diff --git a/cpu/z80/Makefile.z80 b/cpu/z80/Makefile.z80
index b223c2c2a..1255a9ef6 100644
--- a/cpu/z80/Makefile.z80
+++ b/cpu/z80/Makefile.z80
@@ -2,7 +2,7 @@
 # Makefile for z80/SDCC
 # @author Takahide Matsutsuka <markn@markn.org>
 #
-# $Id: Makefile.z80,v 1.1 2007/08/30 14:39:16 matsutsuka Exp $
+# $Id: Makefile.z80,v 1.2 2007/09/01 11:14:52 matsutsuka Exp $
 #
 
 ### Compiler definitions
@@ -19,11 +19,11 @@ CFLAGS  += -I. -I$(CONTIKI) -I$(CONTIKI)/core -I$(CONTIKI_CPU) \
            ${addprefix -I,$(APPDIRS)} $(APP_INCLUDES) \
            --std-c99 --vc -mz80
 
-ASFLAGS += 
+ASFLAGS += -l
 LDFLAGS += -mz80
 AROPTS = -a
 
-CONTIKI_SOURCEFILES += strcasecmp.c mtarch.c
+CONTIKI_SOURCEFILES += strcasecmp.c mtarch.c uip_arch.c
 CONTIKI_ASMFILES += uip_arch-asm.S
 
 contiki-$(TARGET).o: $(CONTIKI_OBJECTFILES) $(PROJECT_OBJECTFILES) $(CONTIKI_ASMOBJECTFILES)
@@ -32,4 +32,8 @@ contiki-$(TARGET).o: $(CONTIKI_OBJECTFILES) $(PROJECT_OBJECTFILES) $(CONTIKI_ASM
 contiki.ihex: contiki-$(TARGET).o
 	$(LD) $(LDFLAGS) -DAUTOSTART_ENABLE $(CONTIKI_TARGET_MAIN) -lcontiki-$(TARGET).o -o $@
 
+CUSTOM_RULE_S_TO_OBJECTDIR_O = 1
+$(OBJECTDIR)/%.o: %.S
+	$(AS) $(ASFLAGS) -o $@ $<
+
 #CONTIKI_TARGET_DIRS += $(CONTIKI_CPU)/net
diff --git a/cpu/z80/contiki-sdcc-conf.h b/cpu/z80/contiki-sdcc-conf.h
index 28637df4f..6678aa86e 100644
--- a/cpu/z80/contiki-sdcc-conf.h
+++ b/cpu/z80/contiki-sdcc-conf.h
@@ -27,16 +27,16 @@
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- * $Id: contiki-sdcc-conf.h,v 1.1 2007/08/30 14:39:16 matsutsuka Exp $
+ * $Id: contiki-sdcc-conf.h,v 1.2 2007/09/01 11:14:52 matsutsuka Exp $
  *
  */
 
 /*
  * \file
- *		This file contains a set of configuration for using SDCC as a compiler. 
+ *	This file contains a set of configuration for using SDCC as a compiler. 
  * 
  * \author
- *		Takahide Matsutsuka <markn@markn.org>
+ *	Takahide Matsutsuka <markn@markn.org>
  */
  
 #ifndef __CONTIKI_SDCC_CONF_H__
@@ -64,15 +64,22 @@ typedef unsigned int size_t;
 #define CCIF
 #define CLIF
 
-/* uIP configurations */
-/* uip_add32 */
+/*
+ * Enable architecture-depend checksum calculation
+ * for uIP configuration.
+ * @see uip_arch.h
+ * @see uip_arch-asm.S
+ */
 #define UIP_ARCH_ADD32		1
+#define UIP_ARCH_CHKSUM	1
+#define UIP_ARCH_IPCHKSUM
 
-#define uip_ipaddr_copy(dest, src)		\
-	memcpy(dest, src, sizeof(*dest))
 #define CC_CONF_ASSIGN_AGGREGATE(dest, src)	\
 	memcpy(dest, src, sizeof(*dest))
 #define CC_CONF_INC_CAST_POINTER(type, data)	\
-    data = ((type) data) + 1
+    data = ((type)data) + 1
+
+#define uip_ipaddr_copy(dest, src)		\
+	memcpy(dest, src, sizeof(*dest))
 
 #endif /* __CONTIKI_SDCC_CONF_H__ */
diff --git a/cpu/z80/uip_arch-asm.S b/cpu/z80/uip_arch-asm.S
index b31fbf7cd..0f9decbc1 100644
--- a/cpu/z80/uip_arch-asm.S
+++ b/cpu/z80/uip_arch-asm.S
@@ -9,14 +9,21 @@
 ;;; \author
 ;;; 	Takahide Matsutsuka <markn@markn.org>
 ;;; 
-	
+	.module	uip_arch-asm
+
+	;; export symbols
 	.globl _uip_add32
-	.globl _uip_acc32
+	.globl _uip_arch_chksum
+	.globl _uip_chksum
 	
-	.area _GSINIT
+	;; import symbols
+	.globl _uip_acc32
+	.globl _uip_buf
 
-	.area _DATA	
+	.area	_DATA	
 
+	.area	_GSINIT
+	
 	.area	_CODE
 
 	;; ---------------------------------
@@ -28,58 +35,187 @@
 	;; ---------------------------------
 _uip_add32_start::
 _uip_add32:
-	ld	hl,#2
-	add	hl,sp
-	;; HL indicates #_op32l
-	ld	e,(hl)
+	;; HL = #_op32l
+	ld	hl, #2
+	add	hl, sp
+
+	;; DE = #(_op32)
+	ld	e, (hl)
 	inc	hl
-	ld	d,(hl)
+	ld	d, (hl)
 	inc	hl
-	ld	c,(hl)
+
+	;; BC = op16
+	ld	c, (hl)
 	inc	hl
-	ld	b,(hl)
-	;; BC indicates op16
-	ld	l,e
-	ld	h,d
-	;; HL indicates #_op32
-	ld	de,#_uip_acc32
-	;; DE indicates #_uip_acc32
-	;; uip_acc32[0] = op32[0] + op16l;
-	ld	a,(hl)
-	add	a,c
-	ld	(de),a
-	inc	hl
-	inc	de
-	;; uip_acc32[1] = op32[1] + op16h + carry;
-	ld	a,(hl)
-	adc	a,b
-	ld	(de),a
-	inc	hl
-	inc	de
-	jr	nc,_uip_add32_exit
-	ld	a,(hl)
+	ld	b, (hl)
+
+	;; HL = #(_op32) + 3
+	ld	hl, #3	
+	add	hl, de
+	
+	;; DE = #_uip_acc32 + 3
+	ld	de, #_uip_acc32 + 3
+
+	;; uip_acc32[3] = op32[3] + op16l;
+	ld	a, (hl)
+	add	a, c
+	ld	(de), a
+	
+	;; uip_acc32[2] = op32[2] + op16h + carry;
+	dec	hl
+	dec	de
+	ld	a, (hl)
+	adc	a, b
+	ld	(de), a
+	jr	nc, _uip_add32_nocarry1
+
+	;; uip_acc32[1]
+	dec	hl
+	dec	de
+	ld	a, (hl)
 	inc	a
-	ld	(de),a
-	inc	hl
-	inc	de
-	jr	nc,_uip_add32_exit
-	ld	a,(hl)
+	ld	(de), a
+	jr	nz, _uip_add32_nocarry0
+
+	;; uip_acc32[0]
+	dec	hl
+	dec	de
+	ld	a, (hl)
 	inc	a
-	ld	(de),a
+	ld	(de), a
 	ret
-_uip_add32_exit:	
-	ld	a,(hl)
-	ld	(de),a
-	inc	hl
-	inc	de
-	ld	a,(hl)
-	ld	(de),a
+_uip_add32_nocarry1:
+	;; uip_acc32[1]
+	dec	hl
+	dec	de
+	ld	a, (hl)
+	ld	(de), a
+
+_uip_add32_nocarry0:
+	;; uip_acc32[0]
+	dec	hl
+	dec	de
+	ld	a, (hl)
+	ld	(de), a
 	ret			
 _uip_add32_end::		
+	
 	;; ---------------------------------
-	;; u16_t uip_chksum(void);
+	;; static u16_t chksum(u16_t sum, const u8_t *data, u16_t len)
 	;; Stack; retl reth suml sumh datal datah lenl lenh
 	;; ABCDEHL____
 	;; return HL
-	;; _uip_acc32 = op32 + op16
 	;; ---------------------------------
+_uip_arch_chksum_start::	
+_uip_arch_chksum:
+	push	ix
+	;; IX = #_suml
+	ld	ix, #4
+	add	ix, sp
+	;; BC = sum
+	ld	c, 0(ix)
+	ld	b, 1(ix)
+	;; DE = #data
+	ld	e, 2(ix)
+	ld	d, 3(ix)
+	
+	;; (lenl, lenh) <- dataptr + len - 1 (last address)
+	;; (len) + DE - 1 -> (len)
+	ld	l, 4(ix)
+	ld	h, 5(ix)
+	add	hl, de
+	dec	hl
+	ld	4(ix), l
+	ld	5(ix), h
+
+_uip_arch_chksum_loop:
+	;; compare HL(last address) and DE(dataptr)
+	;; HL - DE
+	;; if (HL < DE) C,NZ else if (HL = DE) NC,Z=1 otherwise NC,NZ
+	;;  HL = last address, DE = current pointer
+	ld	l, 4(ix)
+	ld	h, 5(ix)
+	
+	ld      a, h
+	sub     d
+	jr	nz, _uip_arch_chksum_compared
+	ld      a, l
+	sub     e
+	;; if (last address == dataptr) _uip_arch_chksum_loop_exit_add_trailing
+	jr	z, _uip_arch_chksum_loop_exit_add_trailing
+_uip_arch_chksum_compared:
+	;; if (last address > dataptr) _uip_arch_chksum_loop_exit
+	jr	c, _uip_arch_chksum_loop_exit
+	;; bc = dataptr[0],dataptr[1] + bc
+	ld	a, (de)
+	ld	h, a
+	inc	de
+	ld	a, (de)
+	ld	l, a
+	push	hl
+	add	hl, bc
+	inc	de
+	ld	b, h
+	ld	c, l
+	;; HL = t
+	pop	hl
+	;; BC - HL
+	;; if (sumBC < tHL) sum++
+	ld	a, b
+	sub	h
+	jr	nz, _uip_arch_chksum_compared_t
+	ld	a, c
+	sub	l
+_uip_arch_chksum_compared_t:
+	jr	nc, _uip_arch_chksum_nocarry_t
+	inc	bc
+_uip_arch_chksum_nocarry_t:
+	jr	_uip_arch_chksum_loop
+_uip_arch_chksum_loop_exit_add_trailing:
+	;; HL = last address
+	;; bc = bc + (last address)<<8
+	ld	a, b
+	add	a, (hl)
+	ld	b, a
+	jr	nc, _uip_arch_chksum_loop_exit
+	inc	bc
+_uip_arch_chksum_loop_exit:
+	ld	l, c
+	ld	h, b
+	pop	ix
+	ret
+_uip_arch_chksum_end::	
+	
+	;; ---------------------------------
+	;; u16_t uip_chksum(void);
+	;; Stack; retl reth datal datah lenl lenh
+	;; ABCDEHL____
+	;; return HL
+	;; return htons(chksum(0, (u8_t *)data, len));
+	;; ---------------------------------
+_uip_chksum_start::
+_uip_chksum:
+	ld	hl, #5
+	add	hl, sp
+	;; HL indicates #_lenh
+	ld	b, #2
+_uip_chksum_loop:
+	ld	d, (hl)
+	dec	hl
+	ld	e, (hl)
+	dec	hl
+	push	de
+	djnz	_uip_chksum_loop
+	ld	bc, #0
+	push	bc
+	call	_uip_arch_chksum
+	pop	af
+	pop	af
+	pop	af
+	;; convert to BIG ENDIAN (htons)
+	ld	a, l
+	ld	l, h
+	ld	h, a
+	ret
+_uip_chksum_end::
diff --git a/cpu/z80/uip_arch.c b/cpu/z80/uip_arch.c
new file mode 100644
index 000000000..63d40ce56
--- /dev/null
+++ b/cpu/z80/uip_arch.c
@@ -0,0 +1,216 @@
+/*
+ * Copyright (c) 2007, Takahide Matsutsuka.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above
+ *    copyright notice, this list of conditions and the following
+ *    disclaimer in the documentation and/or other materials provided
+ *    with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
+ * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+ * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $Id: uip_arch.c,v 1.1 2007/09/01 11:14:52 matsutsuka Exp $
+ *
+ */
+ /*
+  * \file
+  * 	Z80 architecture-depend uip module
+  * 	for calculating checksums
+  * \author
+  * 	Takahide Matsutsuka <markn@markn.org>
+  */
+
+#include <stddef.h>
+#include "uip_arch.h"
+
+const u16_t SIZEOF_UIP_IPADDR_T = sizeof(uip_ipaddr_t);
+const u16_t OFFSET_TCPIP_HDR_LEN = offsetof(struct uip_tcpip_hdr, len);
+const u16_t OFFSET_TCPIP_HDR_SRCIPADDR = offsetof(struct uip_tcpip_hdr, srcipaddr);
+
+/*--------------------------------------------------------------------------*/
+static void upper_layer_chksum() {
+__asm
+	;; ---------------------------------
+	;; static u16_t upper_layer_chksum(u8_t proto);
+	;; Stack; retl reth
+	;; @param C proto
+	;; ABCDEHL____
+	;; ---------------------------------
+	;; HL = BUF = &uip_buf[UIP_LLH_LEN]
+	ld	hl, #_uip_buf
+	ld	de, #UIP_LLH_LEN
+	add	hl, de
+	push	hl
+	
+	;; HL = BUF->len[0]
+	push	ix
+	ld	ix, #_OFFSET_TCPIP_HDR_LEN
+	ld	e, 0(ix)
+	ld	d, 1(ix)
+	add	hl, de
+	pop	ix
+	
+	;; DE = upper layer length
+	ld	d, (hl)
+	inc	hl
+	ld	e, (hl)
+#if UIP_CONF_IPV6
+#else
+	ld	a, e
+	sub	a, #UIP_IPH_LEN
+	ld	e, a
+	jr	nc, _upper_layer_chksum_setlen2
+	dec	d
+_upper_layer_chksum_setlen2:
+#endif
+	;; bc = upper_leyer_len + proto
+	ld	b, d
+	ld	a, e
+	add	a, c
+	ld	c, a
+	jr	nc, _upper_layer_chksum_setlen3
+	inc	b
+_upper_layer_chksum_setlen3:
+	pop	hl		; BUF
+	push	de
+	push	ix
+	ld	ix, #_OFFSET_TCPIP_HDR_SRCIPADDR
+	ld	e, 0(ix)
+	ld	d, 1(ix)
+	add	hl, de
+	ld	e, l
+	ld	d, h
+	ld	ix, #_SIZEOF_UIP_IPADDR_T
+	ld	l, 0(ix)
+	ld	h, 1(ix)
+	pop	ix
+	sla	l
+	rl	h
+	push	hl
+	push	de
+	push	bc
+	call	_uip_arch_chksum		; hl = sum
+	pop	af
+	pop	af
+	pop	af
+	;; de is still stacked
+
+	ld	b, h
+	ld	c, l
+	ld	hl, #_uip_buf
+	ld	de, #UIP_IPH_LEN	
+	add	hl, de
+_upper_layer_chksum_call:
+	ld	de, #UIP_LLH_LEN
+	add	hl, de
+	push	hl
+	push	bc
+	call	_uip_arch_chksum
+	pop	af
+	pop	af
+	pop	af
+
+	ld	a, h
+	or	a, l
+	jr	nz, _upper_layer_htons
+	ld	hl, #0xffff
+	jr	_upper_layer_ret
+_upper_layer_htons:
+	ld	a, l
+	ld	l, h
+	ld	h, a
+_upper_layer_ret:
+__endasm;
+}
+
+/*--------------------------------------------------------------------------*/
+u16_t
+uip_ipchksum(void)
+{
+__asm
+	;; ---------------------------------
+	;; u16_t uip_ipchksum(void);
+	;; Stack; retl reth
+	;; ABCDEHL____
+	;; return HL
+	;; ---------------------------------
+ 	ld	hl, #UIP_IPH_LEN
+ 	push	hl
+	;; HL = BUF = &uip_buf[UIP_LLH_LEN]
+	ld	hl, #_uip_buf
+	;; BC = sum = 0
+	ld	bc, #0
+	jp	_upper_layer_chksum_call
+__endasm;
+}
+
+/*--------------------------------------------------------------------------*/
+#if UIP_CONF_IPV6
+u16_t
+uip_icmp6chksum(void)
+{
+__asm
+	;; ---------------------------------
+	;; u16_t uip_icmp6chksum(void);
+	;; Stack; retl reth
+	;; ABCDEHL____
+	;; return HL
+	;; ---------------------------------
+	ld	c, #UIP_PROTO_ICMP6
+	jp	_upper_layer_chksum
+__endasm;
+}
+#endif /* UIP_CONF_IPV6 */
+
+/*--------------------------------------------------------------------------*/
+u16_t
+uip_tcpchksum(void)
+{
+__asm
+	;; ---------------------------------
+	;; u16_t uip_tcpchksum(void);
+	;; Stack; retl reth
+	;; ABCDEHL____
+	;; return HL
+	;; ---------------------------------
+	ld	c, #UIP_PROTO_TCP
+	jp	_upper_layer_chksum
+__endasm;
+}
+
+/*--------------------------------------------------------------------------*/
+#if UIP_UDP_CHKSUMS
+u16_t
+uip_udpchksum(void)
+{
+__asm
+	;; ---------------------------------
+	;; u16_t uip_udpchksum(void);
+	;; Stack; retl reth
+	;; ABCDEHL____
+	;; return HL
+	;; ---------------------------------
+	ld	c, #UIP_PROTO_UDP
+	jp	_upper_layer_chksum
+__endasm;
+}
+#endif /* UIP_UDP_CHKSUMS */
+/*--------------------------------------------------------------------------*/