1 - 數據鏈路層發送與接收的處理過程及涉及到的模塊

Code groupsynchronization 同步的狀態機轉換圖如圖23所示，變量的具體意義在表1中有詳細的描述。

圖23：Code groupsynchronization state machine

Variable

Meaning

Icounter

Counter used in the CS_CHECK phase to count the number of invalid symbols

INVALID

Asserted by receiver to indicate that the current symbol is an invalid symbol given the current running disparity.

K_received

Asserted when the current symbol corresponds to control character K28.5

Kcounter

Counter used in the CS_INIT phase to count the number of valid K28.5 symbols

sync_request

Asserted by receiver when loss of code group synchronization has been detected. Note that sync_request does not drive SYNC~ directly, as SYNC~ assertion/de-assertion is based on more than just the sync_request signal described here.

VALID

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

Vcounter

Counter used in the CS_CHECK phase to count the number of successive valid symbols

code groupsynchronization只需要在SYNC有效時進行，而在數據的正常傳輸時，兩個相鄰字節中的某1bit出現錯誤，也將有可能出現comma碼，而此時的comma碼將不能用來作為同步的檢測的標準。

1.1.2 Initial frame synchronization

Initial framesynchronization 的狀態機如圖24所示，該系統復位時，狀態機將進入initial state，octet counter 將會被清零，而的code group synchronization 將在系統復位后生成同步請求，在這種情況下，framesynchronization 將一直處于initialstate。

圖23：frame synchronizationstate machine

Frame synchronization的狀態機將在code group synchronization完成后，并且發送器停止發送K碼后進入FS_DATA狀態，在該狀態下，octet counter將會進行計算，以標記當前的octet在frame中的位置，octet counter的計數范圍是：0 到F-1.如果有同步請求狀態機將直接回到FS_INIT狀態，但是如果有各個接受器的情況下，其他接受器發送SYNC請求時，當前接收器并不知道有同步請求的情況下，狀態機只能通過檢測連續的K28.5來判斷狀態機是否跳轉。

如果K28.5被檢測到，狀態機將進入FS_CHECK狀態，在FS_CHECK狀態中，octet counter將繼續計數，如果有4個K28.5被檢測到，狀態機將直接跳轉到initial 狀態。

Variable

Meaning

any_sync_request

A sync request asserted by any receiver connected to the link.

CHECK_ALIGNMENT

Perf orm frame alignment monitoring, see subclause 7.3

Number of octets per frame

Kcounter

Counter used in the FS_CHECK phase to count the number of K28.5 symbols

K_received

Asserted when the current symbol corresponds to control character K28.5 (valid or invalid)