Re: [lwip-users] MEM_SIZE

[Giuseppe Modugno]

Il 14/03/2018 16:42, Giuseppe Modugno ha scritto:
> I was experimenting with lwip memory allocator. I defined:
>
> #define MEM_LIBC_MALLOC  0
> #define MEM_USE_POOLS      0
> #define MEM_SIZE  (32 * 1024)
> #define LWIP_RAM_HEAP_POINTER  ( (void *)0x2007C000 )
>
> I'm using LPC1768 that has a 32kB SRAM block starting from address 
> 0x2007C000. However I have a Hard Fault error during mem_init(), 
> because ram_end is initialized to 0x2007C000 + (32*1024), that is over 
> the available memory.
>
> So MEM_SIZE should be smaller than available heap memory.

Another question regarding memory management of lwip.

I understood lwip uses memory pools for many things (TCP pcbs, UDP pcbs, 
RAW pcb, timers and so on). The memory pools are defined in 
include/lwip/priv/memp_std.h.
They aren't allocated from the heap, but from pools. I think because it 
is supposed they must be allocated frequently, so they could bring to 
fragmentation and the allocation should be fast.

Does lwip use strictly heap (mem_malloc) for its own purposes? It seems 
yes (I see some mem_malloc calls in httpd, dhcp, pbuf, ...).
Is it possible to compile lwip so it doesn't use heap at all?

I think with the following options:

#define MEM_LIBC_MALLOC  0
#define MEM_USE_POOLS      1
#define MEM_USE_CUSTOM_POOLS 1  /* Needed by MEM_USE_POOLS */

In this way, heap implementation isn't a real heap, but a set of 
different-sized pools. This set is defined in arhc/lwippools.h. Is it 
correct?

I tried to compile with this options, but I have this error (for example 
compiling memp.c):

mingw32-gcc.exe -Wall -std=c11 -Wall -pedantic -Wparentheses 
-Wsequence-point -Wextra -Wundef -Wshadow -Wpointer-arith -Wcast-qual 
-Wwrite-strings -Wold-style-definition -Wcast-align -Wmissing-prototypes 
-Wredundant-decls -Wnested-externs -Wno-address -Wunreachable-code 
-Wuninitialized -Wlogical-op -Wno-format -g -DLWIP_DEBUG -DDEBUG 
-Isrc\lwip\src\include -Isrc -Isrc\ports\mingw\lwip_arch 
-Isrc\ports\mingw -Isrc\bus -Isrc\WpdPack\Include -I..\..\..\work_git 
-Isrc\lwip\src\include\lwip\apps -c 
C:\Users\Giuseppe\Documents\work_git\webserver\webserver\src\lwip\src\core\memp.c 
-o mingw\Debug\src\lwip\src\core\memp.o
In file included from src\lwip\src\include/lwip/memp.h:58:0,
                 from 
C:\Users\Giuseppe\Documents\work_git\webserver\webserver\src\lwip\src\core\memp.c:48:
src\lwip\src\include/lwip/priv/memp_priv.h:89:5: error: expected 
expression before ')' token
     ) ,
     ^