PR#3
PREFIX /A2OSX.SRC
NEW
INC 1
AUTO 6
				.LIST OFF	
*--------------------------------------
IP.IN			>PULLW ZPFrameBase1
				>PULLW ZPFrameLen1
				ldy #S.IP.PROTOCOL				
				lda (ZPFrameBase1),y
				cmp #S.IP.PROTOCOL.ICMP
				bne .2
				jmp ICMP.IN
				
.2				cmp #S.IP.PROTOCOL.UDP
				bne .3
				
				ldy #S.UDP.DSTPORT
				lda /UDP.PORT.DNS
				cmp (ZPFrameBase1),y
				bne .21
				iny
				lda #UDP.PORT.DNS
				cmp (ZPFrameBase1),y
				bne .21
				jmp DNS.IN
.21				jmp UDP.IN
				
.3				cmp #S.IP.PROTOCOL.TCP
				bne .9
				jmp TCP.IN
				
.9				sec
				rts
*--------------------------------------
* In:
*  PULLW = Start Offset
*  PULLW = End Offset
* Out:
*  Y,A = CheckSum
*--------------------------------------
IP.ComputeChecksum
				>PULLA
				clc
				adc ZPFrameBase1
				sta ZPTmpPtr1
				>PULLA
				adc ZPFrameBase1+1
				sta ZPTmpPtr1+1

				>PULLA
				clc
				adc ZPFrameBase1
				sta TmpOffset
				>PULLA
				adc ZPFrameBase1+1
				sta TmpOffset+1

				stz IP.CHECKSUM			RESET.IP.CHECKSUM	
				stz IP.CHECKSUM+1
				stz IP.CHECKSUM+2
				stz IP.CHECKSUM+3
				
				ldy #1
.1				lda (ZPTmpPtr1),y
				clc
				adc IP.CHECKSUM
				sta IP.CHECKSUM
				lda (ZPTmpPtr1)
				adc IP.CHECKSUM+1
				sta IP.CHECKSUM+1
				bcc .3
				inc IP.CHECKSUM+2
				bne .3
				inc IP.CHECKSUM+3
.3				lda ZPTmpPtr1
				clc
				adc #2
				sta ZPTmpPtr1
				bcc .4
				inc ZPTmpPtr1+1
.4				cmp TmpOffset
				bne	.1	
				lda ZPTmpPtr1+1
				cmp TmpOffset+1
				bne .1
				lda IP.CHECKSUM
				clc
				adc IP.CHECKSUM+2
				eor #$FF
				tay
				lda IP.CHECKSUM+1
				adc IP.CHECKSUM+3
				eor #$FF
				rts
*--------------------------------------
MAN
SAVE LIB/LIBTCPIP.S.IP
LOAD LIB/LIBTCPIP.S
ASM