Re: [lwip-users] DHCP + mem_malloc / pbuf allocation from ram (not the pool)

[Leon Woestenberg]

Hello Eric,

Eric Shufro wrote:

> When I start DHCP, I sends a discovery and then receives an offer, but it
> never sends a request since when it tries to allocate memory for the dhcp
> request, an error is returned: not enough memory.
>
> The error's origin is in dhcp.h, function dhcp_create_request() when it
> calls:
>
> dhcp->p_out = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dhcp_msg), PBUF_RAM);
>
>  

So sizeof(struct dhcp_msg) is eating the few bytes of left-over RAM? You 
could try to
lay the structure in ROM, but that will only work if you do not fill in 
the "caddr" member
(i.e. leave it zero), so you cannot (re-)request an old lease then.

Also, the MAC address should be correct for each ROM dhcp_msg.

Also, see if you can reduce the dhcp_msg struct size in dhcp.h. It has 
space for so-called
DHCP options and I might have gone a bit on the safe size to allow users 
to add
additional options (like recently, the DNS server option was added).

Hope any of these hints can help you out. Let us know if it did please!

Regards,

Leon.