, or an FTP client, or an IRC client, or a WWW browser, or a POP3 client, or an SMTP client, or an NNTP client, or an NFS client...

Copyright

Although I ultimately plan to make CPC/IP available Free, at this stage in its evolution I would like to keep it under reasonable control.

CPC/IP is Copyright (c) 1999-2001 Mark RISON. You may not distribute it without my permission (this includes modified/extended versions). Try emailing me for permission -- you should be pleasantly surprised!

Thank you for respecting this.

Mark RISON, <mrison@hotmail.com>, 2001-06-03

Thanks to Franck ARNAUD for hosting these pages.