Vic 20 network - software by Lee Davison

If you want to talk IP over an ethernet network this is probably one of the most important protocols to implement. What it does is allow other machines to discover your hardware address automatically and talk to you. It's not absolutely necessary but without it you will need to do a lot of manual configuration.

; ********************************************************************* ; construct a reply to an ARP request aimed at us ; see RFC826 for a description of the ARP packet LAB_21000 LDA arp_buff+ARP_hrdsp_l ; hardware type - always $01 CMP #$01 ; check type BNE LAB_20350 ; exit if incorrect LDA arp_buff+ARP_prtsp_h ; hardware protocol high byte CMP #$08 ; check protocol BNE LAB_20350 ; exit if incorrect LDA arp_buff+ARP_prtsp_l ; hardware protocol low byte BNE LAB_20350 ; exit if incorrect LDA arp_buff+ARP_hrd_len ; hardware (MAC) address length CMP #$06 ; check length BNE LAB_20350 ; exit if incorrect LDA arp_buff+ARP_prt_len ; protocol (IP) address length CMP #$04 ; check length BNE LAB_20350 ; exit if incorrect LDA arp_buff+ARP_code_l ; type of packet CMP #$01 ; check type BNE LAB_20350 ; exit if incorrect LDX #arp_ofs+ARP_dst_ip ; index protocol destination address JSR match_ip ; compare with our IP address BNE LAB_20350 ; exit if not for us ; we have recognised the packet as correct and the target as us ; so set up the buffer for transmit ; do MAC addresses LDX #$05 ; set index/count LAB_21050 LDA arp_buff+ARP_src_mac,X ; copy source MAC address byte STA pk_buff+ET_dst_adr,X ; save destiantion MAC address byte STA arp_buff+ARP_dst_mac,X ; save destiantion MAC address byte LDA mac_ours,X ; get our MAC address byte STA pk_buff+ET_src_adr,X ; save source MAC address byte STA arp_buff+ARP_src_mac,X ; save source MAC address byte DEX BPL LAB_21050 ; loop if not all done ; do IP addresses LDX #$03 ; set index/count LAB_21055 LDA arp_buff+ARP_src_ip,X ; get source IP address byte STA arp_buff+ARP_dst_ip,X ; save destination IP address byte LDA ip_ours,X ; get our IP address byte STA arp_buff+ARP_src_ip,X ; save source IP address byte DEX ; increment index BPL LAB_21055 ; loop if not all done ; make it an ARP reply LDA #$02 ; set op type to reply STA arp_buff+ARP_code_l ; save op type LDA #$2A ; ARP reply length low byte STA tx_len_l ; set Tx length low byte LDA #$00 ; ARP reply length high byte STA tx_len_h ; set Tx length high byte ; packet set up, now Tx it ; *********************************************************************

Constructing the reply leads straight into transmitting the packet. With the 3Com card packets do not have to be padded out to minimum size, this is done by the card, but they do need to be a whole number of longwords (32 bits) in length. To ensure this the routine pads out any short packets with null bytes.

This is the routine that is used to transmit all the packets over the network.

; ********************************************************************* ; Tx ethernet packet, tx_len is the packet length LAB_21200 LDA tx_len_l ; get Tx length low byte STA tc_l ; save to temp count STA data_reg ; save to NIC LDA tx_len_h ; get Tx length high byte STA tc_h ; save to temp count ORA #$80 ; generates an interrupt when sent STA data_reg ; save to NIC LDY #$00 ; clear index STY data_reg ; save to NIC STY data_reg ; save to NIC ; header written, now write data LDA #>pk_buff ; get buffer pointer high byte STA tp_h ; save to temp pointer high byte LDA #<pk_buff ; get IP buffer pointer low byte STA tp_l ; save to temp pointer low byte LAB_22105 LDA (tp_l),Y ; get byte from IP buffer STA data_reg ; save to NIC INY ; increment index (pointer low byte) BNE LAB_22110 ; branch if no overflow INC tp_h ; else increment pointer high byte LAB_22110 DEC tc_l ; decrement count low byte BNE LAB_22105 ; loop if not all done DEC tc_h ; else decrement count high byte BPL LAB_22105 ; loop if not all done ; now calculate longword remainder LDA tx_len_l ; get count low byte AND #$03 ; do MOD 4 BEQ LAB_21220 ; exit if no remainder ; else pad to next longword EOR #$03 ; do 3-MOD TAX ; copy to index LDA #$00 ; clear A LAB_21215 STA data_reg ; save to NIC DEX ; decrement count BPL LAB_21215 ; loop if not all done LAB_21220 RTS ; *********************************************************************

Last page update: 29th February, 2004.

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