Data Sheet

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20
iEthernet
W5200
The timeout of W5200 can be configurable with RTR and RCR. W5200’s timeout has Address
Resolution Protocol (ARP) and TCP retransmission timeout.
At the ARP (Refer to RFC 826, http://www.ietf.org/rfc.html) retransmission timeout, W5200
automatically sends ARP-request to the peer’s IP address in order to acquire MAC address
information (used for communication of IP, UDP, or TCP). As waiting for ARP-response from the
peer, if there is no response during the time set in RTR, Timeout occurs and ARP-request is re-
transmitted. It is repeated as many as ‘RCR + 1’ times.
Even after ARP-request retransmissions are repeated ‘RCR + 1’ times, if there is no ARP-
response, the final timeout occurs and Sn_IR(TIMEOUT) becomes ‘1’.
The value of final timeout (ARP
TO
) of ARP-request is as below.
At the TCP packet retransmission timeout, W5200 transmits TCP packets (SYN, FIN, RST, DATA
packets) and waits for the acknowledgement (ACK) during the time set in RTR and RCR. If
there is no ACK from the peer, Timeout occurs and TCP packets (sent earlier) are
retransmitted. The retransmissions are repeated as many as ‘RCR + 1’ times. Even after TCP
packet retransmissions are repeated ‘RCR +1’ times, if there is no ACK from the peer, final
timeout occurs and Sn_SR is changed to ‘SOCK_CLOSED” at the same time with
Sn_IR(TIMEOUT) = ‘1’
Ex) When RTR = 2000(0x07D0), RCR = 8(0x0008),
ARP
TO
= 2000 X 0.1ms X 9 = 1800ms = 1.8s
TCP
TO
= (0x07D0 + 0x0FA0 + 0x1F40 + 0x3E80 + 0x7D00 + 0xFA00 + 0xFA00 + 0xFA00 + 0xFA00) X 0.1ms
= (2000 + 4000 + 8000 + 16000 + 32000 + ((8 - 4) X 64000)) X 0.1ms
= 318000 X 0.1ms = 31.8s
The value of final timeout (TCP
TO
) of TCP packet retransmission can be calculated as below,
PATR (Authentication Type in PPPoE mode) [R] [0x001C-0x001D] [0x0000]
This register notifies authentication method that has been agreed at the connection with
PPPoE Server. W5200 supports two types of Authentication method - PAP and CHAP.
Value Authentication Type
0xC023 PAP
0xC223 CHAP
M
TCP
TO
= ( Σ (RTR X 2
N
) + ((RCR-M) X RTR
MAX
) ) X 0.1ms
N=0
N : Retransmission count, 0 <= N <= M
M : Minimum value when RTR X 2
(M+1)
> 65535 and 0 <= M <= RCR
RTR
MAX
: RTR X 2
M
ARP
TO
= (RTR X 0.1ms ) X ( RCR + 1 )