Hi Tom,

The Circuit Cellar version doesn't implement TCP. It implements UDP/IP
over PPP. In fact, it doesn't even implement a fully RFC-compliant
version of that.

Nonetheless, it's an impressive feat. This is why I *strongly* suspect
that the device mentioned on slashdot doesn't do what the author claims.

TCP is a *lot* (ie. order of magnitude) more complex than UDP, and,
among other things, requires a copy of un-ACK'd data to be kept for
resending (in the event of a lower-level IP packet going astray). Since
the PIC sure as hell doesn't have space for this, is he storing this
data on the EEPROM? Not a good idea if you have a limited write-cycle
lifespan.

I'm particularly impressed by his codesize breakdown - apparently
HTTP/1.0 and I2C can be implemented in 3~99 instructions. Does this mean
between 3 and 99 instructions? I'd like to meet the guy who can
implement HTTP and I2C in 3 instructions. UDP+TCP in 70~99? If it's 99
instructions, it ain't TCP (at least not in any meaningful sense).

Cheers,
Ben



Tom Handley wrote:
>
>    Adam, I have'nt looked at the site but the current Circuit Cellar magazine
> (#108) has an article about a stripped-down TCP/IP stack implemented in a
> PIC12C672 for remote sensing on the internet.
>
>    - Tom
>
> At 04:54 PM 7/14/99 -0400, Adam Davis wrote:
> >Well...  I'm a bit skeptical.  Mind you, I've not implemented a tcp/ip stack
> >anywahere, nevemind on a pic, but he has code that:
> >
> >Handles 115200 serial reception and transmission
> >Handles and serves data from an eeprom
> >With a fully tcp/ip stack and http 1.0 server between the two
> >On a chip running at 4MHz.
> >
> >To my knowledge, none of the 12cxxx chips have usart, so he must be bit
> >banging.  Probably no error correction.  He could be doing a funny
> interrupt on
> >change and timer combination for reception...
> >
> >I suppose it is possible, but I only say that because I don't know as much as
> >I'd like to know about the tcp/ip stack, which is the kicker, here...
> >
> >-Adam
> >
> >Matt Bennett wrote:
> >>
> >> I don't think anyone has mentioned this in the past few seconds...
> >>
> >> This was just posted on slashdot:
> >>
> >> http://slashdot.org/articles/99/07/14/1937221.shtml
> >>
> >> "Jason Asbahr writes " From the wearables list, Shrikumar wrote:
> >>          I'd like to announce what is a really tiny implementation of
> >>          TCP/IP stack and a really really tiny web-server. "
> >>
> >> Which contains a pointer to:
> >>
> >> http://www-ccs.cs.umass.edu/~shri/iPic.html
> >>
> >> Matt Bennett