LAN9250 datasheet(303/421 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS00001913A-page 303

LAN9250

Note:

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

If the FCS and checksum tests pass:

• The latency adjusted, 1588 Clock value, saved above at the start of the frame, is recorded into the 1588 Port RX

Ingress Time Seconds Register (1588_RX_INGRESS_SEC) and 1588 Port RX Ingress Time NanoSeconds Reg-

ister (1588_RX_INGRESS_NS).

• The messageType and sequenceId fields and 12-bit CRC of the portIdentity field of the PTP header are recorded

into the Message Type (MSG_TYPE), Sequence ID (SEQ_ID) and Source Port Identity CRC (SRC_PRT_CRC)

fields of the 1588 Port RX Message Header Register (1588_RX_MSG_HEADER).

The 12-bit CRC of the portIdentity field is created by using the polynomial of X12 + X11 + X3 + X2 + X + 1.

• The corresponding maskable 1588 RX Timestamp Interrupt (1588_RX_TS_INT) is set in the 1588 Interrupt Status

Up to four receive events are saved per port with the count shown in the 1588 RX Timestamp Count (1588_RX-

_TS_CNT[2:0]) field in the 1588 Port Capture Information Register (1588_CAP_INFO). Additional events are not

recorded. When the appropriate 1588 RX Timestamp Interrupt (1588_RX_TS_INT) bit is written as a one to clear, 1588

RX Timestamp Count (1588_RX_TS_CNT[2:0]) will decrement. If there are remaining events, the capture registers will

update to the next event and the interrupt will set again.

PDELAY_REQ INGRESS TIME SAVING

One-step Pdelay_Resp messages sent by the Host, require their correctionField to be calculated on-the-fly to include

the turnaround time between the ingress of the Pdelay_Req and the egress time of the Pdelay_Resp.

The 1588 Port RX Pdelay_Req Ingress Time Seconds Register (1588_RX_PDREQ_SEC) and the 1588 Port RX Pde-

lay_Req Ingress Time NanoSeconds Register (1588_RX_PDREQ_NS) hold the ingress time of the Pdelay_Req mes-

sage.

The 1588 Port RX Pdelay_Req Ingress Correction Field High Register (1588_RX_PDREQ_CF_HI) and the 1588 Port

RX Pdelay_Req Ingress Correction Field Low Register (1588_RX_PDREQ_CF_LOW) hold the correctionField of the

Pdelay_Req message.

These registers can be set by S/W prior to sending the Pdelay_Resp message.

Alternatively, these registers can be updated by the H/W when the Pdelay_Req message is received. This function is

enabled by the Auto Update (AUTO) bit in the 1588 Port RX Pdelay_Req Ingress Time NanoSeconds Register

(1588_RX_PDREQ_NS) independent from the RX PTP Message Type Enable (RX_PTP_MESSAGE_EN[15:0]) bits.

As above (including all applicable notes):

• The versionPTP and domainNumber fields and alternateMasterFlag in the flagField of the PTP header are

checked, if enabled.

Note:

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

• At the end of the frame, the frame’s FCS and the UDP checksum (for IPv4 and IPv6 formats) are verified, if

enabled.

If all tests pass, then the Pdelay_Req message information is updated.

14.2.1.4

Ingress Packet Modifications

INGRESS TIME INSERTION INTO PACKETS

As an alternate to reading the receive time stamp from registers and matching it to the correct frame received in the

Host MAC, the saved, latency adjusted, 1588 Clock value can be stored into the packet.

This function is enabled via the RX PTP Insert Timestamp Enable (RX_PTP_INSERT_TS_EN) and RX PTP Insert

Timestamp Seconds Enable (RX_PTP_INSERT_TS_SEC_EN) bits in the 1588 Port RX Timestamp Insertion Configu-

ration Register (1588_RX_TS_INSERT_CONFIG).

Note:

Inserting the ingress time into the packet is an additional, separately enabled, feature verses the Ingress

Time Recording described above. The capture registers are still updated as is the appropriate 1588 RX

Timestamp Interrupt (1588_RX_TS_INT) bit and the 1588 RX Timestamp Count (1588_RX_TS_CNT[2:0])

field.

Following the determination of packet format and qualification of the packet as a PTP message above, the PTP header

is checked for ALL of the following.

• The messageType field of the PTP header is checked and only those messages enabled via the RX PTP Mes-

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