I started from an example of NXP SDK for LPC546xx MCUs. I'm using
baremetal (NO_SYS=1) and I found the following warning in
enet_ethernetif_lpc.c, function ethernetif_tx_release():
---
#if NO_SYS
#if defined(LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT) &&
LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
pbuf_free(p);
#else
#error "Bare metal requires LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT=1
because pbuf_free() is being called from an ISR"
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
...
---
It seems NXP code calls pbuf_free() inside ISR and this behaviour must
be known to lwip by setting 1 to this macro. However it seems this macro
is checked only in mem.c, if MEM_USE_POOLS is defined.
In my application I don't define MEM_USE_POOLS, so it is set to 0 by
default in opt.h.
Does it mean I can avoid setting LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEX?
I would like to set it to 0, because of the following warning found in
opt.h:
---
* ATTENTION: As you can see from the above description, this leads to
dis-/
* enabling interrupts often, which can be slow! Also, on low memory,
mem_malloc
* can need longer.
---
However NXP code uses #error if this macro is not set, so I suspect
there's a real risk to avoid setting it.
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