数据链路层发送与接收的处理过程及涉及到的模块

et，当前复帧的最后一个octe除外，等于0xFC时，那么当前数据帧的最后的octet将用/F/=/K28.7/来代替。

在接收器中，在接收到对齐标志符/F/时，接收器需要用0xFC替代。

1.3.1.4 Frame alignment character generator

对齐标志符的检测与校准的处理过程如图24所示，具体的变量信息解释如表4所示，当数据流中没有提供足够的机会产生数据对齐标志符时，数据帧的对齐的校准的功能可以通过控制接口屏蔽。

图24：Frame alignmentcharacter generator

Variable

Meaning

7C_octet

Asserted when the scrambler outputs a 0x7C (28.3) octet

alignment_sent

Used to indicate a /K28.3/ or /K28.7/ has been sent in the previous frame.

FC_octet

Asserted when the scrambler outputs a 0xFC (28.7) octet

frame_end

Asserted by transmitter to indicate end of frame.

(multi)frame_start

Asserted by transmitter to indicate start of frame for devices belonging to the NMCDA-SL device class, or start of multiframe for devices belonging to other device classes. (See clause 9).

lane_seq_end

Asserted by transmitter to indicate end of initial lane alignment sequence

multiframe_end

Asserted by transmitter to indicate end of multiframe. Only to be asserted if both sides of the lane support lane synchronization.

NewOvalue

Value of last octet in current frame

OldOvalue

Used for storage of last octet in frame

SEND_A

Send /K28.3/ symbol

SEND_DATA

Send code group belonging to current data octet

SEND_F

Send /K28.7/ symbol

SEND_K

Send /K28.5/ symbol

SEND_LANE_SEQ

Send initial lane alignment sequence

sync_request_tx

asserted when transmitter detects a synchronization request

1.3.1.5 Frame alignment monitoring andcorrection

对齐标志符的检测与校准的处理过程如图25所示，具体的变量信息解释如表5所示，当数据流中没有提供足够的机会产生数据对齐标志符时，数据帧的对齐的校准的功能可以通过控制接口屏蔽。

图25：Frame alignmentmonitoring and correction

Variable

Meaning

A_received

Asserted when the current symbol, before possible substitution in lane alignment monitoring, corresponds to control character K28.3 Note: detection of K28.3 is not required in NMCDA-SL DACs.

CROSS_COUPLING

Frame misalignment expected because of cross coupling between lane and frame alignment

F

Number of octets per frame

F_received

Asserted when the current symbol corresponds to control character K28.7

Ocounter

Counter used to mark the position of the current octet in the frame. Octet indexing starts from 0.

previous_AF_position

Variable into which to store the position in the frame of a K28.3 or K28.7 symbol

REPLACE_ALIGNMENT_CHARACTER

Replace the alignment character at the decoder output by:

? The data character decoded or used at the same position in the previous frame when scrambling is disabled

? The data character with the same value when scrambling is enabled

?

Mark the possition of a K28.3 character if needed in subsequent lane synchronization or lane alignment monitoring.

RESET_OCTET_COUNTER

Reset octet counter to zero at reception of next octet

VALID

Asserted by receiver to indicate that the current symbol is a valid symbol given the current running disparity.

1.4 Initial lane synchronization

在正常数据的发送与接收前，需要对系统进行通道间的同步，以保证不同通道数据在接收输出是同步的，在一个合适的时间点上，所以的发送器将同时发送字节对齐标志位/A/=/28.3，但是由于不同通道间的延时不同，会导致接收器接收到标志字符的时间是不同的。所以当接收器接收到标志字符/A/时，每一个接收器都将从A以后的序列存储起来，并通过ready标准位通知其他通道，该通道已经接收到有效的对齐字符，当系统中