AW: [Sdcc-user] Calculating IP Checksum

[<MSoegtrop@Michael-Soegtrop.de>]

Ever thought of trying it with plain C ?

Best regards,

Michael

> -----Urspr=FCngliche Nachricht-----
> Von: sdc...@li...=20
> [mailto:sdc...@li...] Im Auftrag von=20
> Olaniyi Bajomo
> Gesendet: Donnerstag, 13. M=E4rz 2003 15:45
> An: sdc...@li...
> Betreff: [Sdcc-user] Calculating IP Checksum
>=20
>=20
> Hello guys/Gals I have a small problem. I want biuld an=20
> TCP/IP packet in my code and calculate the checksum for IP=20
> and the TCP. but for some reason I can't get my checksum=20
> program to so it. All it those is perfrom 16bit 2's=20
> complement addition of a buffer that contains the IP pseudo=20
> header, the TCP header and data. but I think there is a=20
> problem when ever the summation results in 0xff in any of my=20
> 8bit result registers as I dont think this is treated as a=20
> carry or am I wrong? I have the code  attached to=20
> this email. if anyone has a better idea as to how to do this=20
> please let me know. thanks
>=20
> ------------------------CODE STRIP-----------------------------
>=20
> code unsigned int ip_checksum(xdata u_int16_t *Ip_Pak, int=20
> pckLength) {
> 	Ip_Pak;
> 	pckLength;
> // first 16bit set to r1 r2
> // second 16bit set to r5 r6
> // pckLength set to _ip_checksum_PARM_2
>   _asm
> =09
> 	mov r3, _ip_checksum_PARM_2
> 	mov r4, (_ip_checksum_PARM_2+1)
> 	mov a ,r3    // divide lenght by 2
> 	clr c        // clear carry
> 	rrc a        // shift lower length by 1 to right
> 	mov r3,a     // save lower
> 	mov a,r4   =20
> 	clr c
> 	rrc a         // shift high length by 1 to right
> 	mov r4,a      // save higher
> 	movx a, @dptr
> 	mov r1,a      // get high byte of 16 bit numer
> 	inc dptr
> 	movx a, @dptr
> 	mov r2,a	   // get lower byte of 16bit number
> 	dec r3
>  loop:
> 	inc dptr
> 	movx a, @dptr =20
> 	mov r5, a      // get next number
> 	inc dptr
> 	movx a, @dptr
> 	add a,r2       // add lower bytes
> 	mov r2,a
> 	;clr a
> 	mov a,r1
> 	addc a,r5     // add carrys
> 	;add a,r5      // add higher byte
> 	mov r1,a      // store addition=20
> 	clr a
> 	addc a,r2     // add carry to lower byte
> 	mov r2,a
> 	djnz r3 , loop
> 	cjne r4,#0x00,high
>   finish:
>      mov a, r1
> 	 cpl a
> 	 mov dph,a
> 	 mov a, r2
> 	 cpl a
> 	 mov dpl,a
> 	 ajmp end
>   high:
>     djnz r4,loop
> 	ajmp finish
>   end:
>  _endasm;
> }
> ------------------END CODE STRIP-----------------------------
>=20
> Please HELP!!!
>=20
> Charles
> --=20
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