Re: [lwip-users] Little endian

[Adriano Pallavicino]

Hi Fabi, have you followed this guide http://lwip.wikia.com/wiki/Porting_for_an_OS ? In particular:
"Packet headers data is stored in network byte order which is the the big-endian mode. If your processor architure is little-endian, then we need to convert data using htons()/htonl()/ntohs()/ntohl() functions."

Here an example (the following code use CMSIS, so you must be sure to have it enabled)


---------------------------
u16_t
lwip_le_htons(u16_t n)
{
    return ((n & 0xff) << 8) | ((n & 0xff00) >> 8);
}
 
/**
 * Convert an u16_t from network- to host byte order.
 *
 * @param n u16_t in network byte order
 * @return n in host byte order
 */
u16_t
lwip_le_ntohs(u16_t n)
{
    return ((n & 0xff) << 8) | ((n & 0xff00) >> 8);
}
 
/**
 * Convert an u32_t from host- to network byte order.
 *
 * @param n u32_t in host byte order
 * @return n in network byte order
 */
u32_t
lwip_le_htonl(u32_t n)
{
    return __REV(n);
}
 
/**
 * Convert an u32_t from network- to host byte order.
 *
 * @param n u32_t in network byte order
 * @return n in host byte order
 */
u32_t
lwip_le_ntohl(u32_t n)
{
    return __REV(n);
}
-------------------------------------------

you must insert these functions in /core/def.c and check the #define chain

Bye Adriano

2014-06-26 11:14 GMT+02:00 Fabian Cenedese <address@hidden>:

Hi

I'm using lwip 1.4.1 on big endian targets and it works. Now I
want to use the same software on little endian targets (ARM)
and have problems. Should that work from the lwip part? The
Ethernet frame of course is always big endian why it works
without problems on big endian targets. However I'm not sure
that all places do the correct conversion between host and
network order.

E.g. the IP address for the interface:

IP4_ADDR(ipaddr, 192, 168, 1, 197)
netif_add(&m_Netif, &ipaddr...

gives a debug trace

... set to 197.1.168.192

Is the trace wrong or did I give a wrong address?


Sending (e.g. ARP reply):
ip_output_if_opt

The ip address is copied directly into the frame:
    ip_addr_copy(iphdr->src, *src);

Shouldn't that be
    ip_addr_set_hton(&iphdr->src, src);

if the runnig hardware is little endian?

And yes, I do have
#define BYTE_ORDER LITTLE_ENDIAN

Thanks

bye  Fabi


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--
Adriano Pallavicino