I'm using LWIP for TCP/IP communication on a TI Tiva microcontroller (a
TM4C1294NCPDT). TI includes LWIP 1.4.1 in its TivaWare package. I've read
that LWIP is not threadsafe, however, I'm not sure exactly what that means
in my context where I'm using it with no operating system on the single
core TI Tiva microcontroller.
It seems the way LWIP works on the Tiva is during the SysTick interrupt,
you call the lwIPTimer function giving it an amount of time for
processing. lwIPTimer then triggers the Tiva's ethernet interrupt and it
does it's processing for the given amount of time.
Inside the lwIPTimer function, I see this comment above the line of code
that triggers the Tiva's ethernet interrupt:
//
// Generate an Ethernet interrupt. This will perform the actual work
// of checking the lwIP timers and taking the appropriate actions.
This is
// needed since lwIP is not re-entrant, and this allows all lwIP calls
to
// be placed inside the Ethernet interrupt handler ensuring that all
calls
// into lwIP are coming from the same context, preventing any reentrancy
// issues. Putting all the lwIP calls in the Ethernet interrupt handler
// avoids the use of mutexes to avoid re-entering lwIP.
//
My current code is making calls to tcp_write() and tcp_output() *outside*
of the ethernet interrupt handler. My calls to tcp_write() and
tcp_output() occur in the SysTick interrupt just before I call
lwIPTimer(). Does this violate the advice in the comment above? I'm
unsure since these are "tcp_" calls and not "lwIP" calls.
Can anyone please clarify? Thank you.
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