pack the fields in dhcp_msg.This way DHCP works on non-byte aligned archs too.

src/include/lwip/dhcp.h

@@ -51,32 +51,32 @@ PACK_STRUCT_BEGIN
 // minimum set of fields of any DHCP message
 struct dhcp_msg
 {
-  u8_t op;
-  u8_t htype;
-  u8_t hlen;
-  u8_t hops;
-  u32_t xid;
-  u16_t secs;
-  u16_t flags;
-  u32_t ciaddr;
-  u32_t yiaddr;
-  u32_t siaddr;
-  u32_t giaddr;
+  PACK_STRUCT_FIELD(u8_t op);
+  PACK_STRUCT_FIELD(u8_t htype);
+  PACK_STRUCT_FIELD(u8_t hlen);
+  PACK_STRUCT_FIELD(u8_t hops);
+  PACK_STRUCT_FIELD(u32_t xid);
+  PACK_STRUCT_FIELD(u16_t secs);
+  PACK_STRUCT_FIELD(u16_t flags);
+  PACK_STRUCT_FIELD(u32_t ciaddr);
+  PACK_STRUCT_FIELD(u32_t yiaddr);
+  PACK_STRUCT_FIELD(u32_t siaddr);
+  PACK_STRUCT_FIELD(u32_t giaddr);
 #define DHCP_CHADDR_LEN 16U
-  u8_t chaddr[DHCP_CHADDR_LEN];
+  PACK_STRUCT_FIELD(u8_t chaddr[DHCP_CHADDR_LEN]);
 #define DHCP_SNAME_LEN 64U
-  u8_t sname[DHCP_SNAME_LEN];
+  PACK_STRUCT_FIELD(u8_t sname[DHCP_SNAME_LEN]);
 #define DHCP_FILE_LEN 128U
-  u8_t file[DHCP_FILE_LEN];
-  u32_t cookie;
+  PACK_STRUCT_FIELD(u8_t file[DHCP_FILE_LEN]);
+  PACK_STRUCT_FIELD(u32_t cookie);
 #define DHCP_MIN_OPTIONS_LEN 68U
 // allow this to be configured in lwipopts.h, but not too small
 #if ((!defined(DHCP_OPTIONS_LEN)) || (DHCP_OPTIONS_LEN < DHCP_MIN_OPTIONS_LEN))
 // set this to be sufficient for your options in outgoing DHCP msgs
 #  define DHCP_OPTIONS_LEN DHCP_MIN_OPTIONS_LEN
 #endif
-	u8_t options[DHCP_OPTIONS_LEN];
-};
+  PACK_STRUCT_FIELD(u8_t options[DHCP_OPTIONS_LEN]);
+} PACK_STRUCT_STRUCT;
 PACK_STRUCT_END
 #ifdef PACK_STRUCT_USE_INCLUDES
 #  include "arch/epstruct.h"
@@ -97,13 +97,11 @@ void dhcp_inform(struct netif *netif);
 #if	DHCP_DOES_ARP_CHECK
 void dhcp_arp_reply(struct ip_addr *addr);
 #endif
-// to be called regularly
-#if (DHCP_TIMER_CALLBACKS == 0)
+
 // to be called every minute
 void dhcp_coarse_tmr(void);
 // to be called every half second
 void dhcp_fine_tmr(void);
-#endif
  
 // DHCP message item offsets and length 
 #define DHCP_MSG_OFS (UDP_DATA_OFS)