| lwIP
    2.0.3
    Lightweight IP stack | 
| Data Fields | |
| mem_size_t | next | 
| mem_size_t | prev | 
| u8_t | used | 
The heap is made up as a list of structs of this type. This does not have to be aligned since for getting its size, we only use the macro SIZEOF_STRUCT_MEM, which automatically aligns.
| mem_size_t mem::next | 
index (-> ram[next]) of the next struct
| mem_size_t mem::prev | 
index (-> ram[prev]) of the previous struct
| u8_t mem::used | 
1: this area is used; 0: this area is unused