[Libwebsockets] LWS on the Texas Instruments SimpleLink CC3220.

Ralph Corderoy ralph at inputplus.co.uk
Sun May 17 15:54:29 CEST 2020


Hi Andy,

Thanks for the prompt reply.

> > (TI say this is to make it more awkward to accidentally have a
> > plain-text connection.) 
>
> Hm.

Quite.  I suspect it's more to do with fitting TLS in given the narrow
interconnect between the two CPUs.

> > It follows from the above that FreeRTOS is providing threading, a
> > heap, ..., but not a TCP/IP stack.
>
> Normally freertos is paired with lwip.  If there's no lwip on your cpu
> there's no posix sockets, no socket fd and no easy way for lws to talk
> to it IIUI.

TI provide a range of SlNet* APIs which look like BSD sockets if
squinting, and ‘SlNetSock provides a standard BSD API, built atop the
SlNet* APIs’ says
http://dev.ti.com/tirex/explore/content/simplelink_cc32xx_sdk_4_10_00_07/docs/ns/html/SlNetSock_overview.html

Of course, the seamlessness of the BSD API support may be found wanting
when stressed by LWS.  For example, AFAICS its select(2) works for
reading, accepts, and connects, but not writes so there's no detecting
when the output buffer has space.

> Tbh it sounds like the kind of proprietary mess it's best to stay as
> far as possible from.

Yes.  Did I mention its HTTP client only allows access to a restricted
set of headers from the server's reply, blocking implementation of an
upgrade to WebSocket?  :-)

Next time, I'd be interested in a plain Cortex-M4 with FreeRTOS and
lwip, or Zephyr, aided by something like the Microchip ATECC608A.

> From lws side, if there's posix sockets api it can likely interface to
> it without huge pain, since the tls is handled transparently.  If
> there's not, the key point is how can you do the equivalent of a poll
> wait?  It seems yoll basically need to add a plat implementation if
> it's like that.
>
> LWS_PLAT_FREERTOS is already supporting lwip + freertos, if it's
> basically that wired up to an opaque but transparent-in-operation tls
> proxy basically then it should work out.

Yes, this sounds closest to what appears to be there.  I'll take a look.

Thanks for the guidance.

-- 
Cheers, Ralph.


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