W5200 datasheet(20/88 Pages) WIZNET

20 / 88 page

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 (ARPTO) 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),

ARPTO = 2000 X 0.1ms X 9 = 1800ms = 1.8s

TCPTO = (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 (TCPTO) 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

TCPTO = (

Σ(RTR X 2N ) + ((RCR-M) X RTRMAX) ) X 0.1ms

N=0

: Retransmission count, 0 <= N <= M

: Minimum value when RTR X 2(M+1) > 65535 and 0 <= M <= RCR

RTRMAX : RTR X 2M

ARPTO

=(RTR X 0.1ms ) X ( RCR + 1 )

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