; -----------------------------------------------------------------------------
; interrupt
; -----------------------------------------------------------------------------
.int_received
- repeat
-- get data
- until EOF or Length > 1518 <-- ethernet type II frame
- until EOF or Length > 1526 <-- complete ethernet frame
- if length > 1518 then discard
LDA &F4
PHA
LDA #&00			\ change this
STA &F4
STA &FE30
PHX
JSR ethernet_frame_received
PLX
PLA
STA &F4
STA &FE30
PLA
RTI

; -----------------------------------------------------------------------------
; Ethernet frame received
; -----------------------------------------------------------------------------
.ethernet_frame_received
JSR calc_ethernet_crc		\ calculate frame crc
LDX #&03			\ crc size is 4 bytes

.crc_check_loop
LDA calced_crc,X		\ check if calculated crc is same as frame crc
CMP data+1514,X
BNE exit
DEX
BPL crc_check_loop
				\ check if frame is for us
LDX #&05			\ mac address is 6 bytes

.mac_check_loop
LDA my_mac_addr,X
CMP data,X
BNE check_frame_broadcast
DEX
BPL mac_check_loop
BMI frame_is_for_us		\ it's our mac address, so jump for further processing

.check_frame_broadcast		\ check if frame is broadcast
LDA data+&6
AND data+&07
AND data+&08
AND data+&09
AND data+&0A
AND data+&0B
INC A
BNE exit

.frame_is_for_us
LDA data+&0C
CMP #&08			\ check if ethertype msb is 08xx
BNE exit
LDA data+&0D
BNE frame_is_for_us1		\ is ethertype 0800 (IP)
JMP ip_received			\ yes, jump to ip packet received

.frame_is_for_us1
CMP #&06			\ is ethertype 0806 (ARP)
BNE frame_is_for_us2
JMP arp_received		\ yes, jump to arp packet received

frame_is_for_us2
CMP #&35			\is ethertype 0835 (RARP)
BNE exit
JMP rarp_received

.exit
RTS

; -----------------------------------------------------------------------------
; IP packet received
; -----------------------------------------------------------------------------
.ip_received
\\\\\offset = 0x000E
LDA data
AND #&F0			\ mask out version bits
CMP #4				\ is it version 4?
BNE exit			\ no, then exit
JSR calc_ip_crc			\ calculate packet crc
LDA calced_crc
CMP data+&000A			\ check crc lsb
BNE exit
LDA calced_crc+1
CMP data+&000B			\ check crc msb
BNE exit

				\ check for our ip address
LDX #&03			\ ip address size is 4 bytes

.ip_address_check_loop
LDA data+&000C,X		\ check if ip address is our ip address
CMP my_ip_address,X
BNE check_ip_broadcast
DEX
BPL ip_address_check_loop

				\ check for ip broadcast
LDA data+&000C,X
AND data+&000D,X
AND data+&000E,X
AND data+&000F,X
INC A
BNE exit

LDA data+&0009			\ check ip protocol number
CMP #&01			\ is it ICMP?
BEQ icmp_received		\ yes, then jump
CMP #&06			\ is it TCP?
BEQ tcp_received		\ yes, then jump
CMP #&17			\ is it UDP?
BEQ udp_received		\ yes, then jump