LAN9250 datasheet(305/421 Pages) MICROCHIP

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DS00001913A-page 305

LAN9250

FORCE_ERR_DIS) field in the 1588 Port RX Timestamp Insertion Configuration Register (1588_RX-

_TS_INSERT_CONFIG).

Note:

An original UDP checksum value of 0x0000 indicates that the checksum is not included and is considered

a pass.

Note:

The original UDP checksum is calculated over the entire UDP payload as indicated by the UDP length field

and not the assumed PTP packet length.

Note:

The original UDP checksum calculation does not included layer 2 pad bytes, if any.

• For IPv6, the two bytes beyond the end of the PTP message are modified so that the original UDP checksum is

correct for the modified payload. These bytes are updated by accumulating the differences between the original

frame data and the substituted data using the mechanism defined in IETF RFC 1624.

If the original UDP checksum was invalid, a receive symbol error is forced and the 1588 Port RX Checksum

Dropped Count Register (1588_RX_CHKSUM_DROPPED_CNT) incremented.

This can be disabled by the RX PTP Bad UDP Checksum Force Error Disable (RX_PTP_BAD_UDP_CHKSUM_-

FORCE_ERR_DIS) field in the 1588 Port RX Timestamp Insertion Configuration Register (1588_RX-

_TS_INSERT_CONFIG).

Note:

Since the two bytes beyond the end of the PTP message are modified based on the differences between

the original frame data and the substituted data, an invalid incoming checksum would always result in an

outgoing checksum error.

Note:

An original UDP checksum value of 0x0000 is invalid and is considered a fail.

Note:

For IPv6, the UDP checksum calculation includes the IPv6 Pseudo header. Part of the IPv6 Pseudo header

is the final IPv6 destination address.

If the IPv6 packet does not contain a Routing header, then the final IPv6 destination address is the destina-

tion address contained in the IPv6 header.

If the IPv6 packet does contain a Routing header, then the final IPv6 destination address is the address in

the last element of the Routing header.

Note:

The original UDP checksum is calculated over the entire UDP payload as indicated by the UDP length field

and not the assumed PTP packet length.

Note:

The original UDP checksum calculation does not included layer 2 pad bytes, if any.

Note:

The two bytes beyond the end of the PTP message are located by using the messageLength field from the

PTP header.

• The frame FCS is recomputed.

If the original FCS was invalid, a bad FCS is forced.

• If the frame has a receive symbol error(s), a receive symbol error indication will be propagated at the same nibble

location(s).

Note:

FCS and UDP checksums are only updated if the frame was actually modified. If no modifications are done,

the existing FCS and checksums are left unchanged.

14.2.1.5

Ingress Message Filtering

PTP messages can be filtered upon receive. Following the determination of packet format and qualification of the packet

as a PTP message above, the PTP header is checked for ANY of the following.

• The messageType field of the PTP header is checked and those messages that have their RX PTP Message Type

Filter Enable (RX_PTP_MSG_FLTR_EN[15:0]) bits in the 1588 Port RX Filter Configuration Register (1588_RX_-

FILTER_CONFIG) set will be filtered. Typically Delay_Req and Delay_Resp messages are filtered in peer-to-peer

transparent clocks.

• The versionPTP field of the PTP header is checked against the RX PTP Version (RX_PTP_VERSION[3:0]) field in

the 1588 Port RX Timestamp Configuration Register (1588_RX_TIMESTAMP_CONFIG). If the RX PTP Version

Filter Enable (RX_PTP_VERSION_FLTR_EN) bit in the 1588 Port RX Filter Configuration Register (1588_RX_-

FILTER_CONFIG) is set, messages with a non-matching version will be filtered. A version setting of 0 allows any

PTP version and would not cause filtering.

Note:

Support for the IEEE 1588-2002 (v1) packet format is not provided.

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