LAN8818DSLASHKDX datasheet(44/101 Pages) MICROCHIP

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LAN8818D

DS00005832C-page 44

PCH/MCH Bytes 1 and 2 control frame preemption and timestamping. The following values are used:

• PktTyp[1:0] = 00 (other values reserved)

• SubPortID[3:0] = Device port number (0, 1, 2 or 3)

• ExtTy[1:0] = 01 (preemption disabled on this PHY port) or 10 (preemption enabled on this PHY port). ExtTy will be

the same value for all frames on a port.

• Extension[39:32] convey preemption state. Refer to the USGMII specification for details.

- Preemption Verify and Respond mPackets are passed transparently across the Q-USGMII using Extension

values. The device does not generate or respond to these mPackets, it is left to the Q-USGMII link partner to

handle Preemption Verification.

• Extension[31:0] = (three different possible formats available through configuration registers)

- [0,0,30-bit arrival nanoseconds] (0.30 format)

- [2-bit seconds, 30-bit arrival nanoseconds] (2.30 format)

- [32-bit arrival nanoseconds] (0.32 format)

• CRC[7:0] = CRC-8 covering PCH/MCH as per USGMII specification

5.9.3.2

PCH Mode TX

In PCH mode TX, departing frames arrive from the QSGMII RX functions with their preamble replaced with a PCH or

MCH RX header. 1588 frames of interest are identified by the device based on PCH or MCH header fields. Note,

QSGMII RX and 1588 TX are the same direction, MAC to PHY.

PCH/MCH Bytes 2-4 control frame preemption and timestamping. The following values are used:

• PktTyp[1:0] = ‘00’

• SubPortID[3:0] = Device port number (0, 1, 2 or 3)

• Extension[39:32] = convey preemption state. Refer to the USGMII specification for details.

- Preemption Verify and Respond mPackets are passed transparently across the Q-USGMII using Extension

values. The device does not generate or respond to these mPackets, it is left to the Q-USGMII link partner to

handle Preemption Verification.

• PCH (preemption enabled, PCH only supports two-step):

- All frames on the port are expected to have ExtTy[1:0] = ‘10’.

- However, frames with ExtTy[1:0] = ‘00’ are treated as valid unfragmented frames. These frames will be

passed to the line with valid preambles and will not be counted as Extension Type Mismatch errors.

- Frames with ExtTy[1:0] = ‘01’ or ‘11’ are treated as invalid frames. They are counted as Extension Type

Mismatch errors and discarded by the transmit PHY.

- Extension[31] = indicates a departure timestamp is to be captured for this frame

FIGURE 5-6:

PCH / MCH RX HEADER FORMAT (FROM QSGMII)

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Byte 6

Byte 7

SPD

0xfb

CRC[7:0]

Extension [15:0]

Signature

IDLE

(0x00)

Packet

Data

Extension [39:16]

Q-USGMII Rx Format: PCH / MCH Header

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Byte 6

Byte 7

SPD

0xfb

IDLE

(0x00)

Packet

Data

0x55

QSGMII Format (same Tx and Rx): standard Ethernet preamble

0x55

SFD or

SMD

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