RE: [cc65] cc65 + tcp/ip howto and/or example

Oliver, I wasn't disrespecting uIP. uIP is obviously a great success,
although the argument from popularity is somewhat moot, as uIP is about
the only one out there. By 'convoluted' I meant that the coding style is
not as clean ( in my opinion ) as it could be, and there are a lot of
generalizations that I don't need as I am targeting a specific machine.
I am using a lot of machine specific things and have no desire to be
generalized in the way uIP is. 

I am familiar with event driven programming, and you certainly are
correct that this is the basic architecture that must be used. But uIP
is not the perfect solution for all small TCP needs.

Contiki is a fine system, but has a huge amount of overhead if all you
want to do is write a TCP driver. By the time Contiki finishes loading
on an Atari, there is very little application space left.

My goal is to write a small, machine-specific driver for supporting
TCP-IP on the Atari. If it's been done already, well then so be it,
after I'm done we'll have another, and extra options never hurt.

Dan Winslow
Director of Information Technology, AIM INSTITUTE
1905 Harney Street, Suite 700
Omaha, NE 68102
402-345-5025 x156
dwinslow@aiminstitute.org
www.aiminstitute.org

-----Original Message-----
From: owner-cc65@musoftware.de [mailto:owner-cc65@musoftware.de] On
Behalf Of Oliver Schmidt
Sent: Monday, January 03, 2011 7:23 AM
To: cc65@musoftware.de
Subject: Re: [cc65] cc65 + tcp/ip howto and/or example

Hi Dan,

> I am doing a stack for the Atari at the moment. I looked at uIP and
IP65
> both. I found uIP too convoluted to use directly. IP65 seemed a lot
cleaner
> but I didn't want to have to do it all in ML, as I'm lazy. So I took
uIP
> apart and used bits of it to start what I have now. As a starting
point, uIP
> was very helpful.

Just some thoughts...

If uIP would be too convoluted would it be then the by far most
popular TCP/IP stack for really small machines? Maybe it is in fact
rather well designed. Probably because the creator implemented already
several other TCP/IP stacks before and put all his experience into
uIP. Possibly this is the reason why i.e. CISCO choose uIP as basis
for their IPv6-for-small-devices investments.

Every non-trivial network application needs to react on theese three
things:
1. network traffic
2. user interaction
3. timeout
The only way to do this in a both flexible and efficient manner is
event driven programming. So from this perspective alone it is already
evident that the event based uIP API is the right choice as it allows
for easy integration into any event driven program.

Additionally the event based uIP API allows for a non-buffering
copy-free handling of things like retransmissions. So it is the right
choice even for minimal programs not requiring an event driven
archtecture otherwise.

So I can't follow at all any argumentation saying uIP is "to much".
Rather it is in many/most cases still "to little". And therefore the
uIP creators don't supply uIP standalone anymore but only as part of
Contiki.

The Contiki core is about dispatching events. The event senders and
receivers are called processes. A typical Contiki program hosts
several processes:
1. One process polling the network card for new frames and placing
them in "the" buffer.
2. One process polling the keyboard (and mouse) and broadcasting user
events on user interaction.
3. One process polling the current timme and broadcasting timer events
on timeouts.
4. One process hosting uIP polling "the" buffer and sending events to
the uIP user process.
5. One (or several) process(es) hosting the actual application code
working in a pure event driven way (no polling at all).

So the several "internal" processes basically act as converters
abstracting from different low level inputs to a common uniform event
system.

Interestingly this basic/classic/pure Contiki core is better suited to
cc65 targets then to the targets it is supposed to run on today
(embedded devices, especially wireless sensors). Those devices make
heavy usage of interrupts trying to put the main processor to sleep as
much as possible to save engery. Getting Contiki to work in these
environments requires some additional tricks.

The cc65 C library on the other hand doesn't offer interrupt based
APIs (apart from the mouse cursor handlers) so the classic Contiki is
a perfect fit by calling keypressed() for user interaction polling and
clock() for timeout polling. And regarding the network it happens to
be just the same. The CS8900A chip doesn't support interrupts in 8-bit
I/O mode so Contiki is a perfect fit by polling the chip.

So from my perspective there's no artificial / unnecessary overhead in
any area at all. Rather the cc65 C library, uIP, Contiki and the
CS8900A chip work together perfectly smooth as they all follow the
same paradigm :-)

There's only one minor exception - which I already mentioned in
another thread before: uIP/Contiki put great effort in avoiding to use
the C heap but the cc65 module loader is hardwired to load modules on
the C heap. Allowing to provide the cc65 module loader with an
allocator callback function (in the same way there is a read callback
function) would allow avoid that unncessary linking-in of the C heap
code.

Certainly one can pull together some networking code and have some
packets sent/received but when I see i.e. a blocking function for
getting an IP address via DHCP which then internally calls the C64
kernal keyboard handler now and then in order to allow the user to
interrupt the waiting for a DHCP reply then this at best a hack to me
but certainly no framework to build something real upon.

The Breadbox64 twitter client on the other hand is a perfect example
that Contiki allows to write portable, really usefully, reliable,
interactive and responsive network apps without being a Contiki
insider - and moving Breadbox64 to IPv6 will be a piece of cake :-)

Just my two (quite lenghty) cents,
Oliver

P.S.: I ported Contiki to the Atari in a few days (after understanding
enough of the Atari). It's in the CVS and works out-of-the-box with
the Atari Ethernet solution. So I personally see more need in the
getting that Ethernet solution out to the people than in creating yet
another TCP/IP stack ;-))
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